ANTH essay

THE TRANSITION FROM H. ERECTUS TO ARCHAIC HOMO SAPIENS

In the last lecture we left off with the discussion of Homo erectus and the

adaptive radiation out of Africa.

Remember that Homo erectus was a very long-lived species. It was around for

over 1 million years and in that time it accumulated a great many derived traits.

Derived traits are mutations that arise after a species is separated from the last

common ancestor shared with another species. Essentially, derived traits are “new”

traits. Traits that are carried over from an earlier species, and shared among a number

of species with a shared ancestor are called “primitive” traits.

At about 500,000 BP (years before present) Homo erectus begins to

accumulate enough derived traits that the new population can be classified as a

different species (that, you will remember, is the process called anagenesis). That new

species is generally referred to as Archaic Homo sapiens. Archaic Homo sapiens is a

descriptive term, not a scientific taxonomic name.

Many prefer a more specific scientific name, such as Homo Heidelbergensis. It

could also just be called Homo sapiens sp. (Which means the species Homo sapiens,

without a specified subspecies). But Archaic Homo sapiens will do for our purposes

because we wish to distinguish these early Homo sapiens from later sub-species, such

as Homo sapiens sapiens.

Archaic Homo sapiens (A.h.s.) had a "mosaic" of features. It has some traits

that look like late Homo erectus and some that look like an anatomically modern

human (Homo sapiens sapiens, or AMH to use the convenient acronym). You will

remember that last week, in discussing Homo erectus, I said that the species is very

much like us (Homo sapiens sapiens or Anatomically modern humans, aka AMH) from

the neck down, except that most individuals were more robust. That is, its most

distinguishing characteristics of Homo erectus are in the cranium. It follows that the

most distinguishing characteristics of Archaic Homo Sapiens will also be in the cranium.

Homo erectus is recognized by the flat top of its skull, the prominent brow

ridges, and the almost pentagonal profile of the skull when viewed from the rear.

In contrast, Archaic Homo sapiens has a high and rounded cranial vault like modern

humans. The brow ridges are still there, but are reduced in size, and the front of

the face is a little bit flatter (less prognatic) than Homo erectus. The size of the

brow ridges, the degree of prognathism, and the height of the cranial vault vary by

region and population.

The increasing height of the cranium is due in part to the continued

enlargement of the brain. Although late Homo erectus fell within the range of modern

humans, the average cranial capacity was at the low end of the modern spectrum. At

the same time the brain was growing, the jaw was decreasing in size due to a reduction

in tooth size. The reduction in tooth size was probably due to the larger amount of

cooked food being eaten. Soft food means that there was no selective advantage to big

molars, and so there was a gradual drift downward. With the front of the face getting

smaller, the only place for the brain to go was up. (Motion studies have shown that

enlarging the cranium to the sides or to the back would have created imbalances when

running).

Fossil examples of Late H. erectus/early Archaic Homo sapiens

Germany: Steinheim ~330 kya Similar to Swanscombe with big brow ridges, rounded back

to the skull and 1150 cc.

Africa: The Broken Hill, Zambia skull ~130 kya -cutmarks on the head (“Rhodesian man")

Archaic Homo sapiens Broken Hill, Rhodesia: A mosaic of features

Archaic Homo sapiens in Spain: Atapuerca ~350 kya. Several individuals have been

found in this region. The fossil record from Atapuerca (a region that includes the site of

Sima de los Huesos) is lengthy and, as you might expect, the specimens show a great

deal of variability. Some look erectus-like and some look like later Neandertals in their

features. Asia: Solo, Java, Indonesia ~300-100 kya poorly dated ("Solo man").

Changes in culture

The first Archaic Homo sapiens used material culture derived from the

Acheulean technology. They had handaxes and and chopper tools. Later Archaic

Homo sapiens developed a technology called Middle Stone Age (the term used in

Africa) or Middle Paleolithic (used outside of Africa). Middle Stone Age (MSA)

technology much more specialized than the Acheulean.

