Behavioral and Biological Origins of Modern Humans
by Dr. Richard G. Klein
To begin Dr. Klein's talk you can click here or read this brief overview, below, that provides links to the best places in the talk for specific topics.
Two theories dominate current thinking on the origin of modern
humans. The first, often known as the "out -of-Africa"
theory, posits that from at least one million years ago, human
populations followed different evolutionary trajectories on different
continents, culminating by 100,000 years ago in the emergence
of a least three continentally distinct human populations.
In the Far East, there were the still poorly documented nonmodern
people who probably represent an evolved end product of Homo
erectus; in Europe, there were the equally nonmodern Neanderthals;
and in Africa, there were modern or near-modern humans.
In its most extreme form, the "out-of-Africa" theory
posits that modern people expanded from Africa, beginning 60,000-50,000
years ago, and replaced the Neanderthals and equally archaic east
Asians without gene exchange or inter breeding. In its less extreme
form, "out-of-Africa" allows for some gene flow between
expanding moderns and resident archaic populations.
The primary alternative to "out-of-Africa" is the
theory of multiregional evolution, which postulates that
modern humans originated essentially everywhere--in Africa, but
also in Europe and Asia--where non-modern humans had lived previously.
Proponents of the multiregional model agree that widely dispersed
human populations tended to diverge morphologically from the time
they first colonized Eurasia(one million years ago or before),
but they argue that continuous gene flow ensured the rapid
spread of highly adaptive novelties (like larger brains) and thereby
kept all human populations on the same fundamental evolutionary
track toward modern people.
It is still possible to argue about these theories, but burgeoning
fossil, archeological, and genetic evidence
now supports the "out-of-Africa" theory far more