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Humans' head start: New views of brain evolution Gibbons, Ann . Science ; Washington  Vol. 296, Iss. 5569,  (May 3, 2002): 835-7.

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ABSTRACT About 1200 researchers recently converged for the 71st annual meeting of the American Association of Physical

Anthropologists, where brain evolution was one of the hottest topics. Reports on the diet needed to support an

expanding brain and a new tool's view of how the human brain took shape in evolution were discussed.

FULL TEXT Headnote

MEETING

Headnote

BUFFALO, NEW YORK-About 1200 researchers converged here for the 71 st annual meeting of the American

Association of Physical Anthropologists (10 to 14 April), where brain evolution was one of the hottest topics,

including reports on the diet needed to support an expanding brain and a new tool's view of how the human brain

took shape in evolution.

Something Fishy About Brain Evolution

Illustrations of human ancestors routinely show brawny hunters bringing home the wildebeest, butchering meat

with stone tools, and scavenging carcasses on the savanna. But a more accurate image might be ancient

fishermen-and fisherwomen-- wading into placid lakes and quietly combing shorelines for fish, seabirds' eggs,

mollusks, and other marine food.

At a symposium on nutritional constraints on brain evolution, an unusual mix of anthropologists, neurochemists,

nutritionists, and archaeologists debated the kind of diet that must have supported humans' dramatic brain

expansion, focusing on how our ancestors consumed enough of the omega fatty acids essential for brain

development. Although a few researchers suggested that the source was brain and other organ meat, most agreed

that our ancestors must have relied on fish or shellfish. "A shore-based diet was essential for the evolution of

human brains," says nutritional scientist Stephen C. Cunnane of the University of Toronto.

That's because humans, intelligent though we may be, are literally fatheads: About 60% of the brain's structural

material is lipids, almost all of it in the form of two long-chain polyunsaturated fatty acids, docosahexaenoic acid

(DHA) and arachidonic acid (AA), respectively known as omega-3 and omega-6 fatty acids. So when a fetus's brain

is developing, a lack of DHA or AA is "catastrophic," says Cunnane.

These acids are vital to brain growth and function after birth, too. Infant humans and other mammals that lack

these fatty acids show reduced cognitive ability and vision problems. (The retina has the highest concentration of

DHA.) In adults, new data suggest that depletion of these acids may be linked to attention deficit disorders,

dyslexia, senile dementia, schizophrenia, and other problems, according to a review by geochemist C. Leigh

Broadhurst of the US. Department of Agriculture's Environmental Chemistry Laboratory and Michael Crawford of

the University of North London in the April issue of Comparative Biochemistry and Physiology Part B.

People must consume DHA and AA in their diets, because the body cannot synthesize these molecules fast

enough from other fatty acids found in vegetables, nuts, flaxseed, and other sources. Although by far the best

source of DHA is shellfish and fish, particularly cold-water fish such as bluefish and herring, these acids are also

found in brain meat and in the liver of some animals, says physiologist Loren Cordain of Colorado State University

in Fort Collins.

But our ancestors couldn't support an expanding brain by eating brain alone: Crawford calculated that a 350-gram

brain from a 1-ton rhinoceros would barely feed a party of hunters, much less those who needed it most: pregnant

and nursing women and children. To have a reliable source of DHA, particularly to increase brain size rather than

sustain it, Broadhurst says, "many generations of women had access to fish." She adds that many archaeological

sites are by lakes and rivers, so our ancestors must have taken advantage of these obvious resources.

The hypothesis makes sense, says neurochemist Norman Salem Jr. of the National Institute on Alcohol Abuse and

Alcoholism. "I would expect that those early brains as they expanded maintained the high DHA content we have

today," Salem says. "It seems reasonable to me that they evolved around water with marine sources available."

Indeed, for at least the past 100,000 years, the archaeological record of modem humans includes hundreds of

middens-- piles of shellfish shells and fishbone-and other signs of fishing. By 70,000 years ago at Blombos Cave in

South Africa, and perhaps as early as 90,000 years ago at Katanda, Zaire, people carved bone points for fishing,

says anthropologist Alison Brooks of George Washington University in Washington, D.C.

But the brain underwent explosive growth long before this time, probably beginning about 2 million years ago in

hominids who lived in Africa and Asia. Methods to reconstruct their diet by studying the ratios of isotopes of

carbon and strontium in their teeth or bone have so far failed to discern whether they ate marine foods, says Julia

Lee-Thorpe of the University of Cape Town in South Africa. And although some new methods measuring barium

ratios hold promise, it might be difficult to fmd the right hominid remains to test: "For the past 2 million years, the

ocean was 10 meters lower than today," notes geologist Henry Schwarcz of McMaster University in Hamilton,

Ontario. "Where were the fisheating populations living? On the nowsubmerged coast." Many hominids did live near

Africa's abundant lakes, however, and their bones may eventually prove whether or not fish gave our ancestors

food for thought.

Hot Spots of Brain Evolution

Humans may pride themselves on their big brains, but just which parts of the brain expanded during evolution has

been fiercely debated. Now it seems that, compared with chimpanzees, humans may be literally more right-

minded. A powerful new imaging technique presented at the meeting revealed bulges on the right-hand surface of

human brains that are not seen in chimpanzees, suggesting that these areas expanded during our evolutionary

history, perhaps to aid in processing the rhythms and tone of speech.