Both Acheulean and Oldowan can be described as “core tool” technologies;

together they are called the Lower Paleolithic. In both technologies flakes are

removed from a core, and the core is then the primary tool. In contrast MSA and

Middle Paleolithic technologies are centered on the smaller flakes that are removed

from the core. Moreover, the flakes are worked after removal from the core (through

the

removal of very small flakes or “retouching”). The fine reworking of the flakes shaped

them into a variety of tool shapes. That is, MSA technologies produced specialized

tools, designed with particular tasks in mind. In contrast, both Oldowan and

Acheulean technologies produced more generalized tools.

Archaeological Sites

Clacton-on-Sea, England ~ 300 kya

Menez-Dregan, France ~ 465 kya (thousands of years ago)

Terra Amata, France ~350 kya (beach hut on the ocean) "

Non- utilitarian" behavior Post- mortem (after death) manipulation of human and

animal skulls: Zhoukoudian, China ~ 400 kya

Bodo, Ethiopia ~ 600 kya Ornamentation - ocher.

Tool technology

Europe - Wooden spears shaped like a javelin (for throwing?) at 400,000 ya

Prepared core, or "levallois" tool technology (a core is prepared before the last

blow, which requires imagining it) "Flake" tools (small pieces) and possible composite

tools (e.g. stone "hafted" to wood).

The Neandertals

Homo erectus entered Europe soon after 800, 000 BP. The earliest date comes

from Atapuerca Spain, at 780,000 BP. The European population of Homo erectus did

very well and expanded into northern Europe, England, and Scotland by 500,000 BP.

The pan-genus transition from Homo Erectus to Archaic Homo sapiens suggest that the

European H. erectus maintained contact with the rest of the species and that there

was gene flow throughout H. erectus and early H. Sapiens populations.

Soon after 300,000 years ago (after the development of Archaic H. Sapiens)

the climate began to cool. Glaciers moved southward throughout Europe and Asia.

In Europe the glaciers expanded over the Alps and the Pyrenees ranges, isolated

the European H. Erectus population. That population had to survive in western

Europe during a glacial maximum.

The Neandertals were the product of the western European Archaic H.

Sapiens population adapting to glacial conditions. The “Classic” Neandertals date form

about 150, 000 BP to 25,000 BP. Many of their physical traits are best understood as

cold weather adaptations. Neandertals were short and stocky compared to Archaic H.

Sapiens, and to us. This is an example of Bergman’s rule: stocky bodies preserve heat

better, because they maximize body mass while minimizing suface area. In effect, short

stocky bodies preserve body heat better. Their limb proportions are an example of

Allen’s Rule: in cold climates, the length of body appendages is minimized. In effect,

Neandertals demonstrate a combination of Bergman’s Rule and Allen’s Rule. Their

body cores (chest and torso) are larger than Archaic H. Sapiens, while their arms and

legs are shorter. The Neandertals had large noses and sinuses, which functioned to

warm air before it entered the lungs. These features enlarged their faces and made

them more prognathic (forward projecting) than Archaic Homo sapiens.

To counterbalance the forward-projecting face, the Neandertals developed an

occipital bun (a bony mass on the back of the skull). Motion studies by David

Lieberman at Harvard have shown that the counterbalance of the occiptal bun served

to

kept the head steady while running. In this way, Neandertals were able to maintain

a steady focus on prey as they ran.

The cranial capacity of Neandertals was actually larger (1300 -1640 cc) than

that of modern humans (ca 1300 cc on average). Because of their larger body mass,

however, the Neandertal ratio of mass to brain capacity is equal to that of modern

humans.

Neandertal fossils

La Chapelle aux Saints, France

Neandertal, La Ferrasie, France

Neandertal:

Skhul V, Israel 35 kya

Cultural behaviors

The stone tool industry most closely associated with Neandertals is called the

Mousterian. Mousterian is effectively a Middle Stone Age technology, based upon the

specialized working of flakes.

One distinctive product of the Mousterian technology is the “Levallois flake.”

A Levallois flake is one removed from a carefully prepared core. The final product is

removed from the core with a single blow and yields a beautifully shaped tool with

sharp edges around is margins.

