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Article 11

Dim Forest, Bright Chimps In the rain forest of Ivory Coast, chimpanzees meet

the challenge of life by hunting cooperatively and using crude tools

Christophe Boesch and Hedwige Boesch-Achermann

Tal National Park, Ivory Coast, De- cember 3, 1985. Drumming, barking, and screaming, chimps rush through the undergrowth, little more than black shadows. Their goal is to join a group of other chimps noisily clustering around Brutus, the dominant male of this seventy-member chimpanzee com- munity. For a few moments, Brutus, proud and self-confident, stands fairly still, holding a shocked, barely moving red colobus monkey in his hand. Then he begins to move through the group, followed closely by his favorite females and most of the adult males. He seems to savor this moment of uncontested su-

periority, the culmination of a hunt high up in the canopy. But the victory is not his alone. Cooperation is essential to captUring one of these monkeys, and Brutus will break apart and share this highly prized delicacy with most of the main participants of the hunt and with the females. Recipients of large portions will, in turn, share more or less gener- ously with their offspring, relatives, and friends.

In 1979, we began a long-term study of the previously unknown chimpanzees of Tal National Park, 1,600 square miles of tropical rain forest in the Republic of the Ivory Coast (Cote d'Ivoire). Early

on, we were most interested in the chimps' use of natural hammers- branches and stones-to crack open the five species of hard-shelled nuts that are abundant here. A sea otter lying on its back, cracking an abalone shell with a rock, is a familiar picture, but no pri- mate had ever before been observed in the. wild using stones as hammers. East Africa's savanna chimps, studied for de- cades by Jane Goodall in Gombe, Tanza- nia, use twigs to extract ants and termites from their nests or honey from a bees' nest, but they have never been seen using hammerstones.

As our work progressed, we were surprised by the many ways in which the life of the Tal forest chimpanzees differs from that of their savanna coun- terparts, and as evidence accumulated, differences. in how the two populations hunt proved the most intriguing. Jane Goodall had found that chimpanzees hunt monkeys, antelope, and:wild pigs, findings confirmed by Japanese biolo- gist Toshida Nishida, who conducted a long-term study 120 miles south of Gom- be, in the Mahale Mountains.So we were not surprised to discover that the Tal chimps eat meat. What intrigued us was the degree to which they hunt coopera- tively. In 1953 Raymond Dart proposed

that group hunting and cooperation were key ingredients in the evolution of Homo sapiens. The argument has been modified considerably since Dart first put it forward, and group hunting has also been observed in some social car- nivores (lions and African wild dogs, for instance), and even some birds of prey. Nevertheless, many anthropologists still hold that hunting cooperatively and sharing food played a central role in the drama that enabled early hominids, some 1.8 million years ago, to develop the social systems that are so typically human.

We hoped that what we learned about the behavior of forest chimpan- zees would shed new light on prevailing theories of human evolution. Before we could even begin, however; we had to habituate a community of chimps to our. presence. Five long years passed before we were able to move with th'em on their daily trips through the forest, of which "our" group appeared to claim some twelve square miles. Chimpanzees are alert and shy animals, and the lim- ited field of view in the rain forest-

. about sixty-five feet at best-made finding them more difficult. We had to rely on sound, mostly their vocalizations and drumming on trees. Males often

Reprinted with permission from Natural History, September1991, pp. 50, 52-56. «J 1991 by the American Museum of Natural History. 63

2 .:. PRIMATES

drum regularly while moving through the forest: pant-hooting, they draw near a big buttress tree; then, at full speed they fly over the buttress, hitting it re- peatedly with their hands and feet. Such drumming may resound more than half a mile in the forest. In the begin- ning, our ignorance about how they moved and who was drumming led to failure more often than not, but eventu- ally we learned that the dominant males drummed during the day to let other group members know the direction of travel. On some days, however: intermit- tent drumming about dawn was the only signal for the whole day. If we were out of earshot at the time, we were often reduced to guessing.

During these difficult early days, one feature of the chimps' routine proved to be our salvation: nut cracking is a noisy business. So noisy, in fact, that in the early days of French colonial rule, one officer apparently even proposed the theory that some unknown tribe was forging iron in the impenetrable and dangerous jungle.

Guided by the sounds made by the chimps as they cracked open nuts, which they often did for hours at a time, we were gradually able to get within sixty feet of the animals. We still seldom saw the chimps themselves (they fled if we came too close), but even so, the evi- dence left after a session of nut cracking taught us a great deal about what types of nuts they were eating, what sorts of hammer and anvil tools they were using, and-thanks to the very distinctive noise a nut makes when it finally splits open-how many hits were needed to crack a nut and how many nuts could be opened per minute.

After some months, we began catch- ing glimpses of the chimpanzees before they fled, and after a little more time, we were able to draw close enough to watch them at work. The chimps gather nuts from the ground. Some nuts are tougher to crack than others. Nuts of the Panda oleosa tree are the most demand- ing, harder than any of the foods pro- cessed by present-day hunter-gatherers and breaking open only when a force of 3,500 pounds is applied. The stone ham- mers U!?edby the Tal chimps range from stones of ten ounces to granite blocks

of four to forty-five pounds. Stones of any size, however, are a rarity in the for- est and are seldom. conveniently placed near a nut-bearing tree. By observing closely, and in some cases imitating the way the chimps handle hammerstones, we learned that they have an impressive ability to find just the right tool for the job at hand. Tal chimps could remember the positions of many of the stones scat- tered, often out of sight, around a panda tree. Without having to run around re- checking the stones, they would select one of appropriate size that was closest to the tree. These mental abilities in spa- tial representation compare with some of those of nine-year-old humans.

To extract the four kernels from in- side a panda nut, a chimp must use a hammer with extreme precision. Time and time again, we have been impressed to see a chimpanzee raise a twenty- pound stone above its head, strike a nut with ten or more powerful blows, and then, using the same hammer, switch to delicate little taps from a height of only four inches. To finish the job, the chimps often break off a small piece of twig and use it to extract the last tiny fragments of kernel from the shell. In- triguingly, females crack panda nuts more often than males, a gender differ- ence in tool use that seems to be more pronounced in the forest chimps than in their savanna counterparts.

After five years of fieldwork, we were finally able to follow the chimpan- zees at close range, and gradually, we gained insights into their way of hunt- ing. One morning, for example, we fol- lowed a group of six male chimps on a three-hour patrol that had taken them into foreign territory to the north. (Our study group is one of five chimpanzee groups more or less evenly distributed in the Tal forest.) As always during these approximately monthly incursions, which seem to be for the purpose of ter- ritorial defense, the chimps were totally silent, clearly on edge and on the lookout for trouble. Once the patrol was over, however, and they were back within their own borders, the chimps Shiftedtheir at- tention to hunting. They were after mon- keys, the most abundant mammals in the forest. Traveling in large, multi-species groups, some of the forest's ten species

of monkeys are more apt than others to wind up as a meal for the chimps. The relatively sluggish and 1arge (almost thirty pounds) red colobus monkeys are the chimps' usual fare. (Antelope also live in the forest, but in our ten years at Tal, we have never seen a chimp'catch, or even pursue, one. In contrast, Gombe chimps at times do come across fawns, and when they do, they seize the oppor- tunity-and the fawn.)

The six males moved on silently, peering up into the vegetation and stop- ping from time to time to listen for the sound of monkeys. None fed or groomed; all focused on the hunt. We followed one old male, Falstaff, closely, for he tolerates us completely and is one of the keenest and most experienced hunters. Even from the rear, Falstaff set the pace; whenever he stopped, the others paused to wait for him. After thirty minutes, we heard the unmistak- able noises of monkeys jumping from branch to branch. Silently,. the chimps turned in the direction of the sounds, scanning the canopy. Just then, a diana monkey spotted them and gave an alarm call. Dianas are very alert and fast; they are also about half the weight of colobus monkeys. The chimps quickly gave up and continued their search for easier, meatier prey.

Shortly after, we heard the charac- teristic cough of a red colobus monkey. Suddenly Rousseau and Macho, two twenty-year-olds, burst into action, run- ning toward the cough. Falstaff seemed surprised by their precipitousness, but after a moment's hesitation, he also ran. Now the hunting barks of the chimps mixed with the sharp alarm calls of the monkeys. Hurrying behind Falstaff, we saw him climb up a conveniently situ- ated tree. His position, combined with those of Schubert and Ulysse, two ma- ture chimps in their prime, effectively blocked off three of the monkeys' pos- sible escape routes. But in,another tree, nowhere near any escape route and thus useless, waited the last of the hunters, Kendo, eighteen years old and the least experienced of the group. The monkeys, taking advantage of Falstaff's delay and Kendo's error, escaped.

The six males moved on and within five minutes picked up the sounds of an-

other group of red colobus. This time, the chimps approached cautiously, no- body hurrying. They screened the can- opy intently to locate the monkeys, which were still unaware of the ap- proaching danger. Macho and Schubert chose two adjacent trees, both full of monkeys, and started climbing very qui- etly, taking care not to move any branches. Meanwhile, the other four chimps blocked off anticipated escape routes. When Schubert was halfway up, the monkeys finally detected the two chimps. As we watched the: colobus monkeys take off in literal panic, the ap- propriateness of the chimpanzees' sci- entific name-Pan came to mind: with a certain stretch of the imagination, the fleeing monkeys could be shep- herds and shepherdesses frightened at the sudden appearance of Pan, the wild Greek god of the woods, shepherds, and their flocks.

Taking off in the expected direction, the monkeys were trailed by Macho and Schubert. The chimps let go with loud hunting barks. Trying to escape, two colobus monkeys jumped into smaller trees lower in the canopy. With this, Rousseau and Kendo, who had been watching from the ground, sped up into the trees and tried to grab them. Only a third of the weight of the chimps, how- ever, the monkeys managed to make it to the next tree along branches too small for their pursuers. But Falstaff had an- ticipated this move and was waiting for them. In the following confusion, Fal- staff seized a juvenile and killed it with a bite to the neck. As the chimps met in a rush on the ground, Falstaff began to eat, sharing with Schubert and Rous- seau. A juvenile colobus does not pro- vide much meat, however, and this time, not all the chimps got a share. Frustrated individuals soon started off on another hunt, and relative calm returned fairly quickly: this sort of hunt, by a small band of chimps acting on their own at the edge of their territory, does not gen- erate the kind of high excitement that prevails when more members of the community are involved.

So far we have observed some 200 monkey hunts and have concluded that success requires a minimum of three motivated hunters acting cooperatively.

Alone or in pairs, chimps succeed less than 15 percent of the time, but when

. three or four act as a group, more than half the hunts result in a kill. The chimps. seem well aware of the odds; 92 percent of all the hunts we observed were group affairs.

Gombe chimps also hunt red colobus monkeys, but the percentage of group hunts is much lower: only 36 percent. In addition, we learned from Jane Goo- dall that even when Gombe chimps' do hunt in groups, their strategies are dif- ferent. When Tal chimps anive under-a group of monkeys, the hunters scatter, often silently, usually out of sight of one another but each aware of the others' po- sitions. As the hunt progresses, they gradually close in, encircling the quarry. Such movements require that each chimp coordinate his movements with those of the other hunters, as well .as with those of the prey, at all times.

Coordinated hunts account for 63 percent of all those observed at Tal but only 7 percent of those at Gombe. Jane Goodall says. that in a Gombe group hunt, the chimpanzees typically travel together until they anive at a tree with monkeys. Then, as the chimps begin climbing nearby trees, they scatter as each pursues a different target. Goodall gained the impression that Gombe chimps boost their success by hunting independently but simultaneously,thereby disorganizingtheir prey; our impressionis that the Tal chimps owe their success to being organizedthemselves.

Just why the Gombe and Tal chimps have developed such different hunting strategies is difficult to explain, and we plan to spend some time at Gombe in the hope of finding out. In the mean- time, the mere existence of differences is interesting enough and may perhaps force changes in our understanding of human evolution. Most currently ac- cepted theories propose that some three million years ago, a dramatic climate change in Africa east of the Rift Valley turned dense forest into open, drier habi- tat. Adapting to the difficulties of life under these new conditions, our ances- tors supposedly evolved into cooperative hunters and began sharing food they caught. Supporters of this idea point out that plant and animal remains indicative

11. Dim Forest, Bright Chimps

of dry, open environments have been found at all early hominid excavation sites in Tanzania, Kenya, South Africa, and Ethiopia. That the large majority of apes in Africa today live west of the Rift - Valley appears to many' anthropologists to lend further support to the idea that a change in environment caused the common ancestor of apes and humans to evolve along a different line from those remaining in the forest.

Our observations, however, suggest quite another line of thought. Life in dense, dim forest may require more so- phisticated behavior than is commonly assumed: compared with their savanna relatives, Tal chimps show greater com- plexity in both hunting and tool use. Tal chimps use tools in nineteen different ways and have six different ways of making them, compared with sixteen uses and three methods of manufacture at Gombe.

Anthropologist colleagues of mine have told me that the discovery that some chimpanzees are accomplished us- ers of hammerstones forces them to look with a fresh eye at stone tools turned up at excavation sites. The important role played by female Tal chimps in tool use also raises the possibility that in the course of human evolution, - women may have been decisive in the development of many of the sophisticated manipulat- ive skills characteristic of our species. Tal mothers also appear to pass on their skills by actively teaching their off- spring. We have observed mothers pro- viding their young with hammers and then stepping in to help when the inex- perienced youngsters encounter diffi- culty. This help may include carefully showing how to position the nut or hold the hammer properly. Such behavior has never been observed at Gombe.

Similarly, food sharing, for a long time said to be unique to humans, seems more general in forest than in savanna chimpanzees. Tal chimp mothers share with their young up to 60 percent of the nuts they open, at least until the latter become sufficiently adept, generally at about six years old. They also share other foods acquired with tools, includ- ing honey, ants, and bone marrow. Gombe mothers share such foods much less often, even with their infants. Tal

2 .:. PRIMATES

chimps also share meat more frequently than do their Gombe relatives, some- times dividing a chunk up and giving portions away, sometimes simply allow- ing. beggars to grab pieces.

Any comparison between chimpan- zees and our hominid ancestors can only be suggestive,not definitive.But our stud- ies lead us to believe that the process of hominization may have begun inde- pendently of the drying of the environ- ment. Savanna life could even have delayed the process; many anthropologists have been struck by how slowly homi- nid-associated remains, such as the hand ax, changed after their first appearance in the Olduvai age.

Will we have the time to discover more about the hunting strategiesor other, perhaps as yet undiscovered abilities of

these forest chimpanzees? Africa's tropical rain forests, and their inhabi- tants, are threatened with extinction by extensive logging, largely to provide the Western world with tropical timber and such products as coffee, cocoa, and rnb- ber. Ivory Coast has lost 90 percent of its original forest, and less than 5 per- cent of the remainder can be considered pristine. The climate has changed dra- matically. The harmattan, a cold, dry wind from the Sahara previously un- known in the forest, has now swept through the Tal forest every year since 1986. Rainfall has diminished; all the rivulets in our study region are now dry for several months of the year.

In addition, the chimpanzee, biologi- cally very close to humans, is in demand for research on AIDS and hepatitis vac-

cines. Captive-bred chimps are avail- able, but they cost about twenty times more than wild-caught animals. Chimps taken from the wild for these purposes are generally young, their mothers hav- ing been shot during capture. For every chimp arriving at its sad destination, nine others may well have died in the forest or on the way.>Such priorities- cheap coffee and cocoa and chimpan- zees~o not do the economies of Third World countries any good in the long run, and they bring suffering and death to innocent victims in the forest. Our hope is that Brotus, Falstaff, and their families will survive, and that we and others will have the opportunity to learn about them well into the future. But there is no denying that modem times work against them and us.

__MACOSX/._Dim Forest, Bright Chimps (1).pdf

Gibbons 2011_A New View (1).pdf

28 JANUARY 2011 VOL 331 SCIENCE www.sciencemag.org 392

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New genomic data are settling an old

argument about how our species evolved

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FOR 27 YEARS, CHRIS STRINGER AND

Milford Wolpoff have been at odds about

where and how our species was born.

Stringer, a paleoanthropologist at the Nat-

ural History Museum in London, held that

modern humans came out of Africa, spread

around the world, and replaced, rather than

mated with, the archaic humans they met.

But Wolpoff, of the University of Michigan,

Ann Arbor, argued that a single, worldwide

species of human, including archaic forms

outside of Africa, met, mingled and had

offspring, and so produced Homo sapiens.

The battle has been long and

bitter: When reviewing a man-

uscript in the 1980s, Wolpoff

scribbled “Stringer’s desper-

ate argument” under a chart;

in a 1996 book, Stringer wrote

that “attention to inconvenient

details has never been part of

the Wolpoff style.” At one tense

meeting, the pair presented

opposing views in rival sessions

on the same day—and Wolpoff

didn’t invite Stringer to the

meeting’s press conference. “It

was diff icult for a long time,”

recalls Stringer.

