Chapter Review

The first modern Homo sapiens evolved in Africa between 200 and 100 kya. They are much more gracile than earlier groups (such as Neanderthals and the other hominins of the time, H. erectus and H. heidelbergensis) and share characteristics with modern human populations such as a smaller face, a prominent chin, a rounded skull, and a high forehead.

Interaction between Neanderthals and modern humans has been suggested on the basis of findings in the Middle East and genetic similarities. However, it remains uncertain what type of real interaction occurred between the groups. Between 40 and 30 kya the Neanderthals disappeared.

Upper Paleolithic technology, culture, and behavior appear in the archaeological record sometime after 45 kya. In comparison to earlier technologies, there is a larger, more elaborate tool kit made of bone, antler, and exotic materials, in addition to stone. New, ornamental artifacts are produced, and shelters are constructed.

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 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 meant that Upper Paleolithic modern humans lived at much higher population densities than Neanderthals, lived longer than Neanderthals, and had fewer instances of injury and disease.

The basis of this sudden modernization that became such a successful strategy for H. sapiens is still being debated. One argument suggests that the change began at the genetic level, creating a biological template that facilitated modern behavior. Another argument suggests, though, that the human revolution came as a result of cultural evolution.

Two principal models have been suggested to address the emergence of modern humans, often called the gradualist and replacement models. The gradualist model argues that modern humans evolved gradually in many different areas from morphologically varied "archaic Homo sapiens" and 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. On the other hand, the replacement model taken from recent genetic evidence argues for no gene flow or interbreeding, with modern humans evolving once in Africa and spreading around the world. The genetic evidence supporting the replacement model has become more robust in recent years. First, mitochondrial DNA calculations of differences between living people have been used to estimate how long it took these differences to evolve. Such data indicate that all humans living today are 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 in Africa.

Researchers have proposed different scenarios to explain the transformation of cultural behavior from Neanderthals to modern humans. In one scenario, human behavior developed quickly as a result of a key cognitive development—perhaps a shift in cognitive abilities or a result of new technologies—around 60 kya, leading to the so-called human revolution. The alternative hypothesis is that the behaviors that suddenly show up around 60 to 50 mya were actually gradually evolving in Africa since 250 kya. Researchers on either side of the debate have marshaled the fossil and archaeological evidence to bolster their own claim. More needs to be known about the ancient fossil record of Africa in this time period before a definitive theory can be drawn, but based on what we know of adaptive evolution, it is more likely that modern human behavior evolved gradually in Africa as a result of both genetic and cultural changes.