Other Neandertal cultural characteristics

Neandertals buried their dead. Neandertal fossils have been found in

prepared pits, or graves. Neandertals Cared for the old and sick. Many Neandertal

fossils show severe injuries, such as amputations, that would have made it

impossible for

them to fend for themselves. Those individuals were nursed back to health and were cared

for afterwards. Many Neandertal skeletons show severe injuries that include broken bones.

The best modern analogues to those injuries come from rodeo riders. The suggestion has

been made that Neandertals attacked their prey “up close and personal.” That is, they may

have jumped on their prey and dispatched them with knives, rather than using spears, darts,

or traps.

Dental wear patterns (cutmarks visible under the microscope) show they

probably held food with their teeth and then cut it off. They display taurodontism, or

an enlarged pulp cavity in the molar.

Neandertal classification problems

Some physical anthropologists (e.g. Ian Tattersal and Tim White) believe that

the differences between Neandertals and Archaic Homo sapiens is so great that they

should be given a separate species designation (Homo neandertalensis). Others feel

that they are just a distinctive population of Archaic Homo sapiens (Homo sapiens

neandertalensis). Genetic studies (see below) suggest that Nendertals were capable

of interbreeding with H. Sapiens sapiens and producing fertile offspring; hence, they

belong to the same species.

After 90,000 BP the glacial ice of Europe began to retreat and the Neandertals

spread into Eastern Europe and southwest Asia (the Near East: Lebanon, Syria, Israel,

Palestine).

They lived there for tens of thousands of years, although they were highly mobile

and did not reside in one place for long. At the same time, however, another group

of hominids was moving northward out of Africa. This latter group was Homo sapiens

sapiens, who are known colloquially as Anatomically Modern Humans (AMH).

Homo Sapiens Sapiens

For the sake of brevity, I’ll use the term Anatomically Modern Humans (AMH) to refer to H.

Sapiens sapiens.

While the Neandertals were developing in western Europe, archaic Homo sapiens were

having fun elsewhere. The archaeological record of Archaic Homo sapiens is weak in Asia

outside of cave sites, such as Zhoukoudian in China. So with the exception of that single (but

spectacular site) there is not much to go on. In Africa,

however, the record of Archaic Homo sapiens and the Middle Stone Age is very, very

good.

The Powerpoint presentation includes a map of some of the best-known archaeological

sites of the MSA (Middle Stone Age). In recent years, the record has included some finds of

“modern” behavior that twenty years ago was thought to be no older than about 20,000

years. These behaviors include the creation of art and personal adornments such as jewelry.

Despite increasing cultural complexity, Archaic H. Sapiens faced a crisis of sorts just

before 200,000 years ago. Environmental degradation reduced human populations to very

low levels, perhaps no more than a few thousand people. Out of this crisis, a new population

developed and they are labelled Homo sapien sapiens, or AMH.

Physical Characteristics of AMH

Some of the distinguishing traits of AMH are continuations of trends begun with

Archaic H. Sapiens. These included a higher cranial vault, flatter face, and smaller teeth.

One unique trait of AMH however, is the presence of a notable chin. All archaic H.

Sapiens (including Neandertals) have a receding chin, whereas all AMH (except perhaps

the British royal family) have chins.

Distinctive cultural behaviors of AMH

The distinctiveness of AMH behavior has been undermined by the recent

discovery of “modern” behaviors during the Middle Stone Age (MSA). There are,

however, trends in behavior that quicken after the appearance of AMH. These

behaviors include1) the use of “Upper Paleolithic” technologies including blades

(stone tools with parallel edges), harpoons, and objects made from bone and

antler. 2) Symbolic behavior, including “art”

and personal adornment (beads and other jewelry) Some have suggested, also, that marks

on stones and bone represent a type of notational system, perhaps for counting or even a

calendar.

The use of blades, barbed points (such as harpoons), and the increasing use of bone

are customarily used to define the “Upper Paleolithic.” It is best to think of Upper Paleolithic

as a type of technology, rather than a time period. The reason for that is simply that while

AMH are using their Upper Paleolithic technology, Neandertals are using the Mousterian (a

Middle Paleolithic technology). So, one group is using Middle Paleolithic technology while

the other is using Upper Paleolithic technology. If that is confusing to you, things will get

much worse in just a minute

The Fossil Record of Homo sapiens sapiens

Anatomically modern humans (homo sapiens sapiens) first appear in the fossil record

soon around 200,000 BP. A set of skulls from the site of Herto, Ethiopia dated to about

160,000 BP have undeniably modern traits, including a flat face and a high cranial vault. Soon

after, AMH fossils from Klasies River Mouth and Border Cave (150,000 - 120, 000 BP) have

similar traits. After 100,000 BP the fossil record becomes much larger.