Then, in the past year, geneticists an-

nounced the nearly complete nuclear

genomes of two different archaic humans:

Neandertals, and their enigmatic eastern

cousins from southern Siberia. These data

provide a much higher resolution view of

our past, much as a new telescope allows

astronomers to see farther back in time

in the universe. When compared with the

genomes of living people, the ancient

genomes allow anthropologists to thor-

oughly test the competing models of human

origins for the fi rst time.

The DNA data suggest not one but

at least two instances of interbreeding

between archaic and modern humans, rais-

ing the question of whether H. sapiens at that

point was a distinct species (see sidebar,

p. 394). And so they appear to refute the com-

plete replacement aspect of the Out of Africa

model. “[Modern humans] are certainly com-

ing out of Africa, but we’re fi nding evidence

of low levels of admixture wherever you

look,” says evolutionary geneticist Michael

Hammer of the University of Arizona in Tuc-

son. Stringer admits: “The story has undoubt-

edly got a whole lot more complicated.”

But the genomic data don’t prove the

classic multiregionalism model correct

either. They suggest only a small amount

of interbreeding, presumably at the margins

where invading moderns met archaic groups

that were the worldwide descendants of

H. erectus, the human ancestor that left

Africa 1.8 million years ago. “I have lately

taken to talking about the best model as

replacement with hybridization, … [or]

‘leaky replacement,’ ” says paleogeneticist

Svante Pääbo of the Max Planck Institute for

Evolutionary Anthropology in Leipzig, lead

author of the two nuclear genome studies.

The new picture most resembles so-called

A New View Of the Birth of Homo sapiens

A New View Of the Birth of Homo sapiens New genomic data are settling an old

argument about how our species evolved

NEWSFOCUS

Going back in time. A researcher extracts DNA from a fossil.

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assimilation models, which got relatively

little attention over the years. “This means

so much,” says Fred Smith of Illinois State

University in Normal, who proposed such a

model. “I just thought ‘Hallelujah! No mat-

ter what anybody else says, I was as close to

correct as anybody.’ ”

Evolving models Stringer and others fi rst proposed Africa as

the birthplace of modern humans back in the

mid-1980s. The same year, researchers pub-

lished a landmark study that traced the mater-

nally inherited mitochondrial DNA (mtDNA)

of all living people to a female

ancestor that lived in Africa about

200,000 years ago, dubbed mito-

chondrial Eve. She caught the

attention of the popular press,

landing on the cover of Newsweek

and Time.

Additional studies of living

people—from Y chromosomes to

snippets of nuclear DNA to the

entire mtDNA genome—consis-

tently found that Africans were

the most diverse genetically. This

suggests that modern humans

arose in Africa, where they had

more time to accumulate muta-

tions than on other continents

(Science, 17 November 2006,

p. 1068). Meanwhile, ancient

DNA technology also took off.

Pääbo’s group sequenced f irst

a few bits of Neandertal mito-

chondrial DNA in 1997, then

the entire mitochondrial genomes of several

Neandertals—and found them to be dis-

tinct from those of living people. So ancient

DNA, too, argued against the idea of mixing

between Neandertals and moderns. Over the

years the replacement model became the lead-

ing theory, with only a stubborn few, includ-

ing Wolpoff, holding to multiregionalism.

Yet there were a few dissenting notes. A few

studies of individual genes found evidence of

migration from Asia into Africa, rather than

vice versa. Population geneticists warned that

complete replacement was unlikely, given

the distribution of alleles in living humans.

And a few paleoanthropologists proposed

middle-of-the-road models. Smith, a former

student of Wolpoff ’s, suggested that most of

our ancestors arose in Africa but interbred with

local populations as they spread out around

the globe, with archaic people contributing to

about 10% of living people’s genomes. At the

University of Hamburg in Germany, Gunter

Brauer similarly proposed replacement with

hybridization, but with a trivial amount of

interbreeding. But neither model got much

traction; they were either ignored or lumped

in with multiregionalism. “Assimilation got

kicked so much,” recalls Smith.

Over time, the two more extreme mod-

els moved toward the middle, with most

multiregionalists recognizing that the chief

ancestors of modern humans arose in Africa.

“The broad line of evolution is pretty clear:

Our ancestors came out of Africa,” says

biological anthropologist John Relethford

of the State University of New York College

at Oneonta. “But what happens next is kind

of complex.”

Genes from the past Then in May 2010 came the Neandertals’

complete nuclear genome, sequenced from

the bones of three female Neandertals who

lived in Croatia more than 38,000 years ago.

Pääbo’s international team found that a small

amount—1% to 4%—of the nuclear DNA

of Europeans and Asians, but not of Afri-

cans, can be traced to Neandertals. The most

likely model to explain this, Pääbo says, was

that early modern humans arose in Africa

but interbred with Neandertals in the Mid-

dle East or Arabia before spreading into Asia

and Europe, about 50,000 to 80,000 years ago

(Science, 7 May 2010, pp. 680, 710).

Seven months later, on 23 Decem-

ber, the team published in Nature the com-

plete nuclear genome of a girl’s pinky fi n-

ger from Denisova Cave in the Altai Moun-

tains of southern Siberia. To their surprise,

the genome was neither a Neandertal’s nor

a modern human’s, yet the girl was alive at

the same time, dating to at least 30,000 years

ago and probably older than 50,000 years.

Her DNA was most like a Neandertal’s, but

her people were a distinct group that had long

been separated from Neandertals.

By comparing parts of the Denisovan

genome directly with the same segments of

DNA in 53 populations of living people, the

team found that the Denisovans shared 4%

to 6% of their DNA with Melanesians from

Papua New Guinea and the Bougainville

Islands. Those segments were not found in

Neandertals or other living humans.

The most likely scenario for how all this

happened is that after Neandertal and Deniso-

van populations split about 200,000 years ago,

modern humans interbred with Neandertals as

they left Africa in the past 100,000 years. Thus

Neandertals left their mark in the genomes of

living Asians and Europeans, says co-author

Montgomery Slatkin, a population geneti-

cist at the University of California, Berkeley.

Later, a subset of this group of moderns—

who carried some Neandertal DNA—headed

east toward Melanesia and interbred with the

Denisovans in Asia on the way. As a result,

Melanesians inherited DNA from both Nean-

dertals and Denisovans, with as much as 8% of

their DNA coming from archaic people, says

co-author David Reich, a population geneti-

cist at Harvard Medical School in Boston.

This means H. sapiens mixed it up with

at least two different archaic peoples, in at

least two distinct times and places. To some,

that’s starting to sound a lot like multiregion-

alism. “It’s hard to explain how good I feel

Changing views. Two models of modern human origins (left) are being challenged by new insights based on ancient DNA (right), which suggest some limited interbreeding between modern and archaic populations.

Ancient abode. A fi nger and molar (inset) of a new type of human were found in Denisova Cave, Siberia.

Years ago

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Spread of Homo erectus throughout the world

African origin for Homo erectus

50,000

100,000

X X X

Homo erectus

1,800,000

Modern humans

Multiregional Continuity

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Time in years

about 100,000

about 500,000

Inter- breeding

A fr

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Spread of Homo erectus throughout the world

African origin for Homo erectus

Out of Africa Leaky Replacement

Modern Human Lineage

Neandertal Lineage

Scenarios of Modern Human Origins

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about this,” says Wolpoff, who says that see-

ing complete replacement falsifi ed twice in

1 year was beyond his wildest expectations.

“It was a good year.”

And yet the interbreeding with archaic

humans seems limited—from 1% to 8% of

some living people’s genomes. Stringer and

many others don’t consider it full-scale multi-

regional continuity. “I think interbreeding

was at a low level,” says Slatkin, who says

that if there had been a great deal of admix-

ture, the genetic data would have revealed it

already. Low levels of interbreeding suggest

that either archaic people mated with moderns

only rarely—or their hybrid offspring had low

fi tness and so produced few viable offspring,

says population geneticist Laurent Excoffi er

of the University of Bern in Switzerland.

In any case, Reich notes that at least 90%

of our genomes are inherited from Afri-

can ancestors who

replaced the archaic

people on other con-

tinents but hybrid-

ized with them around

the margins. And that

scenario most closely

backs the assimilation

models proposed by

Smith and Brauer.

Of course, it’s possi-

ble that future data will

overturn today’s “leaky replacement” model.

Slatkin says he cannot rule out an alterna-

tive explanation for the data: The “archaic”

DNA thought to have come from mating with

Neandertals could instead stem from a very

ancient ancestor that we shared with Nean-

dertals. Most modern humans retained those

archaic sequences, but Africans lost them. But

Slatkin says this “doesn’t seem very plausi-

ble,” because it requires modern human popu-

lations with the archaic DNA and those with-

out it to have been partially isolated from each

other in Africa for hundreds of thousands of

years. And it seems even less probable that

Melanesians and Denisovans are the only

groups that retained a second set of archaic

DNA motifs from a common ancestor shared

by all modern humans, Neandertals and Den-

isovans. If those explanations do prove true,

replacement would not be falsifi ed.

In the wake of the big genome studies,

other researchers such as Hammer are scru-

tinizing DNA from more living humans

to further test the model. Researchers are

also trying to pinpoint when admixture

happened, which has signif icant conse-

quences. At just what point did we evolve

from archaic humans to become “modern”

humans? “There are still archaic [genetic]

features floating around until amazingly

recently, until 40,000 years ago,” says Ham-

mer. He wonders whether the process of

becoming modern took longer and was more

complex than once thought. “There’s no line

you can draw and say everything after this

is modern. That’s the elephant in the room.”

Meanwhile, paleoanthropologists are

searching for fossils in Asia that might belong

to the enigmatic Denisovan population—and

might yield more ancient DNA. Paleoanthro-

pologist Russell Ciochon of the University of

Iowa in Iowa City and Wolpoff say there are

several known, ambiguous fossils in Asia that

might be candidates for early Denisovans. “I

believe things were going on in Asia that we

just don’t know about,” says Ciochon. “Before

this paper on the Denisovans, we didn’t have

any insight into this. Now, with this nuclear

genome, I fi nd myself talking about ‘the Den-

isovans.’ It’s already had an impact.”

As for Stringer and Wolpoff, both now

in their 60s, their battle has mellowed. Their

views, while still distinct, have converged

somewhat, and they shared a beer at a Nean-

dertal meeting last year. “The reason we get

on well now,” says Stringer, “is we both think

we’ve been proved right.” –ANN GIBBONS

The Species Problem

Our ancestors had sex with at least two kinds of archaic humans at two different times and places— and those liaisons produced surviving children, according to the latest ancient DNA research (see main text, p. 392). But were the participants in these prehistoric encounters members of separate species? Doesn’t a species, by defi nition, breed only with others of that species?

These are the questions paleogeneticist Svante Pääbo dodged twice last year. His team pub- lished two papers proposing that both Neandertals and mysterious humans from Denisova Cave in Siberia interbred with ancient modern humans. But the researchers avoided the thorny ques- tion of species designation and simply referred to Neandertals, Denisovans, and modern humans as “populations.” “I think discussion of what is a species and what is a subspecies is a sterile aca- demic endeavor,” says Pääbo, who works at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

The question of how to defi ne a species has divided researchers for centuries. Darwin’s words in On the Origin of Species still hold: “No one defi nition has satisfi ed all naturalists.” However, many scientists use the biological species concept proposed by Ernst Mayr: “groups of actually or poten- tially interbreeding natural populations, which are reproductively isolated from other such groups.”

The draft versions of the Neandertal and Denisovan nuclear genomes show low levels of inter- breeding between each of them and modern humans. Apply Mayr’s defi nition strictly, and all three must be considered Homo sapiens. “They mated with each other. We’ll call them the same species,” says molecular anthropologist John Hawks of the University of Wisconsin, Madison.

But that’s a minority view among paleoanthropologists. Many consider Neandertals a species separate from modern humans because the anatomical and developmental differences are “an order of magnitude higher than anything we can observe between extant human populations,” says Jean-Jacques Hublin, a co-author of Pääbo’s at Max Planck. In the real world, he says, Mayr’s concept doesn’t hold up: “There are about 330 closely related species of mammals that interbreed, and at least a third of them can produce fertile hybrids.”

There’s also no agreed-upon yardstick for how much morphologic or genetic difference sepa- rates species. That’s why Pääbo’s team avoided the species question a second time with respect to the Denisovans. These hominins are known only from a scrap of bone, a single tooth, and their DNA. They are genetically closest to Neandertals. The genetic distance between Denisovans and Neandertals, in fact, is only 9% larger than that between a living Frenchman and a living San Bush- man in Africa, both of whom belong to H. sapiens. But so far Neandertals seem to have low genetic diversity, based on the DNA of six Neandertals from Russia to Spain. To Pääbo’s team, that makes the difference from the Denisovans signifi cant.

Also, the Denisovan tooth doesn’t look much like that of a Neandertal. So the team considers them a distinct population but declined to name a new species. “Why take a stand on it when it will only lead to discussions and no one will have the fi nal word?” asks Pääbo. –A.G.

E U R A S I A

A F R I C A

A U S T R A L I A

O C E A N I A

Neandertal Range

Melanesians

Denisovans

Contact zones. Modern humans from Africa interbred with Neandertals (pink). Then one group mixed with Denisovans (green) on the way to Melanesia.

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__MACOSX/._Gibbons 2011_A New View (1).pdf

Jablonski and Chaplin Skin Deep (1).pdf

__MACOSX/._Jablonski and Chaplin Skin Deep (1).pdf

Moore The Puzzling Origins of AIDS (2).pdf

with permission only. Contact [email protected].

Shortly after the 1983 discovery of the human immunodeficiency vi- rus (HIV), the pathogen responsible for AIDS, investigators became aware of a strangely similar immune deficiency disease afflicting Asian monkeys (ma- caques) held in captivity in various U.S. research labs. Soon, virologists identified the culprit: a simian immunodeficiency virus (SIV) that is found naturally in a West African monkey species, the sooty mangabey (Cercocebus atys), but is harm- less to that host. This virus, denoted SIVsm, is genetically similar to a weakly contagious form of the AIDS virus that is largely restricted to parts of West Africa, HIV-2, and thus is considered its likely precursor. More recent work has shown that the closest relative of the primary hu- man immunodeficiency virus (HIV-1) is another simian immunodeficiency virus, one carried by chimpanzees (SIVcpz).

After comparing the SIVs in chimpan- zees and sooty mangabeys with HIV-1 and HIV-2 strains, investigators conclud- ed that there must have been multiple transmission “events” from simians to humans—at least seven for HIV-2 (some of which are known from only a single person who lives near mangabeys carry- ing a uniquely similar SIV) and three for HIV-1, the virus now infecting some 40 million people worldwide.

How did SIVcpz and SIVsm cross over into humans and become patho- genic? Given the lack of historical refer- ences to AIDS-like disease in Africa pri-

or to the mid-20th century, as well as its absence previously in the New World (which imported some 10 million Afri- can slaves during the 16th through 19th centuries), that transfer appears to have happened relatively recently—exactly when is a point of considerable debate. And why did two distinct simian vi- ruses with which humans have appar- ently coexisted for centuries, or even millennia, suddenly pass into humans multiple times within a few decades?

The answers to these questions have been slow in coming, despite the con- siderable efforts of molecular biologists to understand the nature and evolution of primate immunodeficiency viruses. I am not one of those molecular biolo- gists; rather, I became a player in the field of AIDS-origin research through my interest in chimpanzee socioecol- ogy. Although I am partial to a theo- ry I helped to fashion for why AIDS emerged when it did, with time it might become clear that a competing idea bet- ter accounts for genesis of the epidemic. Or perhaps the answer will prove to lie with some complex combination of fac- tors that no single explanation presently encompasses. Whatever the case, the solution almost certainly will come from one or more of four competing theories.

Theory 1: Tainted Polio Vaccine The first theory is the most controversial. In a 1992 article in the magazine Rolling Stone, journalist Tom Curtis suggested that HIV could have resulted from the use in Africa of an experimental oral po- lio vaccine (OPV), one contaminated by a then-unknown SIV carried most prob- ably (Curtis supposed) by African green monkeys. Green-monkey kidney cells were widely used as a substrate to grow viruses for research and vaccine produc- tion. And one of the first major trials of

an experimental oral polio virus vaccine took place from 1957 to 1960 in what are now the Democratic Republic of the Con- go, Burundi and Rwanda, seemingly the “hearth” of the global AIDS epidemic. When interviewed by Curtis, Hilary Ko- prowski, the polio-vaccine pioneer who mounted that massive campaign, could not recall or find documentary evidence as to whether his group had used kid- ney cells from green monkeys or Asian macaques (which do not naturally carry an SIV). If culture media contained SIV (a possibility, given that the techniques available during that era were unable

The Puzzling Origins of AIDS

Although no one explanation has been universally accepted, four rival theories provide some important lessons

Jim Moore

Figure 1. Investigators puzzle over why the AIDS epidemic struck when it did. A simian virus very similar to HIV-1 (the HIV type re- sponsible for the vast majority of AIDS cases) is found in the chimpanzees of Central Africa, suggesting that these animals naturally harbor the progenitor virus. The leading idea is that this virus first passed through cuts to someone hunting or butchering a chimpanzee, but this theory alone cannot explain why the AIDS epidemic did not arise before the 20th century, because hunting chimpanzees for meat has presumably been going on for thousands of years. The author and two of his students sug- gested that the forced labor and population movements imposed on the natives of Central Africa during the colonial era—and the unster- ilized needles used in health campaigns as- sociated with those disruptions—might have created conditions favoring the transfer of the progenitor virus from chimpanzees to humans and its adaptation to become HIV. Vintage postcards show some relevant scenes from the region during the early part of the 20th century. Clockwise from top: vaccination in the Congo Free State (now Democratic Republic of the Congo); Haute-Sangha (a province of what is now Central African Republic), doctor vacci- nates natives in the field; French Congo (now Republic of the Congo), missionaries vaccinate in the field in the vicinity of Brazzaville; Bel- gian Congo (now Democratic Republic of the Congo), construction of a bridge over a ravine.

