There are two competing hypotheses on the origin of modern humans: the Out-of-Africa hypothesis and the multiregional hypothesis. It has long been recognized that the genus Homo was the first hominid to leave Africa and disperse into other major continental areas. Evolution of the genus Homo from Australopithecus seems to be linked to global climate changes between 2 and 3 million years ago. The dispersal of Homo into the Old World was successful in part because of their increased behavioral and cognitive abilities. Both hypotheses agree that Homo erectus originated in Africa and expanded to Eurasia about one million years ago, but they differ in explaining the origin of modern humans.
The Out-of-Africa model suggests that the relatively cool, dry climate of tropical Africa presented challenging new conditions for the woodland dwelling Australopithecines. However, Homo was able to exploit new habitats, rather than just scavenger. This, mixed with their striding gait, elementary stone tools, and the simple (but expansive) pattern of scavenging resulted in successful migration out of Africa. Migration to Asia was efficient because it had fewer large primate competitors, fewer carnivorous predators, and fewer parasites and diseases. Early dispersal to Europe was not possible due large mountains and other challenging terrains.
This model then proposes that a second migration out of Africa happened about 100,000 years ago, in which anatomically modern humans of African origin conquered the world by completely replacing archaic human populations.
The multiregional hypothesis states that independent evolution occurred with some level of gene flow between continental populations occurred in the million years since Homo erectus came out of Africa. Next, natural selection was responsible for the regional variants we see today. In this model, the emergence of Homo sapiens was not restricted to any one part of the world.
Throughout my undergraduate education I learned Out of Africa exclusively. I had limited knowledge of the multiregional hypothesis until this semester. I originally thought it made little sense and was unsupported by the fossil record, however, through further investigation and extensive readings on the subject, I now support the hypothesis. Multiregional does not mean multiple origins, ancient divergence of modern populations, or parallel evolution. Instead, “it describes a worldwide network of gene exchanges, between evolving human population” (Wolpoff, et al, 2000). Gene flow accounts for diversity among groups in many modern species, therefore seems like a valid hypothesis to account to diversity among archaic populations of sapiens.
Wolpoff, M. H., Hawks, J., & Caspari, R. (2000). Multiregional, not multiple origins.