how continuous variation from one geographic area to another), widely separate human populations are marked by a number of physical differences. Most of these differences represent adaptations to local environmental conditions; a process that some scientists believe began with the spread of Homo erectus sometime after a million years ago. In their view, human development since Homo erectus has been one continuous, in-position evolution, meaning, local populations have remained, changing in appearance over time. What they are trying to say is that the peopling of the world, the spreading of humans, has not changed since Homo Erectus. The Neanderthals and other early Homo sapiens are seen as descending from Homo erectus and are ancestral to modern humans. Other scientists view racial differentiation as a relatively recent phenomenon. In their opinion, the features of the Neanderthals, which are a low, sloping forehead, large brow ridge, and a large face without a chin are too primitive for them to be considered the ancestors of modern humans. They place the Neanderthals on a side branch of the human evolutionary tree that became extinct. According to this theory, the origins of modern humans can be found in southern Africa or the Middle East. Evolving perhaps 90,000 to 200,000 years ago, these humans then spread to all parts of the world, supplanting the local, earlier Homo sapiens populations. In addition to some fragmentary fossil finds from southern Africa, support for this theory comes from comparisons of mitochondria DNA, a DNA form inherited only from the mother, taken from women representing a worldwide distribution of ancestors. These studies suggest that humans derived from a single generation in southern Africa or southeastern Asia. Because of the tracing through the material line, this work has come to be called the “Eve” hypothesis. Most scientists, who consider the human race to be much older, do not accept its re...