Jim Moore received his doctorate in biological an- thropology from Harvard in 1985, where he studied demography and sociality in primates. Since then he has been on the faculty of the University of Cali- fornia, San Diego, where his research focuses on primate behavioral ecology. Address: Anthropology Department, University of California, San Diego, La Jolla, CA 92093. Internet: [email protected]

with permission only. Contact [email protected].

to guard against unknown viruses that did not cause overt symptoms in their monkey hosts), more than 900,000 peo- ple might have received it with their medicine, laying the basis for the current epidemic.

Curtis credited this theory to Blaine Elswood, a Californian AIDS activist. Interestingly, the idea that the admin- istration of a contaminated oral polio vaccine might have been involved in the genesis of AIDS was suggested independently by two others at about the same time. The first to do so was Louis Pascal, who like Elswood is not a scientist. After years of rejections, Pascal, a New Yorker, finally man- aged in 1991 to get the University of Wollongong in Australia to publish a paper describing his ideas. Not sur- prisingly, few noticed it. Attorney Walter Kyle also published a broadly similar theory in The Lancet, a British medical journal, in 1992. Since then, writer Edward Hooper, author of the controversial 1999 book The River, has become the contaminated-vaccine the- ory’s most ardent supporter. Hooper, noting a passing mention by Curtis of a chimpanzee colony run by Koprow- ski’s team, suggested that kidneys from these chimpanzees—not from green monkeys—may have been the original source of the virus.

Multiple localized strains of HIV have now been discovered, and mass vac- cination appears unlikely to account for all of them. But the early distribution of the major pandemic strain, HIV-1 group M (for “main”), seems to fit reasonably well with the location of Koprowski’s campaigns, and the OPV theory now is applied primarily to this strain.

Contamination of OPV is the only one of the four current theories that is read- ily falsifiable: Finding the HIV-1 group M virus in a tissue sample that predated the suspect vaccine would eliminate this possibility. So far that has not happened. Still, many investigators give the theory little weight for other reasons, which has led to the widespread belief that the theory has been definitively disproved. In 2001, for example, Science magazine published a piece titled “Disputed AIDS Theory Dies its Final Death,” and Na- ture ran one under the heading “Polio Vaccines Exonerated.” Earlier this year Nature also published “Origin of AIDS: Contaminated Polio Vaccine Theory Re- futed”—a surprising title given that this theory ostensibly died three years ago.

The recent findings of various mo- lecular biologists have indeed failed to provide support for the OPV theory. For example, in 2000 a few existing samples of the vaccine from Koprowski’s home institution (the Wistar Institute in Phila-

delphia) were tested and found nega- tive for both chimpanzee DNA and SIV. However, this result did not rule out the possibility, previously suggested by Hooper, that local amplification of the live-virus vaccine in Africa (to create more doses) could have introduced the SIV. The key issue is thus whether chim- panzee kidneys were used as a culture medium at any stage of Koprowski’s vaccine program. There is eyewitness testimony on both sides of this question, and failure to find SIVcpz in a handful of samples of the live vaccine strain of the type used in Africa does not prove the virus was absent in (putative) locally produced batches.

A second reason to question the OPV theory also came to light in 2000, with a report in Science by Bette T. Korber (of Los Alamos National Laboratory) and colleagues. They used molecular differ- ences among HIV-1 group M subtypes to estimate the date of their last com- mon ancestor. The conclusion: 1931 (with 95 percent confidence limits giv- ing the range 1915 to 1941), preceding OPV administration by decades. How- ever, the calculation of such common- ancestor dates can be thrown off by ge- netic recombination among subtypes (“viral sex”), which can make such dates come out too early, and there is increas- ing evidence that such recombination may be common with HIV. So maybe this date is not right. On the other hand, independent analyses using different methods have supported the date, and an analogous study of HIV-2 came up with an origin for the main group be- tween 1940 and 1945.

Another objection to the OPV the- ory concerns the subspecies of chim- panzee kept near Kisangani (formerly Stanleyville) at a facility called Camp Lindi, which Koprowski and colleagues maintain was used for safety-testing their vaccine, but which Hooper sus- pects was the source of chimpanzee tis- sues used to produce vaccine locally. The SIVcpz strain that is most similar to HIV-1 has so far only been identified in a subspecies of chimpanzee native to west-central Africa, Pan troglodytes trog- lodytes. A second, less similar strain has been identified only in Pan troglodytes schweinfurthii, the subspecies found in east-central Africa—where Camp Lindi was located. The nearest known popu- lations of P. t. troglodytes are more than 500 kilometers from Koprowski’s chimp colony. So, this argument goes, the local- ly obtained captive chimps would not

Figure 2. One controversial theory posits that the transfer of the chimpanzee immunodeficiency virus to human beings took place between 1957 and 1960 in the course of an oral polio-vaccination campaign carried out by Ghislain Courtois, Hilary Koprowski and their colleagues in what are now the Democratic Republic of the Congo, Burundi and Rwanda. This sign from the chimpanzee colony maintained in connection with that campaign reads, “Polio mission of Courtois-Koprowski, experi- mentation center, entrance forbidden.” (Photograph by Gilbert Rollais, courtesy of Edward Hooper.)

have been carrying the SIVcpz strain thought to have given rise to HIV-1.

One difficulty with this argument is that distance is not always measured in kilometers, particularly in Central Afri- ca: Kisangani lies at the upstream end of the navigable portion of the Congo Riv- er, which borders the range of P. t. trog- lodytes for hundreds of kilometers, and river trade has been substantial since the colonial scramble for Africa in the late 19th century. If it became known that Americans were paying good money for young apes in Kisangani, it would be almost surprising if some hunters had not made the trip upriver. Anoth- er problem is the difficulty of proving the absence of something based on only a few samples, which requires some significant assumptions about the

epidemiology of SIVcpz in the wild. In short, although the majority of the

biological evidence published in the last few years suggests that the OPV hypoth- esis is wrong, headlines reporting the death of this theory remain premature.

Theory 2: Cut Hunter The main competing theory posits that SIV is occasionally transmitted to hunters via blood-to-blood contact with an infected primate. Accord- ing to this view, the virus is usually cleared in its human host, but at least several times during the 20th century it survived and became established as HIV. It is not hard to imagine hunters suffering cuts or being injured by a wounded mangabey or chimpanzee, and some form of natural transfer be-

tween species presumably accounts for the widespread distribution of SIVs in African primates. Hence, one has the “cut hunter” or “natural transfer” theory, which is probably the most ac- cepted idea today. According to that view, the timing of the widespread emergences of HIV-1 and HIV-2 in the middle part of the 20th century is at- tributed to urbanization and regional commerce, which create conditions ideal for spreading a sexually trans- mitted disease.

Unlike the case with OPV, there is no easy way to disprove this theory— even a smoking gun linking oral po- lio vaccines to HIV-1 group M would leave multiple other HIV strains unac- counted for, and “modernization” is a diffuse enough explanation to cover

Dakar

Kinshasa (Leopoldville)

NairobiKisangani (Stanleyville)

5 (1976)

2 (1980/81)

DEMOCRATIC REPUBLIC

OF THE CONGO

Co ngo Rive r

RWANDA BURUNDI

8 (1980/81)16 (1980/81)

3 (1980/81)

KENYA

SENEGAL

9 (1981)

1 (1981)

African trials of CHAT vaccine 1957–1960

Burundi, unspecified CHAT vaccination sites

number (and date) of confirmed HIV-1 infections in Africa through 1981

range of Pan troglodytes troglodytes

range of Pan troglodytes schweinfurthii

1 (1959) 2 (1970) 1 (1975) 1 (1978)

16 (1980) 1 (1978)

1 (1977)

1 (1977) 1 (1976)

Figure 3. “CHAT” oral polio vaccine was fed to approximately one million people at various sites (red dots and pink zone) between 1957 and 1960. The degree of correspondence between these locales and early evidence of HIV-1 infection in Africa through 1981 (squares) is striking. The evidence comes either from patients who showed symptoms of AIDS and who later proved to be infected with HIV-1, or from HIV-positive blood samples taken at the time. (Note that two confirmed AIDS cases are not shown: a patient who acquired the virus somewhere in Tanzania before 1981, and one who acquired a form of the virus that is genetically distinct from the main form in either Cameroon or Kenya before 1967.) A comparison of CHAT sites and early AIDS cases that were never serologically tested (not shown) gives a similarly high degree of correspondence. Critics of the theory that this vaccination program ignited the epidemic note that the correlation between vaccination sites and early evidence of AIDS may just reflect the distribution of population centers and of medical facilities. They also point out that the SIVcpz carried by Pan troglodytes schweinfurthii (green)—the subspecies of chimpanzee found near Stanleyville (Kisangani), where those involved with the CHAT campaign maintained a colony of chimpanzees—is less closely related to HIV-1 than is the SIVcpz carried by Pan troglodytes troglodytes, which lives to the west (purple). The first criticism requires a careful statistical analysis to evaluate. The second ignores the fact that some chimpanzees might have been obtained for the colony from hunters working lower on the Congo River, which supported considerable steamer traffic at the time. (Data on CHAT sites and early HIV occurrences are from Hooper 2000. Subspecies ranges derived from Worobey et al. 2004.)

with permission only. Contact [email protected].

any of them. Nor is the cut-hunter theory particularly limited in time. Af- ter all, many Africans began moving to colonial capitals and ports in the 19th century. A hypothesis that does not account for the timing of the AIDS epidemic and that is not falsifiable is of limited use. Still, the thinness of the theory does not make it wrong

Theory 3: Contaminated Needles The next proposal, a refinement of the cut-hunter theory, comes from Preston A. Marx, a virologist who holds posi- tions at Tulane University and at the Aaron Diamond AIDS Research Center. In 1995 he noted (to Hooper) that a big change in medical practice took place in the 1950s with the worldwide introduc- tion of disposable plastic syringes, mak- ing guaranteed sterile use possible and dropping the cost of syringe production by almost two orders of magnitude. The result was that the medical use of injec- tions went up astronomically. Because doses can be measured and there is no possibility of patients losing or selling the medicine, injections became a popu- lar way for doctors in the developing world to administer medicines, includ- ing vitamins, analgesics and other com- mon drugs.

The problem is that trivial costs are still large to someone living outside the cash economy, and plastic syringes cannot be sterilized by boiling: they melt. According to this scenario, the widespread availability of disposable syringes increased the acceptance of

injections to treat a variety of diseases, but the syringes were not so available (or cheap) as to permit users actually to dispose of them. The result was that unsterilized syringes were used again and again, spreading viruses, including those that eventually be- came HIV.

Marx suggests that people’s immune systems would normally be able to over- come an SIV they acquired, say while butchering a monkey, within a week or two of infection. He further posits that the transition from SIV to HIV demands a series of mutations, with the probability of all the required mutations occurring being a function of viral population size. Thus, Marx contends, some way must be found to permit the SIV to remain at high levels in people for long enough that such spontaneous mutations might take place. He suggests that the required mechanism is “serial passaging” of virus through unsterile needles. That is, a cut hunter might get an injection while he is still har- boring large numbers of viral particles in his bloodstream; that same needle would then be used to infect another person, who might soon receive a second injec- tion, and so forth. High viral population levels can thus be maintained in a series of different people getting shots. With each transfer via contaminated needle, the virus finds itself in a fresh host, with an opportunity to proliferate before the infected person can mount an immune response. Chance mutations can thus ac- cumulate, and eventually the SIV adapts, becoming HIV.

Theory 4: Heart of Darkness Together with two undergraduate students, I am responsible for another variant to the cut-hunter theory, so perhaps I should explain how I be- came engaged in this field of inquiry. In late 1998 I became involved in an

Figure 5. Because the cut-hunter theory alone fails to explain the timing of the AIDS epi- demic, investigators have looked for other factors that might hold the key. One is the widespread distribution of disposable sy- ringes, which began in the 1950s. Although inexpensive, these devices proved too pre- cious to be thrown out in many poor parts of the world. And unlike the metal or glass units that they replaced, plastic syringes can- not be sterilized by boiling them (they melt). The result is that unsterilized syringes were often reused, spreading disease. Even now, such problems are common in the develop- ing world, as can be seen in the proportion of health centers in selected African countries where syringes or needles are reused without sterilization. (Data from Dicko et al. 2000.)

Figure 4. SIV may have crossed the species barrier to humans in the course of someone killing a chimpanzee or monkey for meat. At left, Efe Pygmy hunters of the Ituri Forest, Democratic Republic of the Congo, butcher a mangabey killed with bow and arrow. At right, a hunter from Sierra Leone uses a more modern weapon (a shotgun) to kill mangabeys. (Photograph at left by Heidi Verhoef, courtesy of the Bushmeat Crisis Task Force, www.bushmeat.org. Photograph at right courtesy of Glyn Davies, Zoological Society of London.)

0 20 40 60 80 100

Swaziland 1998

Uganda 1998

Côte d’Ivoire 1997

Chad 1997

proportion of health centers re-using syringes or needles

without sterilization (percent)

e-mail discussion about the conser- vation implications of the identifica- tion of central African chimpanzees as the source of HIV-1, a result that Beatrice H. Hahn of the University of Alabama at Birmingham and her col- leagues had just published. At about the same time, a colleague urged me to read King Leopold’s Ghost, Adam Hoch- schild’s history of the Belgian Congo, and I was independently contacted by two students, Amit Chitnis and Diana Rawls, who were interested in doing something involving the intersection of biological anthropology and medi- cine. Then came the catalyst: an article in Discover magazine that mentioned the idea that the origin of AIDS might have had something to do with the chaos that followed colonial with- drawal from central Africa. The notion was that the colonial authorities had kept things under control, but when they left, “there was a free-for-all” that provided the conditions for the estab- lishment of a new disease.

King Leopold’s Ghost had more impact on me than any other book I have read. I had vaguely heard that Belgian rule was harsh, but I had not realized that more Africans probably died as a result of colonial practices in French Equatorial Africa and neighboring Belgian Congo between 1880 and the onset of World War II than had been taken from Africa as slaves during the preceding 400 years. “Probably,” because no record was kept of the dead. The first censuses, taken in the 1920s, estimated that the popula- tion of the two colonies was then about 15 million. Census-takers recorded that wherever they asked, local people (co- lonial and native) reported that about twice as many had lived there two or three decades before, indicating that some 15 million had died. Losing 50 percent of the population exceeds even the 35-percent fatality rate of the Black Death in Europe.

It seems Joseph Conrad’s Heart of Darkness was as much fact as fiction, and the horror described in that fa- mous novel reflected official policies in the Congo as much as individual insanity. What appeared to many as colonial “control” of the region in the late 19th and early 20th centu- ries brought chaos to the lives of the Africans who lived and died under it. Chitnis, Rawls and I set out to see what disease-promoting factors might have existed prior to the withdrawal of colonial powers around 1960.

Candidates were not difficult to find, at least during the years prior to World War I. Forced labor camps of thousands had poor sanitation, poor diet and ex- hausting labor demands. It is hard to imagine better conditions for the estab- lishment of an immune-deficiency dis- ease. Where imagination fails, let history serve. To care for the health of the labor- ers, well-meaning but undersupplied doctors routinely inoculated workers against smallpox and dysentery, and they treated sleeping sickness with se-

rial injections. The problem is, the mul- tiple injections given to arriving gangs of tens or hundreds were administered with only a handful of syringes. The im- portance of sterile technique was known but not regularly practiced: Transfer of pathogens would have been inevitable. And to appease the laborers, in some of the camps sex workers were officially encouraged.

And that was just the situation in the camps. Major efforts were made to erad- icate smallpox and sleeping sickness

Figure 6. Another modification of the cut-hunter theory suggests that the widespread brutalization of natives of the Congo basin during the colonial era promoted both the adaptation of SIVcpz to humans (its transformation to HIV-1) and the initial spread of the virus. In particular, people living in this region suffered enormously, many being forced to extract ivory and rubber from the jungle. King Leopold II of Belgium came under intense international scrutiny as a result of his harsh treatment of those living in the Congo Free State. This drawing, which appeared in the magazine Punch in 1906, shows a native man ensnared by a serpent with the head of King Leopold.

