Download Modern Homo sapiens

Modern Homo sapiens
The first modern Homo sapiens evolved in Africa between 200 and 100 thousand years ago. They
are much more gracile than earlier groups (such as Neanderthals and other hominins of the time—
H. erectus and H. heidelbergensis) and share a number of physical characteristics with modern
human populations:
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Smaller face, with prominent chin
Rounded skull, with a high forehead
Increasingly gracile postcranial morphology
Interaction between Neanderthals and modern humans has been suggested on the basis of findings
in the Middle East. Two of the oldest modern sites (Skhul and Qafzeh) were discovered in close
spatial (and overlapping temporal) proximity to Neanderthal sites (Tabun, Amud, and Kebara).
However, it remains uncertain what type of real interaction occurred between the groups. But
between 40 and 30 kya the Neanderthals disappeared, evidently replaced by essentially modern
humans.
The Upper Paleolithic
Upper Paleolithic technology, culture, and behavior appears in the archaeological record sometime
after 45 kya. Some of these differences, in comparison to earlier technologies, are the following:
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Larger, more elaborate (specialized) tool kit
Use of bone, antler, and other materials, in addition to stone
Production of ornamental artifacts
Construction of elaborate shelters
Increased use of exotic (nonlocal) raw material in tool making
The first modern humans found in Europe were called the Cro-Magnons (see Fig. 14-1 for general
cranial traits). While the individuals found at Cro-Magnon in France in particular were not the
earliest inhabitants of Europe, it appears as though people very similar to the Cro-Magnons
precipitated the sudden disappearance of Europe's previous inhabitants, the Neanderthals
Figure 14.1 Cranial features of modern humans.
Image Credit: W.W. Norton
Upper Paleolithic technologies spread to many regions, including Australia, by 40 kya. Upper
Paleolithic technology is not found in southern Asia until many years later (at about 30 kya) and
signs of modern humans are scarce. Yet, it remains a possibility that undiscovered sites exist in the
region, since Upper Paleolithic industries inevitably passed through the region. However, crude
stone tools remain common in southern Asia.
Modern Behavior
Modern humans who used Upper Paleolithic technology continued to live in a manner not unlike
that of Neanderthals; however, they were able to exploit a wider range of resources and different
environments. This technological advantage is expected to have manifested itself in the
demographics of Upper Paleolithic cultures:
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Upper Paleolithic modern humans lived at much higher population densities than
Neanderthals.
They lived longer than Neanderthals.
They incurred fewer instances of injury and disease.
What then, is the basis of this sudden modernization that became such a successful strategy for H.
sapiens? One argument suggests that the change began at the genetic level, creating a biological
template that facilitated modern behavior. These changes would be indubitably cognitive in nature
and are not likely to materialize in the fossil record. Another argument suggests, though, that the
human revolution came as a result of cultural evolution and that the hiatus between the emergence
of modern humans and the appropriate behavior was merely a period of cultural development and
accumulation.
Origin and Spread of Modern Humans
Two principal models have been suggested to address the emergence of modern humans, although
there are other models that borrow from both extremes. One is the model arguing that modern
humans evolved in Africa and spread out, replacing earlier hominin groups. The other model argues
that modern humans arose gradually in many different areas from morphologically varied “archaic
Homo sapiens,” although evidence for the replacement model has severely challenged this
conception in the last few years. The central question that both these models address concerns the
manner in which modern humans emerged. So, when the behaviorally modern humans left Africa,
did they emerge as a single unit and spread throughout the world? Also, when these humans
contacted existing groups (such as Neanderthals and H. erectus), did these populations experience
gene flow through interbreeding, or was there a population replacement?
The older model argues that ancient regional populations maintained species continuity with
modern humans through gene flow. Continuous morphological variation can be examined from
modern to archaic populations suggesting that these groups exist up to the present day. This
morphological continuity is most compelling in samples of ancient and modern groups from East
Asia.
The model taken from recent genetic evidence argues for no gene flow or interbreeding. Because of
relative homogeneity in the human genome, as well as a lack of unique regional genes, geneticists
and some anthropologists argue that all modern-day human beings emerged from an African
population sometime between 100 and 200 thousand years ago.
The genetic evidence supporting the replacement model has become more robust in recent years.
First, mitochondrial DNA (DNA that is outside of the nucleus and inherited solely through the
maternal line—mitochondria on sperm do not get incorporated into the zygote) calculations of
difference between living people have been used to estimate how long it took these differences to
evolve. Such data indicate that all humans living today descended from a common population that
lived on the continent of Africa between 200 and 100 kya.
Humans, in general, are less genetically variable than other primates, another strong suggestion that
we have a fairly recent origin. Not only that, but contemporary Africans are the most genetically
variable of all human groups. Simply speaking, two Africans are more likely to be genetically
different from each other in terms of their mitochondrial DNA than any two other people on the
earth. This compelling discovery places the original human population explosion smack dab in
Africa. Why? If contemporary non-African groups represent the branching from a few, migrating
African populations, that means that there was a significant amount of genetic diversity between
isolated groups remaining on the African continent after the founding populations of Europe, Asia,
and Australia departed. Additionally, other lines of genetic data, such as patterns of mutations on
the Y chromosome (possessed only by men) also converge on the conclusion of a recent African
origin for our entire species.
Beyond the examination of genetic evidence for replacement, if in fact earlier populations did
indeed interbreed with modern groups as the multiregional model suggests, novel genes would be
expected in these regions. Yet none have been found. In addition, the lack of genetic diversity
indicates a time of low population, possibly a bottleneck, without sufficient time to regain variation
through mutation. Last, DNA recently extracted from a Neanderthal fossil place the last common
mitochondrial ancestor of Neanderthals with modern humans at approximately 500 kya, seemingly
too long ago to guarantee a significant genetic contribution from the Neanderthals to the modern
human lines. However, this does not exclude the possibility that interbreeding occurred between
Neanderthals and moderns. Further, DNA that is tens of thousands of years old is typically
contaminated with modern DNA, and researchers are only able to obtain the smallest of segments as
usable samples.