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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.

One thought on “Dispersal

  1. Very interesting post. High variation starts showing up in the genus Homo, and some would consider variation an incredibly important driver in human evolution (2012-“Plasticity in Human Life History Strategy” by Kuzawa & Bragg). While there is variation between populations, variation within populations is much greater (Fst ~.1), indicative of high gene flow. Another fact that I think is important to consider is the incredible range beginning with Homo erectus, which likely increased incidents of populations interacting and thus genes flowing. However, DNA analysis does tend to support modern human origins of 150,000-200,000 in Africa. Personally, I find myself somewhere in the middle. It seems reasonable that there was quite a bit of gene flow between many populations, at the same, it also seems reasonable that there was less gene flow between some populations. For example, the Neandertals were fairly isolated in Europe (though they also lived in Asia). There is evidence of gene flow (Most Europeans have ~2% Neandertal DNA), but not a whole lot. This topic is incredibly dynamic and full of research questions waiting to be tested. I wish I had talked to Dr. Caspari about this more as an undergraduate, but most of what we talked about was our mutual interest in race (she has written extensively on race and the history of physical anthropology, and wrote an incredibly long book on race and human evolution with Dr. Wolpoff that I hope to find time to read eventually).

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