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with permission only. Contact [email protected].

elsewhere in the region (these diseases cut into productivity). The shortage of syringes was acute. One 1916 sleep- ing-sickness control expedition treated 89,000 people in Ubangi Shari (now Central African Republic) using just six syringes. And before the introduction of dried smallpox vaccine in about 1914, the only way to transport vaccine to the interior was by serially inoculating people, traveling during the eight-day interval required for the new carrier to develop pustules from which the next inoculation could be derived. There are records of at least 14,000 people receiv- ing vaccine in this way. The method had been abandoned in Europe some 20 years before, because syphilis was all-too-often transmitted accidentally in the process.

Such circumstances easily could have promoted the evolution of HIV from SIVcpz. Imagine, for example, the fol- lowing scenario:

A fisherman flees his small village to es- cape a colonial patrol demanding its rub- ber quota; as he runs, he grabs one of the unfamiliar shotguns recently arrived in the area. While hiding for several days, he shoots a chimpanzee and, unfamiliar with the process of butchering it, is infected with SIVcpz. On return to the village he finds his family massacred and the village

disbanded. He wanders for miles, dodging patrols, until arriving at a distant village. The next day he is seized by a railroad press gang and marched for days to the labor site, where he (along with several hundred oth- ers) receives several injections for reasons he does not understand. During his months working on the railroad, he has little to eat and is continually stressed, susceptible to any infection. He finds some solace in one of the camp prostitutes (themselves imported by those in charge), but eventually dies of an undiagnosed wasting—the fate of hun- dreds in that camp alone. Disease, starva- tion, abuse—no record is kept, none of the authorities knows, and those few doctors who care are overwhelmed.

We wrote up a short article laying out reasons to at least examine colonial- era practices seriously in regard to how they may have contributed to the origin and spread of HIV. It probably would have been ignored but for another co- incidence: Our paper appeared in the journal AIDS Research and Human Retro- viruses almost simultaneously with the report of Korber and her colleagues in Science placing the beginnings of HIV-1 Group M in the early decades of the 20th century. If this dating is correct, the colo- nial-policy theory offers an explanation. Note, however, that a version of the ba- sic cut-hunter theory that does not rely

Figure 8. Until his death in 2000, William D. Hamilton, a renowned evolutionary biolo- gist at the University of Oxford, was the most prominent scientist expressing support of the OPV theory. He died as an indirect result of malaria acquired in the Congo, where he and two coworkers were collecting material to probe the detailed nature of simian immunode- ficiency viruses in a region where chimpanzees were obtained in conjunction with the polio- vaccination campaigns of Koprowski and his colleagues. This photograph shows Hamilton in the field during his final expedition.

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Figure 7. Different theories point to different events as crucial to the genesis of the AIDS epidemic. The colonial-disruptions theory emphasizes goings-on in the early part of the 20th century, whereas the contaminated-needle theory places the spark after 1950. The controversial theory at- tributing the epidemic to an experimental polio-vaccination campaign carried out between 1957 and 1960 falls closest in time to the first confirmed HIV-positive blood sample, taken in 1959 from someone living in Leopoldville (Kinshasa). The number of people infected with HIV has since risen to almost 40 million. (Data on rise in HIV infections from UNAIDS.)

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on urbanization (or sets a much lower threshold for the critical level of city life) could also explain the genesis and initial spread of HIV during this period.

Neither of these scenarios neatly ac- counts for the decades between the pos- tulated origin of HIV in the early part of the 20th century and the widespread emergence of AIDS in Africa, which did not take place until the early 1980s. But maybe that long delay is only an arti- fact of our perceptions: Starting with a single case and assuming a doubling in frequency every few years, one would need decades to pass for the prevalence to build appreciably; would colonial doctors have noticed an initially rare immune disease? Nor do these theo- ries readily explain details of the spa- tial pattern in the early cases of HIV infection and AIDS, which indeed show a suggestive overlap with the sites of oral polio vaccination. But is that cor- respondence just a function of the dis- tribution of population and doctors? As with all of the current ideas, one can suggest various explanations to account for intriguing observations or troubling discrepancies. For the moment, the fit between theory and observation re- mains loose enough that no one view has proved absolutely compelling.

Battling Theories Arguments over rival theories of the origin of AIDS have raged viciously at times—far beyond the norms of most scientific debates. Indeed, both sides in the OPV controversy have in the re- cent scientific literature gone so far as to accuse their opponents of lying and manipulating evidence. I only became aware of the explosive nature of the debate after my students and I unwit- tingly wandered into this minefield.

Some of the participants in this con- troversy appear unwilling even to en- tertain the possibility of being wrong. Given the precarious status of each of the current theories, it seems more rea- sonable to try to keep an open mind until better evidence emerges and, in the meantime, to consider the litera- ture on each of these origin stories as representing a highly refined simula- tion scenario. Insofar as there is any material benefit to come from under- standing the origin of HIV in terms of cautionary tales, each model can and should be considered plausible—and worrisome. After all, unsterile needles do transmit diseases, contaminated po- lio vaccine did spread a simian virus

(one called SV40) to millions of people, doctors do sometimes conduct risky re- search, colonial policies did have major health consequences, and contact with wild animals can introduce pathogens into humans.

An obvious general lesson can be drawn from all four theories: For some very puzzling reason, the origin of HIV was not fundamentally natural, given that humans apparently failed to ac- quire an immunodeficiency virus from simians during thousands of years of exposure. Instead, the emergence of HIV involved social change in one form or another: the abuses carried out at the hand of an invading foreign power; abrupt urbanization overwhelming the ability of medical and political authori- ties to manage the process; the undersu- pervised transfer of medical technology and half-measures in development pro- grams; doctors taking liberties in dis- tributing medicines without adequate precautions. It is worth noting that three of the four theories postulate an origin for AIDS that involves the inadvertent results of medical efforts, with what were then state-of-the-art health pro- grams and technologies carrying with them unforeseen dangers.

Whether understanding the origin of HIV and AIDS is useful for evaluating risks associated with present-day con- cerns (say, the consumption of wildlife that might be the natural reservoir for emerging diseases like SARS, or evalu- ating the likelihood that the transplan- tation of animal organs into people will unleash a dangerous new virus) is a matter of opinion. My own view is that a firmer grasp of what happened in the past—and what might easily have hap- pened had circumstances been slightly different—helps society to understand these dangers and to minimize the risk of sparking the next global scourge.

Bibliography

Apetrei, C., D. L. Robertson and P. A. Marx. 2004. The history of SIVs and AIDS: Epide- miology, phylogeny and biology of isolates from naturally SIV infected non-human pri- mates (NHP) in Africa. Frontiers in Biosci- ence 9:225–254.

Chitnis, A., D. Rawls and J. Moore. 2000. Ori- gin of HIV-1 in colonial French Equatorial Africa? AIDS Research and Human Retrovi- ruses 16:5–8.

Cohen, J. 2001. Disputed AIDS theory dies its final death. Science 292:615.

Curtis, T. 1992. The Origin of AIDS. Rolling Stone issue 626 (19 March):54–59+.

Dicko, M., A.-Q. O. Oni, S. Ganivet, S. Kone, L.

Pierre and B. Jacquet. 2000. Safety of im- munization injections in Africa: Not simply a problem of logistics. Bulletin of the World Health Organization 78:163–169.

Hochschild, A. 1998. King Leopold’s Ghost: A Sto- ry of Greed, Terror, and Heroism in Colonial Af- rica. New York, Boston: Houghton Mifflin.

Hooper, E. 2000. The River: A Journey to the Source of HIV and AIDS. Boston: Back Bay Books.

Hooper, E. 2003. Dephlogistication, imperi- al display, apes, angels, and the return of Monsieur Émile Zola: New developments in the origins of AIDS controversy, includ- ing some observations about ways in which the scientific establishment may seek to limit open debate and flow of information on “difficult” issues. Atti dei Convegni Lincei 187:27–230.

Korber, B., M. Muldoon, J. Theiler, F. Gao, R. Gupta, A. Lapedes, B. H. Hahn, S. Wolin- sky and T. Bhattacharya. 2000. Timing the ancestor of the HIV-1 pandemic strains. Sci- ence 288:1789–1796.

Kyle, W. S. 1992. Simian retroviruses, polio- vaccine, and origin of AIDS. The Lancet 339:600–601.

Lemey, P., O. G. Pybus, B. Wang, N. K. Sakse- na, M. Salemi and A.-M. Vandamme. 2003. Tracing the origin and history of the HIV-2 epidemic. Proceedings of the National Acad- emy of Sciences of the U.S.A. 100:6588–6592.

Peeters, M., V. Courgnaud, B. Abela, P. Au- zel, X. Pourrut, F. Bibollet-Ruche, S. Loul, F. Liegeois, C. Butel, D. Koulagna, E. Mpoudi- Ngole, G. M. Shaw, B. H. Hahn and E. Dela- porte. 2002. Risk to human health from a plethora of simian immunodeficiency vi- ruses in primate bushmeat. Emerging Infec- tious Diseases 8:451–457.

Peterson, D. 2003. Eating Apes. Berkeley: Uni- versity of California Press.

Reeler, A. V. 1990. Injections: A fatal attraction? Social Science & Medicine 31:1119–1125.

Salemi, M., K. Strimmer, W. W. Hall, M. Duffy, E. Delaporte, S. Mboup, M. Peeters and A.- M. Vandamme. 2001. Dating the common ancestor of SIVcpz and HIV-1 group M and the origin of HIV-1 subtypes using a new method to uncover clock-like molecular evolution. The FASEB Journal. 15:276–278.

Weiss, R. A. 2001. Polio vaccines exonerated. Nature 410:1035–1036.

Worobey, M., M. L. Santiago, B. F. Keele, J.-B. N. Ndjango, J. B. Joy, B. L. Labama, B. D. Dhed’a, A. Rambaut, P. M. Sharp, G. M. Shaw, B. H. Hahn. 2004. Contaminated po- lio vaccine theory refuted. Nature 428:820.

For relevant Web links, consult this issue of American Scientist Online:

http://www.americanscientist.org/ IssueTOC/issue/661

__MACOSX/._Moore The Puzzling Origins of AIDS (2).pdf

Mukhopadhyay and Henze (1).pdf

MAY 2003 669

S URELY WE’VE all heard people say there is only one race — the human race. We’ve also heard and seen overwhelming evidence that would seem to contradict this view. After all, the U.S. Census di- vides us into groups based on race, and there are c e rtainly observable physical differences among p e o p l e — skin color, nose and eye shape, body type, hair color and texture, and so on. In the world of

education, the message of racial differences as biological “f a c t s” is re- i n f o rced when we are told that we should understand specific learn- ing styles and behavior patterns of black, Asian, Native American, white, and Latino children and when books such as The Bell Cu rve make pseudoscientific claims about race and learning.1

How can educators make sense of these conflicting messages about race? And why should they bother? Whether we think of all human beings as one

race, or as four or five distinct races, or as hundreds of races, does anything really change? If we accept that the con- cept of race is fundamentally flawe d , does that mean that young African Americans are less likely to be followe d by security guards in department store s ? A re people going to stop thinking of Asians as the “m o d e l” minority? Wi l l racism become a thing of the past?

How Real Is Race? Using Anthropology to Make Sense Of Human Diversity Race is not a scientifically valid biological category, and yet it re m a i n s i m p o rtant as a socially constructed category. Once educators grasp this concept, they can use the suggestions and re s o u rces the authors off e r h e re to help their students make sense of race.

BY CAROL MUKHOPADHYAY AND ROSEMARY C. HENZE

CAROL MUKHOPADHYAY is a professor in the Department of Anthropology, San José State University, San José, Calif., where ROSEMARY C. HENZE is an associate pro- fessor in the Department of Linguistics and Language Development. They wish to thank Gilberto Arriaza, Paul Erickson, Alan Good- man, and Yolanda Moses for their comments on this article.

670 PHI DELTA KAPPAN

Many educators understandably would like to have clear information to help them teach students about hu- man biological va r i a b i l i t y. While mul- ticultural education materials are now widely available, they rarely address basic questions about why we look dif- f e rent from one another and what these biological differences do (and do not) mean. Multicultural education empha- s i zes respecting differences and finding ways to include all stu- dents, especially those who h a ve been historically mar- g i n a l i zed. Multicultural ed- ucation has helped us to un- derstand racism and has pro- vided a rich body of litera- ture on antiracist teaching strategies, and this has been all to the good. But it has not helped us understand the two concepts of race: the biological one and the social one.

In this article, we explain what anthropologists mean when they say that “races don’t exist” (in other words, when they reject the concept of race as a scientifically valid biolog- ical category) and why they argue in- stead that “race” is a socially con- structed category. We’ll also discuss why this is such an important under- standing and what it means for edu- cators and students who face the so- cial reality of race and racism every d a y. And finally, we’ll offer some sug- gestions and resources for teachers who want to include teaching about race in their classes.

WHY RACE ISN’T B I O L O G I CA L LY REAL

For the past several decades, bio- logical anthropologists have been ar- guing that races don’t really exist, or, more precisely, that the concept of race has no validity as a biological cat-

egory. What exactly does this mean? First, anthropologists are unrav-

eling a deeply embedded ideology, a long-standing European and Amer- ican racial world view.2 Historically, the idea of race emerged in Europe in the 17th and 18th centuries, coin- ciding with the growth of colonial- ism and the transatlantic slave trade. Attempts were made to classify hu- mans into “natural,” geographically

distinct “races,” hierarchically ord e re d by their closeness to God’s original forms. Europeans were, not surpris- ingly, at the top, with the most per- fect form represented by a female skull from the Caucasus Mountains, near the purported location of No ah’s a rk and the origin of humans. He n c e the origins of the racial term “Cau- casian” or “Caucasoid” for those of European ancestry.3

In the late 19th century, anthro- pologists sought to reconstruct hu- man prehistory and trace the evolu- tion of human cultural institutions. Physical and cultural evolution were seen as moving in tandem; “advanc- es” in human mental capacity were thought to be responsible for human cultural inventions, such as marriage, family, law, and agriculture. If cul- tural “e vo l u t i o n” was propelled by bi- ological evolution, according to this logic, the more “advanced” cultures

must be more biologically and intel- lectually evo l ved. Physical indicators of evo l u t i o n a ry rank, such as skull size , were sought in order to classify and rank human groups along an evolu- tionary path from more “primitive” to more “advanced” races.

Ni n e t e e n t h - c e n t u ry Eu ropean sci- entists disagreed on when the “races” began. Theologians had long argued that there was “one human origin,”

Adam and Eve, and that certain races subsequently “d e g e n e r a t e d” (pre d i c t a b l y, the non-Eu ropeans). So m e e vo l u t i o n a ry scientists, how- e ve r, began to argue for mul- tiple origins, with distinct races evolving in different places and times. By the be- ginning of the 20th century, Eu ropean and American sci- ence viewed races as natural, long-standing divisions of the human species, evolv- ing at different rates bio-

logically and hence culturally. By such logic was racial inequality naturalize d and legitimized.

When contemporary scientists, in- cluding anthropologists, assert that races are not scientifically valid, they a re rejecting at least three fundamen- tal premises of this old racial ideol- ogy: 1) the archaic subspecies concept, 2) the divisibility of contemporary humans into scientifically valid bio- logical groupings, and 3) the link be- t ween racial traits and social, cultur- al, and political status.

1. There were no distinct, archaic human subspecies. The first premise a n t h ropologists reject is that humans we re originally divided, by nature or God, into a small set of biologically distinct, fixed species, subspecies, or races. Anthropologists now know con- clusively, from fossil and DNA evi- dence, that contemporary humans are one variable species, with our roots

For the past several decades, biol o g i c a l

a n t h ropologists have been a rguing that the concept of

race has no validity as a biological category.

MAY 2003 671

in Africa, which moved out of Africa into a wide range of environments around the world, producing hun- d reds, perhaps thousands, of cultur- ally and genetically distinct popula- tions. Local populations, through nat- ural selection as well as random ge - netic mutation, acquired some dis - t i n c t i ve genetic traits, such as shove l - shaped incisor teeth, hairy ears, or re d h a i r. Adaptation to human cultural in- ve n t i o n s — such as agriculture, which creates concentrations of water that allow malaria-carrying mosquitoes to bre e d — also produced higher fre- quencies of sickle-cell genes (related to malaria resistance) in human pop- ulations in some parts of Africa, In- dia, Arabia, and the Me d i t e r r a n e a n .4

At the same time, continuous migra- tion and intermating between local pop- ulations pre vented us from branching off into distinct subspecies or species and instead created a richer and more variable gene pool, producing new combinations and permutations of the human genome.

Human pre h i s t o ry and history, then, are a continuing story of fusion and fission, of a myriad of populations, emerging and shifting over time and space, sometimes isolated temporari- l y, then fusing and producing new for- mations. There have been thousands and thousands of groups thro u g h o u t

human history, marrying in and, more often, out; they have disappeared and reemerged in new forms over time.