Genetic Evidence for Homo sapiens sapiens

Recent advances in genetic studies have significantly altered how we understand

early AMH. The first genetic study done in 1998 by Rebecca Cann, Mark Stoneking and Alan

Wilson of UC Berkeley suggested that modern humans developed out of a population that

lived in Africa between 150,000 and 200,000 years ago. This study used mitochondrial DNA, a

type of DNA that occurs outside the nucleus of cells (Mitochondria help to produce energy

for cells). Unlike nuclear DNA, which come from both mother and father, Mitochrondrial DNA

(MtDNA) are passed only through the mother. Thus MtDNA is much easier to analyze than

nuclear DNA. Cann, Stoneking, and Wilson collected MtDNA from living people with ancestry

in different parts of the world. They used a type of statistical cluster analysis to determine

how closely related modern people are to one another. Using a known event to determine a

mutation rate, they calculated that all living people last shared a common female ancestor

just over 150,000 years ago and that the common ancestor lived in Africa.

The popular accounts in the press labeled the hypothetical ancestor as the "African

Eve" and their theory of a recent common ancestor became known as the "Eve Hypothesis."

In point of fact, what Cann, Stoneking, and Wilson claimed was all living peoples are

descended from a small population (not necessarily a single woman) that lived in Africa prior

to 150,000 years ago. Although there were some problems with their statistics and their

methodology (they sampled African-Americans as proxies for African populations, rather than

modern Africans), held up for many years.

A very important study published in 2018 suggests that the history of early AMH

was much more complex. A team led by Eleanor Scerri proposed that early AMH populations

emerged from diverse and numerous populations within Africa. Chris Stringer, a co-author with Scerri said

“"When we look at the morphology of human bones over the last 300,000 years, we see a complex mix of

archaic and modern features in different places and at different times… As with the material culture, we do

see a continental-wide trend towards the modern human form, but different modern features appear in

different places at different times, and some archaic features are present until remarkably recently."

If you have time, you can read about the Scerri study at

https://www.sciencedaily.com/releases/2018/07/180711114544.htm

The Multi-Regional Hypothesis

The Multi-Regional Hypothesis has been most forcefully advocated by Milford Wolpoff, of the

University of Michigan (now retired). Wolpoff believes that AMH developed in various regions

throughout the world from populations that go back to the adaptive radiation of Homo erectus.

That is, according to Wolpoff, modern Asians descend from Asian Homo erectus, Modern Africans

descend from African Homo erectus, modern Europeans descend from European Homo erectus,

etc. In this model, there was gene flow between those regional populations that spread derived

traits throughout the world populations of the genus Homo, effectively keeping everyone

moving along the same line of development.

Wolfpoff believes that he can trace certain biological traits from Homo erectus

populations up to modern times in each region. For example, modern Asian populations

(and Native Americans) have a distinctive shape to their incisor teeth, called "shovel- shaped

incisors". There is a thick rim of enamel on the edge of the teeth that give them the

appearance of a flat-end shovel. Wolfpoff identifies that trait in Asian Homo erectus (the

Zhoukoudian specimens) and believes he can trace it all through the fossil records, up to

modern Asians.

Few physical anthropologists agree unreservedly with Wolpoff. First, many of the

derived traits he identfies in the regional Homo erectus populations are week.

Personally, I don't see shovel-shaped incisors in the Zhoukoudian specimens. Second, the

fossil record in Asia is almost nonexistant at 100,000 BP, so demonstrating cultural

continuity is almost impossible.

Another problem is whether we are looking at homologous traits or analogous traits.