"The surprise is the degree to which the right side expanded," says speaker Dean Falk,f an anthropologist at Florida

State University, Tallahassee. "It's generally been thought that the left hemisphere was most important because it

is known to be the language-bearing side of the brain. That's true, but we see more changes on the right."

Although the findings are preliminary, the new method, which uses magnetic resonance imaging (MRI) to study

and compare the brains of living people and chimpanzees as well as ancient skulls, is already winning rave

reviews. "I was totally blown away by the technique," says Patrick Gannon, a comparative neurobiologist at Mount

Sinai School of Medicine in New York City.

The technical wizardry that impressed the audience was developed as part of an international effort to map the

activity of living people's brains with functional MRI, which tracks oxygen use by tissues, says developer Karl Zilles,

head of research groups at the Vogt Institute for Brain Research and at the Research Center Julich, both in

Disseldorf, Germany. To compare scans of different people with different imaging methods, Zilles's team recently

developed software that can shrink or blow up brain maps to a standard size without scaling problems.

Zilles realized that he could adapt the method to compare the sides of the brain, and even the brains of different

species-specifically, people, chimpanzees, and extinct hominids. So Zilles and Falk used MRI to make highly

accurate "virtual endocasts"-threedimensional computer images of the right and left sides of human brains. Using

the software to compare the two sides, they found two well-known asymmetries that cause bulges at the surface

of the frontal lobe behind the right eye and the left occipital lobe at the back of the brain. But they also found new

asymmetries, including many areas of the right brain that were larger than the left, such as a semicircle of

expansion from just behind the eye socket to the back of the brain.

Next, they looked at how these areas changed during human evolution. They made virtual endocasts of 10 human

brains. Then, because they couldn't use MRI on live chimpanzees, they submerged skull endocasts from seven

bonobo chimpanzees in water and used MRI to image the water inside the braincase, revealing the shape of the

brain. Next they took the "average" cast of each species and used the software to "warp" and overlay the chimp

endocast on the human one, showing the areas of difference. They also overlaid a scaled functional human brain

map to show the functions of these regions. For example, they discovered a spot behind the right temple (see

illustration; shown in blue), thought to be used to analyze sound, that is smaller in humans than in bonobos.

All in all the team found five hotspots where the shape of the human brain differed from that of chimps, and three

were more dramatic on the right side. Falk then compared the human and chimp casts with those of 13 hominid

skull casts in her collection, ranging from a 2.5million-year-old australopithecine to more recent archaic Homo

sapiens and Neandertals. She found marked changes beginning in australopithecines, whose frontal lobes began

to expand above the nose. But this and other areas, such as the bottom of the lobe behind the temples, expanded

even more in archaic H. sapiens and Neandertals. In fact, notes Falk, the newly located asymmetries between the

left and right brain "are the exact areas that change dramatically in fossils."

The next step is to figure out what functions are carried out by the expanded brain areas-and whether they reflect

deeper underlying structural changes rather than just rearrangements of the tissue next to the skull, says Daniel

Buxhoeveden, a biological anthropologist at the Medical College of Georgia in Augusta.

Falk thinks, for example, that the expansion of the semicircle on the right side may be important for understanding

the prosodic features of speech, such as rhythm, tone, and emotional content. "It was surprising because most

people, including me, are fixed on the idea that speech is dominant on the left side," says Zilles. "Speech is

something human, but many changes are on the right."

-ANN GIBBONS DETAILS

Subject: Brain; Evolution; Conferences; Anthropology

MeSH: Animal, Anthropology, Physical, Brain -- anatomy &histology, Brain -- growth

&development, Brain Mapping, Diet, Dietary Fats, Evolution, Fatty Acids, Unsaturated

-- administration &dosage, Fatty Acids, Unsaturated -- physiology, Fishes, Hominidae

-- anatomy &histology, Human, Magnetic Resonance Imaging, Pan troglodytes --

anatomy &histology, Shellfish

Substance: Dietary Fats; Fatty Acids, Unsaturated

Company / organization: Name: American Association of Physical Anthropologists; NAICS: 813920

Publication title: Science; Washington

Volume: 296

Issue: 5569

Pages: 835-7

LINKS Check for full text in other resources

Number of pages: 2

Publication year: 2002

Publication date: May 3, 2002

Publisher: The American Association for the Advancement of Science

Place of publication: Washington

Country of publication: United States, Washington

Publication subject: Sciences: Comprehensive Works, Technology: Comprehensive Works

ISSN: 00368075

CODEN: SCIEAS

Source type: Scholarly Journals

Language of publication: English

Document type: News

Accession number: 11988554

ProQuest document ID: 213589776

Document URL: https://search.proquest.com/docview/213589776?accountid=8289

Copyright: Copyright American Association for the Advancement of Science May 3, 2002

Last updated: 2017-10-31

Database: SciTech Premium Collection,ProQuest Central

Bibliography Citation style: APA 6th - American Psychological Association, 6th Edition

Gibbons, A. (2002). Humans' head start: New views of brain evolution. Science, 296(5569), 835-7. Retrieved from

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