In short, there are no “basic” or “ancient” races; there are no stable, “natural,” permanent, or even long- standing groupings called races. T h e re h a ve never have been any “p u re” races. All human populations are histori- cally specific mixtures of the human gene pool. This is human evolution, and we see these same processes at work in the 19th and 20th centuries and today. “Races” are ephemeral — here today, gone tomorrow.

2. Contemporary humans are not divisible into biological races. When anthropologists say races aren’t bio- logically real, they also reject the idea that modern humans can be divided into scientifically valid, biologically distinct groupings or races. For races to be real as biological categories, the classification must be based on ob- jective, consistent, and reliable bio- logical criteria. The classification sys- tem must also have predictive value that will make it useful in research.

Scientists have demonstrated that both the concept of race and racial criteria are subjective, arbitrary, and inconsistently applied.5 U.S. racial categories, such as the ones used in the Census, aren’t valid in part be- cause the biological attributes used to

define races and create racial classi- fications rely on only a few visible, su- p e rficial, genetic traits — such as skin color and hair texture — and ignore the remaining preponderance of hu- man variation. Alternative, equally vis- ible racial classifications could be con- s t ructed using such criteria as hair col- o r, e ye color, height, weight, ear shape, or hairiness. However, there are less visible genetic traits that have far gre a t- er biological significance. For exam- ple, there are at least 13 genetic factors related to hemoglobin, the protein that helps carry oxygen to tissues, and there is also significant variation in the ABO, RH, and other blood systems. We could create racial classifications based on genetic factors that affect susceptibil- ity to diabetes or to certain kinds of breast cancer or to the ability to di- gest milk. In sum, given the variety of possible biologically based traits for classifying human beings, the cri- teria used in U.S. racial categorizations are highly arbitrary and subjective. Our discussion here focuses on the U.S. concept of race. While racial con- cepts a re no doubt similar in Canada and Eu rope, this is not true in other parts of the Americas.6

The number of potential biolog- ically based racial groupings is enor- mous. Not only are there millions of

672 PHI DELTA KAPPAN

genetic traits, but most genetic traits — even culturally salient but super- ficial traits such as skin color, hair tex- t u re, eye shape, and eye color — do not cluster together. Darker skin can cluster with straight hair as well as with very curly hair or with hairy or nonhairy bodies; paler skin can clus- ter with straight or curly hair or with black or blond hair or with lighter to darker eyes. Each trait could pro- duce a different racial classification. For example, if one used height as a criterion rather than skin pigmenta- tion, then the No rthern Afghan pop- ulation would be in the same racial c a t e g o ry as the Swedes and the Tu t s i of Rwanda. There are huge numbers of genetically influenced traits, visi- ble and nonvisible, which could be used to classify humans into biolog- ically distinct groups. T h e re is no “n a t- u r a l” classification — no co-occurring clusters of racial traits. T h e re are just alternatives, with different implica- tions and uses.

Racial classifications are also un- scientific because they are unre l i a b l e and unstable over time. Individuals cannot reliably be “raced,” partly be-

cause the criteria are so subjective and unscientific. Robert Hahn, a medi- cal anthropologist, found that 37% of babies described as Native Ameri- can on their birth certificates ended up in a different racial category on their death certificates.7 Racial iden- tifications by forensic anthro p o l o g i s t s , long touted as accurate, have been shown to be disturbingly unreliable, e ven in re l a t i vely ethnically homo- geneous areas, such as Missouri and Ohio.8 Forensic evidence from such urban areas as San José, California, or New Yo rk City is even more pro b- l e m a t i c .

Racial categories used by the U.S. Census Bureau have changed over time. In 1900, races included “mu- latto, quadroon, or octoroon” in ad- dition to “black.” Southern Eu ro p e a n s and Jews we re deemed to be separate races before World War II. Asian In- dians (“Hindus”) were initially cate- g o r i zed as “Caucasoid” — e xcept for voting rights. The number and defi- nitions of races in the most recent U.S. Census reflect the instability — and hence unre l i a b i l i t y — of the con- cept of race. And U.S. racial classifi-

cations simply don’t work in much of the rest of the world. Brazil is a clas- sic, often-studied example, but they also don’t work in South Asia, an are a that includes over one-fifth of the world’s population.

Historical and contemporary Eu- ropean and American racial categories a re huge, biologically diverse macro - categories. Members of the same ra- cial group tend to be similar in a few genetic ways that are often biologi- cally irre l e vant. Mo re ove r, the genet- ic variability found within each ra- cial grouping is far greater than the genetic similarity. Africa, by itself, is home to distinct populations whose average height ranges from less than five feet (the Mbuti) to over six feet (the Tutsi). Estimates suggest that con- temporary racial variation accounts for less than 7% of all human genet- ic va r i a t i o n .9 U.S. races, then, are not biologically distinct or biologically m e a n i n gful, scientifically based gro u p- ings of the human species.

3. Race as biology has no scientific value. An additional critique of the concept of race is that racial cate- gories, as defined biologically, are not

MAY 2003 673

very useful in understanding other phenomena, whether biological or cul- t u r a l .

T h e re is no substantial evidence that race, as a biological category, and “r a- c i a l” characteristics, such as skin col- or, hair texture, and eye shape, are causally linked to behavior, to capac- ities, to individual and group accom- plishments, to cultural institutions, or to propensities to engage in any spe- cific activities. In the area of academ- ic achievement, the focus on race as biology can lead re s e a rchers to ignore underlying nonbiological causal fac- tors. One classic study found that con- t rolling for socioeconomic and other environmental variables eliminated p u r p o rted “r a c i a l” differences in I.Q. s c o res and academic achievement be- tween African American, Mexican American, and European American students.10

Health professionals have also cri- tiqued the concept of race. Alan Go o d- man and others have shown that race does not help physicians with diagno- sis, prevention, or treatment of med- ical diseases.11 Racial categories and a false ideology of race as “biology” encourage both doctors and their pa- tients to view medical conditions as necessarily genetic, ignoring possible e n v i ronmental sources. Hy p e rt e n s i o n , infant birt h weights, osteoporosis, ova r- ian c y s t s — all traditionally viewed as “r a c i a l” (i.e., genetically based) — n ow seem to reflect environmental rather than racially linked genetic factors. The Centers for Disease Control con- cluded in 1993 that most associations between race and disease have no ge- netic or biological basis and that the concept of “r a c e” is there f o re not use- ful in public health.

As a result of recent evolution and constant interbreeding between gro u p s of humans, two individuals from dif- f e rent “races” are just as likely to be m o re similar to one another genetic-

ally than two individuals from the same “race.” This being so, race-as- biology has no predictive value.

IF NOT RACE, THEN WHAT?

Classifications are usually created for some purpose. Alan Goodman and other biological anthro p o l o g i s t s suggest that investigators focus on using traits relevant to the problem at hand. For example, if a particular blood factor puts an individual at risk for a disease, then classify indi- viduals on that basis for that purpose.

Some suggest using the term “p o p- u l a t i o n” or “breeding population” to refer to the multitude of small, often geographically localized, groups that have developed high frequencies of one or more somewhat distinctive bi- ological traits (e.g., shovel-shaped in- cisors) in response to biological, his- torical, and cultural factors. But oth- ers point out that there could be thou- sands of such groups, depending on the classifying criteria used, and that the groups would be merging and re- combining over time and space. Mo re- ove r, the variability “c a p t u re d” would reflect only a fraction of the va r i a b i l- ity in the human species.

Most anthropologists now use the concept of “c l i n e s” to help understand how genetic traits are distributed.12

New data indicate that biological traits, such as blood type or skin color, are distributed in geographic gradations or “clines”; that is, the frequency of a trait varies continuously over a geo- graphic area. For example, the genes for type B blood increase in fre q u e n- cy in an east-to-west direction (re- flecting, in part, the travels of Gen- ghis Khan and his army). In contrast, skin pigmentation grades from nort h to south, with increasing pigmenta- tion as one gets closer to the equator. The frequency of the gene for sickle cell decreases from West Africa mov-

ing northeast. Vi rtually all traits have distinct geo-

graphic distributions. Genes contro l- ling skin color, body size and shape (head, limbs, lips, fingers, nose, ears), hairiness, and blood type are each dis- tributed in different patterns over ge- ographic space. Once again, for bio- logical races to exist, these traits would have to co-vary, but they don’t. In- stead, biological traits produce a near- ly infinite number of potential races. This is why anthropologists conclude that there are no scientifically distin- guishable biological races — only thou- sands of clines!

SO WHAT IS RACE THEN?

We hope we have made the point that the concept of separate, biolog- ically distinct human races is not sci- entifically defensible. Unfortunate- ly, racial ideology, by focusing on a few physical attributes, traps us in- to a discourse about race as biology rather than race as a cultural constru c- tion. The concept of race is a cultural i n vention, a culturally and historical- ly specific way of thinking about, cat- egorizing, and treating human beings.1 3

It is about social divisions within so- c i e t y, about social categories and iden- tities, about power and privilege. It has been and remains a particular type of ideology for legitimizing social in- equality between groups with differ- ent ancestries, national origins, and histories. Indeed, the concept of race is also a major system of social iden- tity, affecting one’s own self-percep- tion and how one is perc e i ved and tre a t- ed by others.

But race does have a biological com- ponent, one that can trick us into think- ing that races are scientifically valid, biological subdivisions of the human species. As noted earlier, geographic- ally localized populations — as a re s u l t of adaptation, migration, and chance

674 PHI DELTA KAPPAN

— tend to have some characteristic physical traits. While these may be traits that characterize an entire pop- ulation, such as hairy ears, it is more accurate to talk about the re l a t i ve fre- quency of a particular trait, such as blood type O, in one population as compared to another, or the relative amount of pigmentation of individu- als in a population, relative to other populations. Some traits, such as skin color, reflect climatic conditions; oth- ers, such as eye color and shape, probably reflect ran- dom, historical processes and migration patterns. T h e U.S. was peopled by pop- ulations from geographic- ally distinct regions of the w o r l d — vo l u n t a ry immi- grants, forced African slave s , and indigenous American groups. Therefore, domi- nant northwestern Euro- pean ethnic groups, such as the English and Germans, were able to exploit certain visually salient biological traits, especially skin color, as markers of race.

The effectiveness of these physi- cal traits as markers of one’s race de- pended, of course, on their being pre- s e rved in future generations. So dom- inant cultural groups created elabo- rate social and physical barriers to mating, reproduction, and marriage that crossed racial lines. The most ex- plicit were the so-called anti-misce- genation laws, which outlawed sex between members of different races, whether married or not. These laws were not declared unconstitutional by the U.S. Supreme Court until the 1967 case of L ov i n g v. Vi r g i n i a.1 4 A n- other vehicle was the cultural defini- tion of kinship, whereby children of interracial (often forced) matings ac- q u i red the racial status of their lowe r - ranking parent; this was the so-called

o n e - d rop rule or hypodescent. Espe- cially during the time of slavery, the lower-ranking parent was generally the mother, and thus the long-stand- ing Eu ropean cultural tradition of af- filiating socially “legitimate” childre n with the father’s kinship group was effectively reversed.

In contrast, there have been few- er social or legal barriers in the U.S.

to mating and marriage between It a l- ians, British, Germans, Swedes, and others of European ancestry. Con - sequently, the physical and cultural characteristics of European region- al populations are less evident in the U.S. With intermarriage, distinct Eu- ropean identities were submerged in the culturally re l e vant macroracial cat- e g o ry of “w h i t e” — m o re accurately, European American.

Thus even the biological dimen- sion of contemporary racial gro u p i n g s is the result of sociocultural process- es. That is, humans as cultural beings first gave social significance to some physical differences between groups and then tried to perpetuate these “r a- cial mark e r s” by pre venting social and physical intercourse between mem- bers of the groups. Although the dom- inant racial ideology was about main- taining racial “purity,” the issue was

not about biology; it was about main- taining social, political, and econom- ic privilege.15

WHY IS THIS UNDERSTA N D I N G I M P O RTANT FOR EDUCATO R S ?

We hope we’ve convinced you that race isn’t biologically “real” and that race in the U.S. and elsewhere

is a historical, social, and cultural creation. But so what? What is the signifi - cance of this way of view- ing race for teachers, stu- dents, and society?

1 . The potential for change. First, it is important to un- derstand that, while races a re biological fictions, they a re social realities. Race may not be “re a l” in a biological sense, but it surely is “re a l” s o c i a l l y, politically, econom- i c a l l y, and psyc h o l o g i c a l l y. Race and racism pro f o u n d- ly s t ru c t u re who we are, how

we are treated, how we treat others, and our access to re s o u rces and rights.

Perhaps the most important mes- sage educators can take from the fore- going discussion is that race, racial classifications, racial stratification, and other forms of racism, including ra- cial ideology, rather than being part of our biology, are part of our cul- ture. Like other cultural forms, both the concept of race and our racial clas- sifications a re part of a system we have created. This means that we have the ability to change the system, to trans- form it, and even to totally eradicate it. Educators, in their role as trans- mitters of official culture, are partic- ularly well poised to be active change agents in such a transformation.

But how, you may well ask, can teachers or anybody else make peo- ple stop classifying by race? And are t h e re any good reasons to do so? T h e s e

Race, racial c l a s s i f i c a t i o n s, racial stratification, and other

forms of racism, including racial ideology, rather than

being part of our biology, are part of our culture.

MAY 2003 675

familiar categories — black, white, Asian, Native American, and so on — seem so embedded in U.S. socie- t y. They seem so “natural.” Of course, t h a t’s how culture works. It seems “n a t- u r a l” to think of chicken, but not rats, as food. But, as we have shown above , the labels and underlying constructs that we use to talk about human di- versity are unstable, depending on par- ticular social, political, and historical contexts. Individuals in positions of a u t h o r i t y, of course, have the ability to change them institutionally. But o rd i n a ry people also have the ability to change how they classify and label people in their everyday lives.

Se veral questions arise at this point. Do we as educators consciously want to change our way of conceptualiz- ing and discussing human biological variation? What makes the “race as biology” assumption so dangerous? A re we going to continue to classify people by race, even while recogniz- ing that it is a social construct? What vested interests do people have in hold- ing o n t o — or re j e c t i n g — racial cat- egories? How can we become more sophisticated in our understanding of how systems of classification work while also becoming more critical of our own ways of classifying people? Are there alternative ways of think- ing about, classifying, and labeling human beings that might be more em- powering for students, teachers, and community members? By eliminat- ing or changing labels, will we change the power stru c t u res that perpetuate privilege and entitlement? Moving be- yond race as biology forces us to con- front these and other issues.

2. The dangers of using racial clas- sifications. Categories and classifica- tions are not intrinsically good or bad. People have always grouped others in ways that were important within a given society. However, the myth of race as biology is dangerous because

it conflates physical attributes, such as skin color, with unrelated qualities, such as intelligence. Racial labels de- lude people into thinking that race p redicts such other outcomes and be- haviors as achievement in sports, mu- sic, or school; rates of employment; p regnancies outside marriage; or dru g use. Race was historically equated with intelligence and, on that basis, was used to justify slave ry and education- al discrimination; it later provided the rationale that supported the genocide of Jews, blacks, Gypsies, and other “ i n f e r i o r” races under Hi t l e r. So using racial categories brings along this his- t o ry, like unwanted baggage.

Ma c roracial categories are danger- ous in that the categories ove r s i m p l i- fy and mask complex human differ- ences. Saying that someone is Asian tells us virtually nothing concrete, but it brings with it a host of stere o t y p e s , such as “model minority,” “quiet,” “good at math,” “inscrutable,” and so on. Yet the Asian label includes a wide range of groups, such as Kore- ans, Filipinos, and Vietnamese, with distinct histories and languages. The same is true for “white,” a term that h o m o g e n i zes the multiple nationali- ties, languages, and cultures that con- stitute Europe. The label “African A m e r i c a n” ignores the enormous lin- guistic, physical, and cultural diver- sity of the peoples of Africa. The term “black” conflates people of African descent who we re brought to the U.S. as slaves with recent immigrants fro m Africa and the Caribbean. These mac- roracial labels oversimplify and re d u c e human diversity to four or five giant g roups. Ap a rt from being bad science, these categories don’t predict anything helpful — yet they have acquired a life of their own.

Macroracial categories, such as those used in the U.S. Census and other institutional data-collection ef- f o rts, force people to use labels that

may not re p resent their own self-iden- tity or classifying system. They must either select an existing category or select “o t h e r” — by definition, a kind of nonidentity. The impossibility, un- til re c e n t l y, of selecting more than one ethnic/racial category implicitly stig- m a t i zes multiracial individuals. And the term “m i xe d” wrongly implies that t h e re are such things as “p u re” races, an ideology with no basis in science. The recent expansion of the number of U.S. Census categories still cannot accommodate the diversity of the U.S. population, which includes people whose ancestry ranges from Egypt, Brazil, Sri Lanka, Ghana, and the Do- minican Republic to Iceland and Ko- re a .