Here, occipital buns are a good example. Neandertals had occipital buns. Many

western Europeans today also have occipital buns. (In the interest of full disclosure, you

should know that I have an occiptal bun). But not all buns are the same. As I mentioned,

Daniel Lieberman at Harvard studied Neandertal crania and found that in that species the

occipital bun developed to counterbalance a prognathic face. What Lieberman found in

modern humans, however, is that the occipital bun is the product of an expanding brain.

Modern humans with an occipital bun also have skulls that are narrow in front (above the

eyes). That is, modern humans have an occipital bun because their skulls are constricted in

front: the skull expanded to the back in order to hold the increasing size of the brain. In short,

Lieberman says that occipital buns in modern Europeans have nothing at all to do with

Neandertals and are not evidence of genetic continuity.

Wolpoff’s ideas cannot be accepted without many qualifications, and it is largely

incompatible with the genetic and fossil evidence that AMH originated in Africa.

However, the evidence that AMH interbred with the Neandertals and perhaps other populations

such as the Denosivans, keeps some of Wolpoff’s ideas in play.

The Denosivans

The Denosivans were a population of Archaic Homo sapiens known only from a small

number of fossils. The population was defined by the genetic analysis of a finger bone and a

tooth from Denosiva Cave, in southern Siberia. According to Svaante Pääbo of the Max

Planck Institute, whose laboratory conducted the analysis, the study of the Denosiva fossils

represents the first time that a new hominin population was defined on the basis of genetic

analysis, rather than on the basis of fossil traits.

Analysis of the mitochondrial DNA shows that the specimens classified as “Denisovan” were

genetically distinct from Neandertals and modern humans. Analysis of nuclear DNA suggests that

Denisovans shared a common origin with Neandertals, separating at some point after 1 mya. Later,

Denisovans ranged from Siberia to Southeast Asia, interbreeding with both

Neandertals and AMH. The Denosivan genetic analysis supports the hypothesis that

Neandertals and Denisovans were more closely related to one another than either was to

modern humans. However, all three populations were capable of interbreeding with

one another.

In 2013, mitochondrial DNA from a 400,000-year-old femur from Atapuerca, Spain,

which had been though to be either Neandertal or Archaic homo sapiens, was found to be closer to

Denisovan mtDNA than to Neandertal mtDNA. This finding suggests that Denisovans ranged widely in

Eurasia before being incorporated into other populations.

A very recent study, published in August, 2018 announced that one bone from Denisova cave

represented a woman whose father was genetically Denisovan and whose mother was Neandertal. That

specimen, called Denisova 11 had chromosones that we half Neanderthal and half Denosivisan. Carl Zimmer,

a science writer with the NY Times summarized the study:

“An examination of the X chromosome showed that Denisova 11 was female. As for

which parent was which, the mitochondrial DNA held the answer: Since these genes

are only passed down from mothers, Denisova 11’s mother was Neanderthal. Her

Denisovan father’s kin were local, it turned out. His DNA most closely resembles the

genetic material from Denisova 3’s pinky, discovered at the cave in 2010. She lived in

the cave a few thousand years after Denisova 11, the hybrid human. Her

Neanderthal mother, however, was closely related to Neanderthals who lived

thousands of miles to the west in what is now Croatia, 20,000 years after Denisova

11 died. She was only distantly related to the Neanderthals who lived in the cave

120,000 years ago.”

Zimmer’s report on this new study is at:

https://www.nytimes.com/2018/08/22/science/neanderthals-denisovans-

hybrid.html

Perhaps most importantly, the genetic evidence shows that the genome of the

Denisovan populations survives in modern human populations. The modern indigenous

peoples of Australia and New Guinea may derive up to 6% of their genome from the

population to which the Denisovan fossils belonged. The populations of Melanesian and

Polynesia also contain Denisovan DNA. However, other Asian populations do not

contain Denisovan DNA.

The Denisovans remain enigmatic because of the small number (n=11) and fragmented nature of

the fossils attributed to the species (teeth and fingers). Nonetheless, the identification of the Denisovan

population serves as another reminder of the complex history of human populations in the Middle and

Upper Paleolithic periods. The story is not one of a single line ‘progressing’ from Homo erectus to Homo

sapiens sapiens. There were many, many populations of humans, some of which developed enough

mutations to be classified as distinct species or sub-species. Some of those many populations interbred

with one another. Some of those populations went extinct, while some survived.

