If the out-of-Africa theory is correct and modern humans left Africa where do divergent human species, such as Neanderthal come from? Why does DNA from these divergent human species appear in our DNA? What accounts for the differences between racial groups (i.e. why are Asians on average thinner than Northern Europeans?)

Hi Rose
The presence of Neandertal DNA among living humans is usually ascribed to interbreeding between Homo sapiens and Neandertals.
Keep in mind that biologists speak of two different kinds of "species", species defined on the basis of their morphology and species defined the basis or their inability to interbreed with one another.  Both kinds of species reflect genetic differences, but in the fossil record it is rare to be able to infer reproductive activities.  One can only do this with rarely preserved DNA from fossils.  The situation is much like among wolves and coyotes.  The two differ morphologically and behaviorally, but they can interbreed with one another.
Thinness among Asians vs. Northern Europeans is probably not just genetic, it probably reflects diet and sexual selection among other factors. Here in the US obesity is as much a problem for Asians as it is for Europeans.
John Shea


All Answers

Answers by Expert:

Ask Experts


John Shea


Questions about Old World prehistoric archaeology (especially Stone Age) of Europe, Africa, and Western Asia, prehistoric human and hominid behavior, primitive technology, origin of modern humans, extinction of the Neandertals. IMPORTANT: Between February 14 and September 01, 2014, I will be on sabbatical leave. During this time I will have limited access to email. This means that there may be very long periods (i.e., weeks) between your posting a question and my having time to answer it.


>20 years as a professional anthropologist based at a research university.

Journal of Field Archaeology, Journal of Archaeological Science, Lithic Technology, Evolutionary Anthropology, Current Anthropology, Mitekufat HaEven (Journal of the Israel Prehistoric Society), Paléorient, Annual of the Department of Antiquities of Jordan, American Anthropologist, Geoarchaeology.

Ph.D (Anthropology) Harvard University, 1991.
BA (Archaeology) Boston University, 1982.

Awards and Honors
Sigma Xi Distinguished Lecturer 2012-2014

©2016 All rights reserved.