3 . How macro racial categories have s e rved people in positive ways. Ha v i n g noted some negative aspects, it is equal- ly important to discuss how macro- racial categories also serve society. Re- call that labels are not intrinsically “good” or “bad.” It depends on what people do with them. During the 1960s, the U.S. civil rights move m e n t helped bring about consciousness and pride in being African American. T h i s consciousness — known by terms such as ethnic pride and black power — united people who had been the vic- tims of racism and oppression. Fro m that consciousness sprang such edu- cational interventions as black and Chicano history classes, ethnic stud- ies departments, Afrocentric schools, and other efforts to empower yo u n g people. The movement to engender pride in and knowledge of one’s ances- t ry has had a powe rful impact. Ma n y individuals are deeply attached to these racial labels as part of a positive iden- t i t y. As one community activist put it, “Why should I give up being a race? I like being a race.”

Racial classification can also have positive impact by allowing educa- tors to monitor how equitably our

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institutions are serving the public. Racial categories are used by schools to disaggregate data on student out- comes, including achievement, atten- dance, discipline, course placements, college attendance rates, and other a reas of school and student perf o r m- ance. These data are then used to ex- amine whether certain groups of stu- dents are disproportionately repre- sented in any outcome areas. For ex- ample, a school might discover that the percentage of Latino students who receive some type of disciplinary in- t e rvention is higher than that for oth- er school populations. The school can then consider what it can do to change this outcome. Teachers might ask, Is t h e re something about the way Lati- no students are treated in the school that leads to higher disciplinary re f e r- ral rates? What other factors might be involved?

The racial classifications that ed- ucators use to monitor student out- come data reflect our society’s social c o n s t ruction of race. As such, the cat- egories re p resent groups that have been historically disenfranchised, oppre s s e d , or marginalized. Without data disag- gregated by race, gender, and other categories, it would be difficult to iden- tify problems stemming from race- based institutional and societal fac- tors that privilege certain groups, such as the widespread U.S. practice of track- ing by so-called ability. Without data broken out according to racial, gen- der, and ethnic categories, schools would not be able to assess the posi- t i ve impact intervention programs have had on different groups of students.

4 . Shifting the conversation from bi- o l o gy to culture. One function of the myth of race as biology has been to distract us from the underlying caus- es of social inequality in the United States. Dismantling the myth of race as biology means that we must now shift our focus to analyzing the social,

economic, political, and historical con- ditions that breed and serve to per- petuate social inequality. For educa- tors, this means helping students to recognize and understand socioeco- nomic stratification, who benefits and who is harmed by racial discrimina- tion, and how we as individuals and institutional agents can act to dis- mantle ideologies, institutions, and practices that harm young people.

There is another, more profound implication of the impermanence of race. Cu l t u re, acting collective l y, and humans, acting individually, can make races disappear. That is, we can mate and marry across populations, thus destroying the racial “markers” that have been used to facilitate categori- zation and differential treatment of people of different ancestry and so- cial rank. An understanding of hu- man biological variation reveals the positive, indeed essential, role that intermating and intermarriage have played in human evolution and hu- man adaptation. Rather than “mon- g re l i z i n g” a “p u re species,” mating be- t ween d i f f e rent populations enriches the genetic pool. It is society, rather than nature — and socially and eco- nomically stratified societies, for the most part — that restricts social and sexual intercourse and seve rely penal- i zes those who mate across racial and other socially created lines.

SUGGESTIONS A N D RESOURCES FOR EDUCATO R S

A n t h ropological knowledge about race informs us about what race is and is not, but it cannot guide edu- cational decision making. The under- lying goal of social justice can help educators in making policy decisions, such as whether to use racial and eth- nic categories to monitor education- al outcomes. As long as we contin- ue to see racially based disparities in

young peoples’ school achievement, then we must monitor and investi- gate the social conditions that pro- duce these disparities. We must be care- ful, however, to avoid “biologizing” the classification; that is, we must avo i d assuming genetic explanations for ra- cial d i f f e rences in behaviors and edu- cational outcomes or even diseases.

As we pursue a more socially just world, educators should also contin- ue to support young people’s quest for knowledge about the history and s t ruggles of their own people, as we l l as those of other groups, so that stu- dents in the future will not be able to point to their textbooks and say, “My people are not included in the curriculum.” In the process, we can encourage both curiosity about and respect for human diversity, and we can emphasize the importance that historical and social context plays in creating social inequality. We can al- so encourage comparative studies of racial and other forms of social strat- ification, further challenging the no- tion that there is a biological expla- nation for oppression and inequality. In short, students will understand that there is no biological explanation for a gro u p’s historical position as either oppressed — or oppressor. We can encourage these studies to point out variations and fine distinctions with- in human racial groupings.

In addition to viewing the tre a t m e n t of race and racial categories through a social-justice lens, we would apply another criterion that we call “d e p t h of knowledge.” We believe that it is important to challenge and inspire young people by exposing them to the best of our current knowledge in the sciences, social sciences, and oth- er disciplines. Until now, most stu- dents in our education system have not been exposed to systematic, sci- entifically based teaching about race and human biological variation. On e

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reason is that many social studies teach- ers may think they lack sufficient back- g round in genetics and human biol- o g y. At the same time, many biology teachers may feel uncomfortable teach- ing about race as a social construct. The null move for teachers seems to be to say that we should all be “c o l o r blind.” However, this does not help educate students about human dive r- s i t y, both biological and social. In rare cases when students have the oppor- tunity to engage in studies of race, ethnicity, culture, and ways to end racism, they are both interested and intellectually challenged.1 6 One high school teacher who teaches students about race said he wants to dispel the notion that teaching about dive r s i t y is “touchy feely.” “We don’t just want to touch diversity; we want to ap- proach it academically. . . . We feel we have a definite discipline.”17

Rather than shield students and our- s e l ves from current scientific knowl- edge about race, including its contra- dictions and controversies, we sub- mit that educators should be pro- viding opportunities for students to learn what anthropologists, geneti- cists, and other scientists, inc l u d i n g social scientists, have to say about hu- man biological variation and the is- sue of race. Particularly in midd l e schools, high schools, and beyond, students should be involved in in- q u i ry projects and social action projects, in critical examination of the labels we currently use, and in

analysis of the reasons for and against using them in particular c o n t e x t s . Rather than tell students that they should or should not use racial lab e l s ( e xcept for slurs), educators should be c reating pro jects in which students explore together the range of possi- ble ways of classifying people and the i mplications and political signifi- cance of alternative approaches in different contexts.

We would like to conclude by of- fering readers some ideas for student inquiry and by suggesting some re- sources that can serve to get teach- ers in all subject areas started on the quest to learn about human biolog- ical variation and ways to teach about it.

1. Ideas for student inquiry. Here are some examples of how teachers might engage students in critically examining the social, historical, and cultural construction of racial cate- gories.

• Have students create and em- p l oy alternative “r a c i a l” classification schemes using as many observable and nonobservable physical differe n c- es as they can think of (e.g., foot size , height, ear shape, eye b row shape, waist/ shoulder ratio, hairiness). What do the groups look like? What does this tell us about macroracial classifica- tions based on skin pigmentation and other surface features?

• Sh ow students U.S. Census forms from 1870, 1950, and 2000, and ask them to place themselves in the most

a p p ropriate category. Or show a photo- graph of a person of multiple ethnic a n c e s t ry and ask students to place this person in one of the categories from these three censuses. Ask them why they think the census form has changed over time and what that says about the meaning of “race.”

• Ask immigrant students to in- vestigate the racial/ethnic categories used in their country of origin and to reflect on how well they mesh with the U.S. categories. For example, have students from Mexico taken on an identity as Latino or Hispanic? And what does it mean for them to be- come part of a larger “macro” race in the U.S.?18

• Ask students how they feel when someone asks them to “represent their race.” For example, how do stu- dents who identify themselves as Af- rican Americans feel when s o m e o n e asks, “How do African Americans feel about this issue?” or “What’s the African American perspective on this?”

• Discuss “re verse disc r i m- ination.” When did this term come in- to use and why? Who is being dis- criminated against when discrimina- tion is reversed?

• Discuss “political correctness.” Where did this term come from? Who uses it and for what purposes? And why did it emerge?

2. Resources for teachers. The fol- l owing examples will give readers a place to start in compiling resources

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available for teaching about race. • Two major anthropological as-

sociations have produced highly re a d- able position statements on the topic of race and human biological varia- tion. First, the American Anthropo- logical Association website features both the AAA position and a sum- m a ry of testimony given in conjunc- tion with the debates on the 2000 census categories. Second, the offi- cial statement of the American Asso- ciation of Physical Anthropologists has appeared in that organization’s journal.19

• The American Anthropological Association is making a special ef- fort to disseminate understandings about race and human variation to the broader public. AnthroNotes, de- signed for precollege teachers, is a superb resource that offers concrete approaches to teaching about race, human diversity, and human evolu- tion. It is available at no charge from the Anthropology Outreach Office ( a n t h ro u t [email protected]). Se v- eral past issues of AnthroNotes treat race and ethnicity.2 0 A n t h ro p o l o g i s t s have produced materials for precol- lege teachers and teacher educators that deal with cultural diversity; some include strategies for teaching about culture and human diversity.21 Oth- ers provide useful overviews of rele- vant topics.22

• The AAA is currently engaged in a public education initiative called Understanding Race and Human Va r i- ation, which will involve a traveling museum exhibit and a website. The Fo rd Foundation has contributed one million dollars to this project.

• In 1999, the AAA created a spe- cial commission called the Anthro- pology Education Commission (AEC) to “help achieve significant progress t ow a rds the integration of anthro p o- logical concepts, methods, and issues into pre-K through community col-

lege and adult education as a means of increasing public understanding of anthropology.” The two teaching modules by Leonard Lieberman and by Lieberman and Patricia Rice, which we cited above, are available at no charge on the AEC website (www. a a a n e t . o r g / c o m m i t t e e s / c o m m i s s i o n s / aec). The AEC webpage contains ex- t e n s i ve re s o u rces that teachers can use to teach anthropological concepts and methods, including some that addre s s race.

Anthropologists recognize an ob- ligation to disseminate their knowl- edge of human biological variation and the social construction of race to the wider public. We hope that this a rticle and the re s o u rces we have pro- vided will contribute to this effort.

1. Richard Herrnstein and Charles Murray, The Bell Cu rve: Intelligence and Class St ru c t u re in Am e r- ican Life (New York: Free Press, 1994). 2. Audrey Smedley, Race in North America: Ori- gin and Evolution of a Wo rl d v i e w ( B o u l d e r, Colo. : Westview Press, 1998). 3. Jonathan Marks, Human Biodiversity: Genes, Race, and History (New York: Aldine de Gruyter, 1995). 4. Leonard Lieberman and Patricia Rice, “Races or Clines?,” p. 7, available on the Anthropolo- gy Education Commission page of the Ameri- can Anthropological Association website, www. aaanet.org/committees/commissions/aec — click on Teaching About Race. 5. George J. Armelagos and Alan H. Goodman, “Race, Racism, and Anthropology,” in Alan H. Goodman and Thomas L. Leatherman, eds., Building a New Biocultural Synthesis: Political- Economic Perspectives on Human Biology (Ann Arbor: University of Michigan Press, 1998). 6 . Je f f rey M. Fish, “Mi xed Blood,” in James Sp r a d- ley and William McCurdy, eds., Conformity and Conflict, 11th ed. (New York: Allyn & Bacon, 2002), pp. 270-80. 7. Alan Goodman, “Bred in the Bone?,” Sci- ences, vol. 37, no. 2, 1997, p. 24. 8. Ibid., p. 22. 9. Leonard Lieberman, “ ‘Race’ 1997 and 2001: A Race Odyssey,” available on the Anthropolo- gy Education Commission page of the Ameri- can Anthropological Association website, www. aaanet.org/committees/commissions/aec — click on Teaching About Race.

1 0 . Jane Me rc e r, “Ethnic Di f f e rences in IQ Scores: What Do They Mean? (A Response to Lloyd Dunn),” Hispanic Journal of Behavioral Sciences, vol. 10, 1988, pp. 199-218. 11. Goodman, op. cit. 12. Lieberman and Rice, op. cit. 13. Carol Mukhopadhyay and Yolanda Moses, “Reestablishing ‘Race’ in Anthropological Dis- course,” American Anthropologist,vol. 99, 1997, pp. 517-33. 14. Janet Hyde and John DeLamater, Under- standing Human Sexuality, 6th ed. (New York: McGraw-Hill, 1997). 15. Smedley, op. cit. 16. Karen Donaldson, Through Students’ Eyes: Combating Racism in United States Schools (We s t- p o rt, Conn.: Praeger, 1996); and Rosemary C. Henze, “Curricular Approaches to Developing Positive Interethnic Relations,” Journal of Negro Education, vol. 68, 2001, pp. 529-49. 17. Henze, p. 539. 18. Clara Rodriguez, Changing Race: Latinos, the Census, and the History of Ethnicity in the United States (New York: New York University Press, 2000); and Gilberto Arriaza, “The School Yard as a Stage: Missing Culture Clues in Sym- bolic Fighting,” Multicultural Education Jour- nal, Spring 2003, in press. 1 9 . American Anthropological Association, “A A A Statement on Race,” www. a a a n e t . o r g / s t m t s / r a c e p p. htm; and American Association of Physical An- thropologists, “AAPA Statement on Biological Aspects of Race,” American Journal of Physical Anthropology, vol. 101, 1996, pp. 569-70. 20. Alison S. Brooks et al., “Race and Ethnici - ty in America,” in Ruth O. Selig and Marilyn R. London, eds., An t h ro p o l o gy Ex p l o red: The Be s t of Smithsonian An t h ro No t e s (Washington, D.C.: Smithsonian Institution Press), pp. 315-26; E. L. Cerrini-Long, “Ethnicity in the U.S.A.: An An- thropological Model,” AnthroNotes, vol. 15, no. 3, 1993; William L. Merrill, “Identity Tr a n s f o r- mation in Colonial Northern Mexico,” Anthro- Notes, vol. 19, no. 2, 1997, pp. 1-8; and Boyce Re n s b e r g e r, “Forget the Old Labels: He re’s a New Way to Look at Race,” AnthroNotes, vol. 18, no. 1, 1996, pp. 1-7. 21. Hilda Hernandez and Carol C. Mukhopa - dhyay, Integrating Multicultural Perspectives in Teacher Education: A Curriculum Resource Guide (Chico: California State University, 1985); and Conrad P. Kottak, R. Furlow White, and Patri- cia Rice, eds. The Teaching of Anthropology: Prob- lems, Issues, and De c i s i o n s ( Mountain Vi ew, Calif. : Mayfield Publishing, 1996). 22. Faye Harrison, “The Persistent Power of ‘Race’ in the Cultural and Political Economy of Racism,” Annual Review of Anthropology, vol. 24, 1995, pp. 47-74; and Ida Susser and T h o m a s Patterson, eds., Cultural Diversity in the United States: A Critical Reader (Malden, Mass.: Black- well, 2001). K

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Vaidyanathan 2011 Chimpanzee cultures (2).pdf

Thump! Thump! Thump! As the hollow sound echoes through the Liberian rainforest, Vera Leinert and her fellow researchers freeze. Silently, Leinert directs the guide to investigate. Jefferson ‘Bola’ Skinnah, a ranger with the Liberian Forestry Develop- ment Authority, stalks ahead, using the thump- ing to mask the sound of his movement.

In a sunlit opening in the forest, Skinnah spots a large adult chimpanzee hammering something with a big stone. The chimpanzee puts a broken nut into its mouth then contin- ues pounding. When Skinnah tries to move closer, the chimp disappears into the trees. By the time Leinert and her crew get to the clear- ing, the animal is long gone.

For the past year, Leinert has been trek- king through Sapo National Park, Liberia’s first and only protected reserve, to study its chimpanzee population. A student volunteer at the Max Planck Institute for Evolutionary Anthropology (EVA) in Leipzig, Germany, Leinert has never seen her elusive subjects in the flesh but she knows some of them well. There’s an energetic young male with a big belly who hammers nuts so vigorously he has to grab a sapling for support. There are the stronger adults who can split a nut with three blows. And there are the mothers who parade

through the site with their babies. They’ve all been caught by video cameras placed strategi- cally throughout Sapo.

Chimpanzees in the wild are notoriously difficult to study because they flee from humans — with good reason. Bushmeat hunt- ing and human respiratory diseases have deci- mated chimpanzee populations1, while logging and mining have wiped out their habitat. Pop- ulation numbers have plunged — although no one knows by exactly how much because in most countries with great apes, the animals have never been properly surveyed.