What happened to the Neandertals?

The last Neandertal disappeared by about 25,000 BP, if not earlier. That is, after 25,000

years ago we don't see any fossils with Neandertal traits. What happened to

them?

Here are the three logical alternatives:

1) Neandertals were pushed to exinction by AMH and there was no significant contact

between the two groups.

2) Neandertals interbred with AMH, so that some of their genome survives today.

3) Neandertals intebred with AMH, but their genome does not survived today either

because they were "genetically swamped" by a larger AMH population or because

the offspring were not fertile. The latter outcome would be because they were so

genetically distinct that even if they had mated, any offspring could not reproduce (in

effect, Neandertals and AMH were separate species).

The Neandertal case is the principal data set available to us for testing the alternative

hypotheses for how early AMH interacted with other hominin populations. There are actually

two data sets available. First is the archaeological and the second is genetic.

Archaeology

Neandertals and AMH encountered one another in two settings: Europe and the Near

East. Neandertals expanded into the Near East after 90,000 BP. We know from a very recent

study in Israel that AMH were in the Levant by 100,000 BP. But it wasn't until about 40,000

years BP that AMH expanded beyond the Near East. We can trace that expansion because

the

Upper Paleotlithic tool kits used by AMH moves northward and westward. At the same time,

the distribution of Mousterian tool kits used by Neandertals becomes more restricted.

Seemingly, AMH is pushing the Neandertals back into western Europe. It could be, however,

that Neandertals are adopting Upper Paleolithic technologies and that the two populations

were interbreeding.

In short, the archaeological evidence is inconclusive and the data are hotly debated.

Some archaeologist propose that at about 50,000 BP the Neandertals of western Europe

developed a new type of stone tool technology, called the Chatelperronian that was quite

sophisticated. They see continuity in that tool technology up to ca. 15,000 BP, well after the

Neandertals ceased to exist as a biological population. Other archaeologists, however, argue

that Chatelperronian was invented by AMH as they reached western Europe. Those

debates will not be resolved any time soon, and perhaps are not resolvable.

The Biological and Genetic Data

Svante Pääbo, a scientist at the Max Planck Institute, in Munich, Germany pioneered

the analysis of Neandetal DNA. He and colleagues working at the Max Planck Institute have

revolutionized our understanding of human origins.

Initially, Pääbo was able to collect 0.4 grams of a sample from the upper arm bone of a

skeleton found in 1857. In a 1997 study, Pääbo compared 378 base pairs of the Neandertal's

mitochondrial DNA to that of modern humans. He found that there were an average of 27

differences between modern and Neandertal DNA. For comparison, the typical variation

among modern humans is just 8 differences. Some interpreted the results to mean that

Neandertals are so vastly different from modern humans that they must be a different

species. Others said the results demonstrated that Neandertals contributed nothing to the

modern human genome. Both interpretations proved to be wrong.

In a second study, published in 2010, Pääbo and his team analyzed nuclear DNA

extracted from Neandertal fossils and compared it to modern human DNA

sequences.

They found a correspondence of 1% to 4% between Neandertals and non-African modern

humans. Pääbo and his colleagues deduced from this result that interbreeding between

Neandertals and AMH did occur, and that it took placed outside of Africa, after the AMH

diaspora of about 100,000 years ago but before AMH spread into Asia. They deduced that

the Levant is the most likely place where such inter-breeding took place, and the estimate

a date of approximately 100,000 – 60,000 years ago for the contact.

More recent studies have expanded upon the 2010 findings. New ‘hot spots’ for

interbreeding between Neandertals and AMH have been identified within Europe,

especially in northern Italy. The first complete sequence of a Neandertal nuclear genome

was published in 2014 (Prufer et al 2014). That sequence came from a fossil from the Altai

Mountains in Siberia. The individual was female and it is likely that her parents were half

siblings. There was other evidence of such pairings earlier in her ancestry, which may again

reflect that Neandertal populations were small. The analysis also showed that this

individual was closely related to both modern humans and the Denisovans.