The Pan Africa Great Ape Program, the first Africa-wide great-ape census to be mounted, could change that. In addition to surveying chimpanzee numbers (see ‘How many chim- panzees are left?’), project scientists plan to set up automated video and audio recording devices at 40 research sites in 15 countries with chimp populations. Led by Christophe Boesch, director of the primatology depart- ment at the EVA, and Hjalmar Kühl, also at the EVA, the programme aims to get a picture of how chimpanzee behaviour — from nut cracking to vocal calls — varies across Africa. Ultimately, the hope is to learn about the ori- gins and extent of what, in humans, would be called culture.

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In Liberia, camera traps helped researchers to get to know a young chimp, seen here cracking nuts.

Do chimpanzees have traditions? As wild

populations dwindle, researchers are

racing to find out.

The cultured chimpanzees

Until recently, scientists regarded culture — defined as socially transmitted behaviours — as exclusive to humans, but there is growing recognition that many animals exhibit some sort of culture. Chimpanzees, which share 98% of their genes with humans, have the most var- ied set of behaviours documented in the ani- mal world. The difference between humans and animals is growing less distinct, say some researchers. “It is not black and white,” says Kühl, who is Leinert’s supervisor at the EVA.

In the old scenario, “only humans have cul- ture”, says Jason Kamilar, a biogeographer in the department of anthropology at Yale Uni- versity in New Haven, Connecticut. “Then, culture would be the defining feature of humanity, which evolved some time after the split between the human and chimp lineages,” he says. But “if chimps have culture, then pre- sumably the last common ancestor of chimps and humans had culture”.

MAPPING BEHAVIOUR Some chimps dance slowly at the beginning of rain showers, others don’t; some use long sticks to dig up army ants; others use short sticks. In West Africa, some chimp groups hammer nuts with a stone or a piece of wood to open them. But east of the river Nzo-Sassandra, which cuts

across Côte d’Ivoire, only one group has been seen cracking nuts.

So far, researchers have observed these varia- tions over years spent studying groups of chim- panzee that have been carefully habituated to the presence of humans. There are just 12 such colonies in Africa (see ‘Chimpanzee census’),

the most famous of which is in Gombe Stream National Park in Tanzania, where primatologist Jane Goodall worked.

In 1999, evolutionary psychologist Andrew Whiten of the University of St Andrews, UK, and his colleagues compiled a list of behaviours seen in seven of those groups and showed that chimpanzees have unique traditions depend- ing on where they live2. They identified at least 39 behaviours from a list of 65 that varied between groups for no obvious reason.

In humans, culture is passed on from one person to another, and in laboratory stud- ies chimpanzees have shown the capacity to pass on learned customs. In one experiment, Whiten and his colleagues taught two chimps a complex series of steps for getting food from a box. Soon after the chimps were reunited with their groups, all the animals were using this method to get their food3. But whether such social learning happens in the wild is less clear. Gorillas and bonobos can also learn to use tools in the lab, but rarely use them in their natural habitat4.

Deciphering culture in the wild is difficult because researchers must ensure that behav- ioural differences between groups do not have other causes, such as variation in genetics or environmental conditions. “Why is it all chimps don’t do everything? One solution is that there are hidden ecological differences between populations,” says primatologist Richard Wrangham at Harvard University in Cambridge, Massachusetts. A behaviour could be linked to any number of variables such as amount of rainfall, the types of tree available, or the kinds of predator in the area, he says.

These influences can be subtle, as research- ers found while studying how chimps use sticks to harvest army ants. Chimpanzees in

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“THE DIFFERENCE BETWEEN HUMANS AND ANIMALS IS GROWING LESS DISTINCT.”

A female chimpanzee in the Kasakela community in Gombe, Tanzania, shows her offspring how to use a stem as a tool to remove termites from a mound.

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Guinea sometimes use short sticks and some- times use sticks up to twice as long. No reason for this was obvious until Tatyana Humle, an anthropologist at the University of Kent, UK, found that some ants are more aggressive, with longer legs and larger mandibles; they run up sticks quicker and bite harder5. This might explain why chimps elsewhere in Africa also choose tools of varying lengths to get at ants.

But researchers have not been able to find obvious explanations for other variations related to ant harvesting. Chimpanzees in Cote d’Ivoire sweep the ants off their sticks and into their palms before eating; in Guinea, only about 320 kilometres away, the animals stick the ant-laden sticks directly into their mouths. The same type of ant is present in both places.

Ruling out genetic influences is equally com- plicated. This year, molecular ecologist Kevin Langergraber at the EVA and his colleagues compared genetic and behavioural data for nine groups of chimpanzee. They found that communities with greater overlap in their mitochondrial DNA showed more similarities in their behaviour6. “What we are saying is, you haven’t really ruled out the genetic explana- tion,” says Langergraber.

There may be a few hundred thousand chimpanzees in Africa, but researchers have studied just 700–1,000 chimpanzees at the dozen sites with well habituated colonies, says Whiten. The available information from those groups is too little to determine how genes and the environment influence behavioural

variations. Kühl compares the situation to using a handful of villages scattered around the world to draw basic conclusions about all the rituals that define human culture.

Whiten and his colleagues are now carrying out more detailed comparisons of the behav- iour and ecology of chimps at all the habitu- ated sites. But it has taken 50 years to capture the data they are using, most of which were recorded by painstaking observational studies.

The way forward may be the use of cameras hidden in strategic sites, like those Leinert and her team are setting up in Liberia. Such techniques have already proved their worth. Two years ago in Gabon, Boesch and his team were puzzled by random pits they observed in the ground. They set up camera traps and

obtained video recordings of chimps digging to extract honey from underground bees’ nests — something that had never been seen before7.“Camera traps are proving to be an exciting way to reveal new and often complex behavioural techniques in wild chimpanzee communities,” says Whiten.

CAUGHT IN THE ACT At the site in Sapo, Leinert pulls on gloves to measure the rock used by the chimp to crack open nuts of the Guinea plum, Parinari excelsa. The rock is sizeable, weighing in at 880 grams. She collects nuts for later analysis, as well as hair and dung samples for genetic studies.

Leinert may later put up a video camera at the location to collect more data on the

The Pan Africa Great Ape Program is tallying the population of chimpanzees and other apes in 15 countries. As part of the project, researchers are setting up temporary research sites with recording devices to study ape behaviour. These will augment existing knowledge gained from long-term research sites.

CHIMPANZEE CENSUS

Pan troglodytes verus

Chimpanzee subspecies

Pan troglodytes ellioti

Pan troglodytes troglodytes

Pan troglodytes schweinfurthii

Countries of the Pan Africa Great Ape Program

Long-term study sites where chimpanzees are habituated

Temporary research sites

In Gabon, camera traps have helped researchers to discover how chimpanzees collect honey from underground bees’ nests.

Sapo National Park. Preliminary data suggest that Liberia has at least 3,300 chimpanzees.

Chimpanzees on the west side of the Nzo-Sassandra River crack nuts, but that behaviour is almost unknown east of the river.

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Hjalmar Kühl (left, front) and fellow researchers are surveying Liberia’s Sapo National Park to tally chimpanzee numbers. Audio (right) and camera traps in the park record chimp behaviour.

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nut-cracking behaviour. The cameras are mounted in boxes on tree trunks at the height of a chimp’s shoulder, and powered by rechargeable batteries. An infrared motion detector activates the camera for one minute when anything moves in its range.

Near the nut-cracking site, a solar-powered audio device is already continuously recording the forest sounds. Chimpanzees emit a range of calls, including short, high-pitched ‘pant hoots’ that are unique to each individual, and researchers can use them to identify individu- als and to tally the size of a community. These calls may be a form of vocal culture, somewhat like human dialects8.

Over the next five years, the Pan Africa Great Ape Program will establish similar recording stations at locations across Africa. “So potentially we might have, in a few years, behavioural differences from 40 different populations, which is, as you know, four times more than what we have now,” says Boesch.

Kühl proposes that these data could help in designing computer models to test how genes, ecology and social transmission influence the distribution and spread of behaviours such as nut cracking. One idea is that when female chimpanzees reach sexual maturity and move to new communities, they pass along their learned behaviours. Another possibility is that each group invents its own behaviours, some of which catch on and become a culture. Individual practices can die out in particu- lar groups but thrive in others. Or, it might

be that some chimp groups refuse to take up new ways of doing things from incoming individuals. This could explain why some populations show similar behaviours and others do not.

Before Kühl and his colleagues can conduct the modelling work, they need to devise a faster way to go through the recordings made by the camera and audio traps, which are accumulating at a rate of hundreds of hours each month. Students are currently carrying out the analysis but it can take 10 hours to go through an hour of video, according to Kühl. So engineers at the Fraunhofer Institute for Digital Media Technology, based in Ilmenau, Germany, have developed a computer algo- rithm to recognize individual chimpanzees from their facial patterns and distinctive fea- tures, such as the wrinkles under their eyes. In tests of zoo animals, the software can cor- rectly identify individual chimpanzees 83% of the time, and it processes recordings ten times

faster than a person can. Nevertheless, the cam-

eras cannot reveal how an adult chimp patrols its range, or other actions that play out over a wide area. The full portfo- lio of traditions in the community will remain a mystery. And auto- mated recordings will never capture the subtle

ecological information — such as the man- dible size and leg length of army ants — that may eventually explain particular behaviours. These require boots on the ground, and long- term behavioural studies are needed to see how chimpanzees pass traditions on to each other as a driver of culture.

But already, the 30 cameras that Leinert has set up in Sapo Park have delivered some tanta- lizing clues. She is most interested in the lively young male she calls ‘Janosch’, whom she likes for “his big belly and the way he strikes out to crack the nuts”. Besides being entertaining, he sometimes carries his pounding rock away with him, something Leinert hasn’t seen with most other chimpanzees in Sapo. The prac- tice may yet catch on with others there. If so, Leinert could be seeing the beginnings of a cul- tural variation, captured by the cameras she set up in the forest. ■

Gayathri Vaidyanathan is an International Development Research Center fellow at Nature. 1. Köndgen, S. et al. Curr. Biol. 18, 260–264 (2008). 2. Whiten, A. et al. Nature 399, 682–685 (1999). 3. Whiten, A., Horner, V. & de Waal, F. B. M. Nature 437,

737–740 (2005). 4. McGrew, W. C. Science 328, 579–580 (2010). 5. Schöning, C., Humle, T., Möbius, Y. & McGrew, W. C.

J. Hum. Evol. 55, 48–59 (2008). 6. Langergraber, K. E. et al. Proc. R. Soc. B 278,

408–416 (2011). 7. Boesch, C., Head, J. & Robbins, M. M. J. Hum. Evol.

56, 560–569 (2009). 8. Mitani, J. C., Hasegawa, T., Gros-Louis, J., Marler, P. &

Byrne, R. Am. J. Primatol. 27, 233–243 (1992).

Jacob the chimp, now two years old, spends most of his day in a wooden box not much bigger than himself. Born in Sapo National Park in Liberia, he was rescued by a forest ranger, who found Jacob and his dead mother in the arms of a poacher.

Such tales are common in Africa. Bushmeat is a vital source of protein and a dead chimpanzee can fetch US$200 in Nigeria. No one knows exactly how many chimps there are in the wild: in 2003, the International Union for Conservation of Nature made a very rough estimate of 172,700–299,700. But the population is declining rapidly, and many communities are likely to disappear in the next few decades. A study in 2008 found that the population in Côte

d’Ivoire had decreased by 90% in 17 years.

In 2010, the dearth of data prompted the Max Planck Institute for Evolutionary Anthropology (EVA) in Leipzig, Germany, to team up with the Wild Chimpanzee Foundation, headquartered at the EVA, and Conservation International, based in Arlington, Virginia, to launch the Pan Africa Great Ape Program. They aim to conduct nationwide surveys in 15 countries to estimate how many chimps are left in Africa. The scientists involved would not disclose the project’s budget, but acknowledged that the surveys will be expensive and that they do not yet have all the necessary funding.

As part of the survey, graduate student Jessica Junker of the EVA and her Liberian team of graduate

students and rangers from the Forest Development Authority are walking some 400 kilometres to survey 68 squares laid out on a grid across the country. They trek through uncut bush and overgrown farms, across rivers, and into deep muddy valleys to look for chimpanzee nests. Each chimp usually builds a new nest every day, and the researchers can estimate the age of a nest from its state of decomposition. They can then extrapolate to get an idea of the number of animals in an area. Their findings so far suggest that Liberia holds at least 3,300 chimpanzees.

Using similar methods in Sierra Leone, the 2008–10 Tacugama National Chimpanzee Census estimated that more than 5,500 chimpanzees live in that country. This is much higher than a 1981 estimate of 2,500,

probably because the earlier survey used less systematic survey methods.

Christophe Boesch of the EVA, who co-heads the Pan Africa Great Ape Program, says that it will guide conservation efforts to where they can do the most good. But getting precise numbers on the great apes in each country is expensive because of the labour involved, and some conservationists would rather see the money spent on enforcing laws against poaching.

“We don’t need a nationwide survey to tell us we are losing the battle,” says David Greer, who coordinates the African Great Apes Program for the conservation group WWF. “We need to be more assertive, more aggressive with intervention measures, trying to stop the decline.” G.V.

H O W M A N Y C H I M P A N Z E E S A R E L E F T ? Researchers are trekking across 15 nations to find out.

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but must be regarded as an early twig in a bush-like radiation of birds. M

Received 15 February; accepted 21 April 1999.

1. Hou, L., Martin, L. D., Zhou, Z. & Feduccia, A. Early adaptive radiation of birds: evidence from fossils from northeastern China. Science 274, 1164–1167 (1996).

2. Peters, D. S. Ein nahezu vollständiges Skellette eines urtümlichen Vogels aus China. Natur und Museum 126, 298–302 (1996).

3. Hou, L., Zhou, Z., Gu, Y. & Zhang, H. Confuciusornis sanctus, a new Late Jurassic sauriurine bird from China. Chin. Sci. Bull. 40, 1545–1551 (1995).

4. Hou, L., Zhou, Z., Martin, L. D. & Feduccia, A. A beaked bird from the Jurassic of China. Nature 377, 616–618 (1995).

5. Elzanowski, A. & Wellnhofer, P. Cranial morphology of Archaeopteryx: evidence from the seventh skeleton. J. Vert. Paleontol. 16, 81–94 (1996).

6. Reisz, R. R. A diapsid reptile from the Pennsylvanian of Kansas. Special Publ. Nat. Hist. Mus. Univ. Kansas 7, 1–74 (1981).

7. Colbert, E. H. & Russell, D. A. The small Cretaceous dinosaur Dromaeosaurus. Amer. Mus. Novit. 2380, 1–49 (1969).

8. Wellnhofer, P. Das fünfte Skelettexemplar von Archaeopteryx. Palaeontographica A 147, 169–216 (1974).

9. Zhou, Z., Jin, F. & Zhang, J. Preliminary report on a Mesozoic bird from Liaoning, China. Chin. Sci. Bull. 37, 1365–1368 (1992).

10. Zhou, Z. The discovery of Early Cretaceous birds in China. Cour. Forchungsinst. Senckenb. 181, 9–22 (1995).

11. Martin, L. D. & Zhou, Z. Archaeopteryx-like skull in enantiornithine bird. Nature 389, 556 (1997). 12. Sanz, J. L. et al. An Early Cretaceous bird from Spain and its implication for the evolution of avian

flight. Science 276, 1543–1546 (1997). 13. Zhou, Z. & Hou, L. Confuciusornis and the early evolution of birds. Vertebr. PalAsiat 36, 136–146

(1998). 14. Hou, L., Martin, L. D., Zhou, Z. & Feduccia, A. Archaeopteryx to opposite birds—missing link from

the Mesozoic of China. Vertebr. PalAsiat. 37 (in the press). 15. Feduccia, A. The Origin and Evolution of Birds (Yale Univ. Press, New Haven, 1996). 16. Chatterjee, S. The Rise of Birds (John Hopkins University Press, Baltimore, 1997). 17. Martin, L. D. & Miao, D. in Short Papers of the Sixth Symposium on Mesozoic Terrestrial Ecosystems and

Biota 217–219 (China Ocean Press, Beijing, 1995).

Acknowledgements. We thank L. Witmer and S. Chatterjee for critical and helpful comments and reviews, and D. Miao for assistance and suggestions. The Chinese Natural Science Foundation, the National Geographic Society (U.S.) and the Grand Project of the Chinese Academy of Sciences supported fieldwork in Liaoning Province, northeast China. M. Tanner did the drawings and J. Chorn the photographs. D. Miao and J. Chorn critically read the manuscript.

Correspondence and requests for materials should be addressed to L.D.M. (e-mail: ldmartin@falcon. cc.ukans.edu).

Cultures in chimpanzees A. Whiten*, J. Goodall†, W. C. McGrew‡, T. Nishida§, V. Reynoldsk, Y. Sugiyama¶, C. E. G. Tutin#✩, R. W. Wrangham** & C. Boesch††

* Scottish Primate Research Group, School of Psychology, University of St Andrews, St Andrews KY16 9JU, UK † Gombe Stream Research Centre, P.O. Box 185, Kigoma, Tanzania ‡ Department of Zoology and Department of Sociology, Gerontology and Anthropology, Miami University, Oxford, Ohio 45056, USA § Laboratory of Human Evolution Studies, Kyoto University, Kyoto 606-01, Japan k Institute of Biological Anthropology, Oxford University, 58 Banbury Road, Oxford OX2 6QS, UK ¶ Primate Research Institute, Kyoto University, Inuyama 484-8506, Japan # Centre Internationale de Recherche Médicales de Franceville, BP 769 Franceville, Gabon ✩ Department of Biological Sciences, University of Stirling, Stirling FK9 4LA, UK ** Department of Anthropology, Harvard University, Cambridge, Massachussetts 02138, USA †† Max-Planck Institute for Evolutionary Anthropology, Insellstrasse 22, 04301 Leipzig, Germany . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

As an increasing number of field studies of chimpanzees (Pan troglodytes) have achieved long-term status across Africa, differ- ences in the behavioural repertoires described have become apparent that suggest there is significant cultural variation1 –7. Here we present a systematic synthesis of this information from the seven most long-term studies, which together have accumu- lated 151 years of chimpanzee observation. This comprehensive analysis reveals patterns of variation that are far more extensive than have previously been documented for any animal species except humans8– 11. We find that 39 different behaviour patterns, including tool usage, grooming and courtship behaviours, are

customary or habitual in some communities but are absent in others where ecological explanations have been discounted. Among mammalian and avian species, cultural variation has previously been identified only for single behaviour patterns, such as the local dialects of song-birds12,13. The extensive, multiple variations now documented for chimpanzees are thus without parallel. Moreover, the combined repertoire of these behaviour patterns in each chimpanzee community is itself highly distinc- tive, a phenomenon characteristic of human cultures14 but pre- viously unrecognised in non-human species.

Culture is defined in very different ways in different academic disciplines15. At one extreme, some cultural anthropologists insist on linguistic mediation, so that culture is constrained to be a uniquely human phenomenon16. In the biological sciences, a more inclusive definition is accepted, in which the significance of cultural transmission is recognized as one of only two important processes that can generate evolutionary change: inter-generation transmis- sion of behaviour may occur either genetically or through social learning, with processes of variation and selection shaping biologi- cal evolution in the first case and cultural evolution in the second. From this perspective, a cultural behaviour is one that is transmitted repeatedly through social or observational learning to become a population-level characteristic17. By this definition, cultural differ- ences (often known as ‘traditions’ in ethology) are well established phenomena in the animal kingdom and are maintained through a variety of social transmission mechanisms18. Well documented examples include dialects in song-birds12,13, sweet-potato washing by Japanese macaques (Macaca fuscata) at Koshima19, and stone handling by Japanese macaques at Arashiyama20. However, each case refers to variation in only a single behaviour pattern.

Tabulations of population differences amongst chimpanzees have indicated that multiple behavioural variants may exist2–7. However, these tabulations have been based on published reports, which, although they record the presence of behaviours, remain problem- atic in three respects: they are incomplete; they frequently do not clarify the extent to which each behaviour pattern is habitual in the community; and they do not systematically document the absence of behaviour patterns present elsewhere. We therefore adopted a different strategy in our attempt to provide a definitive assessment of what is now known of chimpanzee cultural variation.

Phase 1 of the study established a comprehensive list of candidate cultural variants, which are behaviours suspected by research work- ers to be specific to particular chimpanzee populations. Beginning with a list drawn from literature review by A.W. and C.B., the research directors of the major chimpanzee field projects (Table 1) added and defined unpublished candidate patterns. The patterns were then split and lumped as appropriate. This complex, collabo- rative and iterative process produced a listing of candidate cultural variants that were fully and consensually defined (see Supplemen- tary Information; Table 1 gives abridged descriptions). The scope of this list, differentiating 65 categories of behaviour, represents a unique record of the inventiveness of wild chimpanzees.

In phase 2, the research directors assigned to each of these behaviour categories one of the following six codes, as applicable at their site: (1) customary, for which the behaviour occurs in all or most able-bodied members of at least one age-sex class (such as adult males); (2) habitual, for which the behaviour is not customary but has occurred repeatedly in several individuals, consistent with some degree of social transmission; (3) present, for which the behaviour is neither customary nor habitual but is clearly identified; (4) absent, for which the behaviour has not been recorded and no ecological explanation is apparent; (5) ecological explanation, for which absence is explicable because of a local ecological feature; and (6) unknown, for which the behaviour has not been recorded, but this may be due to inadequacy of relevant observational opportu- nities. These codings were cross-checked and confirmed by senior colleagues at each site. Our results are for the seven chimpanzee

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groups with the most long-term observation record, so the ‘unknown’ code was seldom applicable (Table 1). These studies bring together a total of 151 years of direct observation (range 8–38 years), so our data summarize the enormous increase in our knowledge of chimpanzee behaviour achieved in the latter half of this century.

For any row in Table 1, the profile of codings of particular interest with respect to cultural variation is that in which behaviours are recorded as customary or habitual in some communities, yet absent at others. Three other classes of profile need to be recognized and discriminated from this.

First, seven behaviours proposed as potential cultural variants in

Table 1 Variation in occurrence of behaviour patterns across long-term study sites

Site

Bs Ta Go Ma Mk Kib Bd ...................................................................................................................................................................................................................................................................................................................................................................

A 1 Investigatory probe (probe and sniff) H C C H H + (–) 2 Play start (invite play holding stem in mouth) + H C C C C H 3 Drag branch (drag large branch in display) H C C C C H H 4 Leaf-sponge (leaf mass used as sponge) C C C + e C C 5 Branch-clasp (clasp branch above, groom) H C C C C C C 6 Branch-shake (to attract attention, court) C C C C C H C 7 Buttress-beat (drum on buttress of tree) C C C C C C C

B 8 Nasal probe (clear nasal passage with stick) – – – + – – – 9 Comb (stem used to comb through hair) – – – – – – +

10 Insect-pound (probe used to mash insect) + – – – – – – 11 Resin-pound (extract resin by pounding) + – – e? e? – – 12 Branch-hook (branch used to hook branch) + – – – – – – 13 Perforate (stout stick perforates termite nest) – e – – – e e? 14 Dig (stick used as spade to dig termite nest) + e – – – e e? 15 Brush-stick (probing stick with brush end) – – – – – – – 16 Seat-stick (stick protection from thorns) – – e e? e? e e 17 Stepping-stick (walking on sticks over thorns) – – e e? e? e e 18 Container (object used as container) – – + – – – – 19 Leaf-mop (leaves used to mop up insects) – – + – + e e? 20 Leaf-wipe (food wiped from skull etc.) e? + + – – – – 21 Leaf-brush (leaf used to brush away bees) – – + – – – – 22 Open and probe (perforate, then probe) – – – – – – – 23 Sponge push-pull (stick and sponge tool) + + + + e e –

C 24 Algae-scoop (scoop algae using wand) C e e e e e e 25 Ground-night-nest (night-nests on ground) (–) e? + e? e? e? + 26 Anvil-prop (rock used to level anvil) H e e e e e e

D 27 Food-pound onto wood (smash food) C C C – – e? H 28 Food-pound onto other (such as stone) – H C – – e? – 29 Nut-hammer, wood hammer on wood anvil – C – e e e? e 30 Nut-hammer, wood hammer on stone anvil – C – – – e? e 31 Nut-hammer, stone hammer on wood anvil + C – e e e? e 32 Nut-hammer, stone hammer on stone anvil C C – – – e? e 33 Nut-hammer, other (such as on ground) – H – – – e? e 34 Pestle-pound (mash palm crown with petiole) C – – e? e? e? e? 35 Club (strike forcefully with stick) + H H + – + – 36 Termite-fish using leaf midrib + e – – C e e? 37 Termite-fish using non-leaf materials – e C – C e e? 38 Ant-fish (probe used to extract ants) + – + C C – – 39 Ant-dip-wipe (manually wipe ants off wand) + – C – – – – 40 Ant-dip-single (mouth ants off stick) C C + – – – – 41 Fluid-dip (use of probe to extract fluids) – C C H H H – 42 Bee-probe (disable bees, flick with probe) – C – – + – – 43 Marrow-pick (pick bone marrow out) – C – – – – – 44 Lever open (stick used to enlarge entrance) – H C – – – – 45 Expel/stir (stick expels or stirs insects) – C H H H – – 46 Seat-vegetation (large leaves as seat) + H – – – + – 47 Fly-whisk (leafy stick used to fan flies) – H + – – – H 48 Self-tickle (tickle self using objects) – – H – – – – 49 Aimed-throw (throw object directionally) C C C C – + + 50 Leaf-napkin (leaves used to clean body) – + C + – C C 51 Leaf-dab (leaf dabbed on wound, examined) – + + – – C – 52 Leaf-groom (intense ‘grooming’ of leaves) – – C C C C + 53 Leaf-clip, mouth (rip parts off leaf, with mouth) C C – C C H C 54 Leaf-clip, fingers (rip leaf with fingers) – H – + – H C 55 Leaf-strip (rip leaves off stem, as threat) + – H + – H – 56 Leaf-squash (squash ectoparasite on leaf) – – H ? ? – – 57 Leaf-inspect (inspect ectoparasite on hand) – – + ? ? – C 58 Index-hit (squash ectoparasite on arm) – C + – – – – 59 Hand-clasp (clasp arms overhead, groom) – H – C C C – 60 Knuckle-knock (knock to attract attention) + C H C C – – 61 Branch din (bend, release saplings to warn) – – – – – – – 62 Branch-slap (slap branch, for attention) C C – + – – C 63 Stem pull-through (pull stems noisily) C – + H – H – 64 Shrub-bend (squash stems underfoot) H – – C – – C 65 Rain dance (slow display at start of rain) – H C C C C H

................................................................................................................................................................................................................................................................................................................................................................... A, Patterns absent at no site; B, patterns not achieving habitual frequencies at any site; C, patterns for which any absence can be explained by local ecological factors; D, patterns customary or habitual at some sites yet absent at others, with no ecological explanation. To facilitate comparison, behaviours are listed so that adjacent categories share broad functions; in Band D these are: 27–35, pounding actions; 36–40, fishing; 41–43, probing; 44 and 45, forcing; 46 and 47, comfort behaviour; 48 and 49, miscellaneous exploitation of vegetation properties; 50–57, exploitation of leaf properties; 56–59, grooming; 60–64, attention-getting. Sites (with subspecies, observation period in years by September 1998, site director): Bs, Bossou, Guinea (verus, 23, Y.S.); Ta, Taı̈ Forest, Ivory Coast (verus, 23, C.B.); Go, Gombe, Tanzania (schweinfurthii, 38, J.G.); Ma, Mahale M-group, Tanzania (schweinfurthii, 30, T.N.); Mk, Mahale K-group (schweinfurthii, 18, T.N.); Kib, Kibale Forest, Uganda (schweinfurthii,11, R.W.W.); Bd, Budongo Forest, Uganda (schweinfurthii, 8, V.R.). C, customary; H, habitual; +, present; –, absent; e, absent with ecological explanation; e?, ecological explanation suspected; (–), absent possibly because of inadequate observation; ?, answer uncertain (see text for full definitions). Branch din (behaviour 61) is allocated to band D because it is known to be customary at Lopé, Gabon (C.E.G.T.); behaviours 13,15–17 and 22 are allocated to band B because they have been recorded at shorter-term sites (see Supplementary Information). For full definitions of all behaviours, see Supplementary Information.

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Figure 1 Distribution of behaviour patterns from band D in Table 1 across six

African study sites. Behaviours are arranged in the 5 3 8 arrays to cluster those

behaviours customary or habitual at each site, with clusters for westerly sites on

the left of the array and clusters for easterly sites on the right. The secondary

Mahale site (K) is omitted. Colour icons, customary; circular icons, habitual;

monochrome icons, present; clear, absent; horizontal bar, absent with ecological

explanation; question mark, answer uncertain.

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phase 1 were shown instead to be either customary or habitual in all communities (band A in Table 1). Second, 16 patterns failed to achieve habitual status in any community (band B in Table 1). The third class includes profiles in which all cases of absence are explicable by local conditions (band C in Table 1); just three cases were identified. Absence of algae-fishing can be explained by the rarity of algae, and any absence of ground night-nesting by high predator risk. Use of an additional stone to balance an anvil (anvil-prop) occurs only at Bossou, but it is not expected elsewhere because stone anvils are either not used or (at Taı̈) are embedded in the ground.

The remaining behaviours are absent at some sites but are customary or habitual at others (band D in Table 1). We have found 39 such behavioural variants, significantly more than pre- viously suspected for chimpanzees1–6. We know of no comparable variation in other non-human species, although no systematic study of this kind appears to have been attempted.

We arrive at a similar comparative conclusion when we examine the overall profiles of cultural variants in the different communities (Fig. 1). Some customary and habitual patterns are unique to certain communities, but others are shared between two or more communities (Table 2), so the clusters of variants that characterize each community are not mutually exclusive. Nevertheless, the profiles of each community (Fig. 1) are distinctively different, each with a pattern comprising many behavioural variants. These patterns vary as much between sites associated with the same subspecies (verus at Bossou and Taı̈ in the west, and schweinfurthii at the four eastern sites) as between subspecies themselves. The only major difference between the western and eastern populations is that nut-cracking occurs only in the west, although the fact that this behaviour terminates abruptly at the Sassandra-N’Zo river within the range of the verus subspecies21 shows that it is culturally, rather than genetically, transmitted. The patterns in Fig. 1 can thus be seen to resemble those in human societies, in which differences between cultures are constituted by a multiplicity of variations in technology and social customs14. It remains to be shown whether chimpanzees are unique in this respect, or whether any other animal species, if studied in the same way, would reveal qualitatively similar patterns.

Other comparisons between human and non-human animal cultures have focused on the cognitive processes involved, arguing that if processes of human cultural transmission, such as imitative learning and teaching, are not found in animals, then culture in animals is merely an analogue of that in humans, rather than homologous with it22,23. Our data agree with experimental studies that have shown that chimpanzees copy the methods used by others to manipulate and open artificial ‘fruits’ designed as analogues of wild foods24,25. These experimental designs show differential copy- ing of each of two quite different methods used to process the foods. Similarly, some of the differences between communities described here represent not only the contrast between habitual versus absent, but also the contrast between different versions of an otherwise similar pattern. Examples include cases of tool use, such as the two different methods of ant-dip (Table 1, items 39 and 40); in the first of these, a long wand is held in one hand and a ball of ants is wiped off with the other, whereas in the second method a short stick is held in one hand and used to collect a smaller number of ants, which are transferred directly to the mouth. Other examples occur in social behaviour, such as the variants used to deal with ectoparasites discovered during grooming, with leaf-squash, leaf-inspect and index-hit occurring in different communities (Table 1, items 56– 58). It is difficult to see how such behaviour patterns could be perpetuated by social learning processes simpler than imitation, the most commonly suggested alternative to which is stimulus enhancement26, in which the attention of an observer is merely drawn to a relevant item such as a stick. But this does not mean that imitation is the only mechanism at work. Experimental studies on the acquisition of tool-use and food-processing skills by both children and captive chimpanzees indicate that there is a complex

mix of imitation, other forms of social learning, and individual learning24,25,27–30.

Our results show that chimpanzees, our closest sister-species, have rich behavioural complexity. However, although this study represents the definitive state of knowledge at present, we must expect that more extended study will elaborate on this picture. Every long-term study of wild chimpanzees has identified new behavioural variants. M

Received 24 March; accepted 11 May 1999.

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Supplementary information is available on Nature’s World-Wide Web site (http://www.nature.com) or as paper copy from the London editorial office of Nature. An extended graphical database (unrefereed) of this material is also available (http://chimp.st-and.ac.uk/cultures).

Acknowledgements. We thank T. Matsuzawa, G. Yamakoshi, H. Boesch, D. A. Collins, S. Kamenya, H. Matama, H. Mkono, E. Mpongo, J. Salala, M. Huffman, M. Kasagula, R. Nyundo, S. Uehara, K. Arnold, C. Assersohn, K. Fawcett, J. Kakura, Z. Kiwede, G. Muhumuza, N. Newton-Fisher, P. Pebsworth, E. Stokes, J. Tinka, A. Arcadi, C. Katongole, G. Isabiriye-Basuta, F. Mugurusi, M. Muller and M. Wilson for contributions to the database; D. A. Collins, D. I. Perrett and P. J. B. Slater for advice on the manuscript; and S. Smart for the graphics of Fig. 1.

Correspondence and requests for materials should be addressed to A.W.

Table 2 Number of unique versus shared patterns that are either customary or habitual

Site

Bs Ta Go Ma Mk Kib Bd .............................................................................................................................................................................

Unique 1 8 3 0 1 1 1 Shared 8 16 13 11 9 9 8 ............................................................................................................................................................................. Sites are abbreviated as in Table 1. Unique refers to customary or habitual patterns unique to the sites; shared refers to customary or habitual patterns shared with other sites. Frequen- cies exclude ‘universal’ behaviour patterns identified in band A of Table 1.

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