New DNA studies show that Neandertals have contributed approximately 1-4% of the genomes

of non-African modern humans. However, Fu et al. (2015) found that an anatomically modern

human who lived about 40,000 years ago had approximately 6-9% Neandertal DNA. Those data are

consistent with the idea that Neandertal populations were smaller than those of AMH.

In 2016 a suite of studies extracted DNA from Neandertal fossils from Altai Cave in Siberia, as

well as from Spain and Croatia. These studies estimate that interbreeding of Neandertals and AMH

took place around 100,000 years ago (Kuhlwilm et al 2016). Importantly, those studies were the first

to show AMH gene flow into the Neandertal genome, as opposed to Neandertal DNA into the AMH

genome. These data suggest that Neandertal/AMH interbreeding was more frequent than previously

thought and that migrations of AMH out of Africa took place earlier than thought. That latter

prediction was proven in 2018 with the discovery of AMH fossils dating to around 200,000 BP.

The hypothesis that Neandertals simply went extinct, with no interbreeding with AMH has

been thoroughly refuted. All AMH populations outside of Africa have some Neandertal DNA.

In summary, the genetic data show that AMH met and interbed with multiple

Neandertal populations across wide distances and at various points in time. These new

data, combined with the analysis of the Denosivan fossils, emphasize that we cannot think

about linear succession of hominin species (e.g., Homo habilis gives rise to Homo erectus

which gives rise to Homo sapiens, etc), but must think about different populations of

hominins interacting with one another in complex ways.

Fossil Evidence for AMH/Neandertal Contact

Fossil evidence may also support the scenario for interbreeding between

Neandertals and AMH within Europe. The fossil remains of a child from Lagar Velho, have

been interpreted by Joao Zilhao and Erik Trinkaus to show evidence of hybridization

between Neandertals and AMH. Lagar Velho is a rock-shelter in the Lapedo valley, located

about 140 km north of Lisbon, Portugal. The fossilized remains were found in deposits

dated by radiocarbon to about 25,000 years ago.

Although the Lagar Velho remains are classified as Homo sapiens sapiens (AMH),

the child shows some Neandertal traits in its skull, and also in the proportions of its

lower limbs.

Trinkaus believes that if more quantitative analyses of the fossil record were done,

as it was with the Lagar Velho fossil, scholars would find much more evidence of

Neandertal traits surviving in AMH after 25,000 years ago.

Conclusion

The genetic data, in tandem with new fossil evidence and archaeological analyses

show that although Neandertals, and other populations such as the Denosivans, ceased

to exist as distinctive populations by 25,000 years ago, some of their genome survives

today. Thus, the truth seems to be much more complex than either the “Out of Africa” or

the “Multi-regonal” hypotheses would suggest. It seems certain that Homo sapiens

sapiens (AMH) encountered other hominin populations (especially Neandertals) as they

migrated out of Africa. In many cases, it seems that interaction and interbreeding took

place.

However, it is unlikely that all interactions were the same. This is a very exciting time to be

studying modern human origins and their interactions with other groups.

Addendum: Homo floresensis

Homo floresensis is the name given to a fossil population of hominins from the island of

Flores, which is part of Indonesia, just east of Java. Fossils of the species date from about 60000 BP

to perhaps 90000 BP. Anatomically modern humans arrived on the island about 50000 BP and may

have been responsible for the extinction of H. floresensis.

Homo floresensis is nicknamed “The Hobbit” because of its small size. One male has a

reconstructed height of about 1.1 M (just over 3 ft.).

Small size is often an adaptation to an island environment, where resources are

limited. The ancestry of H. floresensis, however, is debated. Some believe it derives from a Homo

erectus population. (Remember that Homo erectus was first identified in Java by Eugene Dubois

in 1896). This position finds support in the overall similarity of H. floresensis, to H. erectus,

despite the differences in size. An alternative perspective, based on the statistical analysis of limb

proportions, holds that H. floresensis more closely resembles early Homo species, such as H.

habilis. Such a derivation, would require us to hypothesize that there was a radiation out of Africa

prior to the emergence of H. erectus.

For our purposes, we don’t need to be concerned with the origins of Homo floresensis.

It is enough to recognize that it is another example of how a linear model of human evolution is

insufficient to account for the fossil and genetic evidence.