Tuesday, September 2, 2014

Human Evolution - Out Of Africa, Assimilation, Multi-Regionalism

So much has happened in the field of human evolution in the last few years!

Two end member theories have been popular for some time. The Out Of Africa theory says that modern humans originated in Africa around hundred thousand years ago and then spread all over the world replacing local populations of humans from older migrations. On the other hand the multiregional scenario said that modern humans did not originated exclusively in Africa. Rather modern humans evolved from local populations everywhere i.e. eg. modern Chinese evolved from Homo erectus  (which migrated there from Africa several hundred thousand years ago) in China with some gene flow between regions.

That extreme multiregionalism has now been rejected by recent advances in understanding genetic relationships between human populations but in a way so has the extreme Out of Africa version. There is evidence now that modern humans interbred with older regional populations as they spread across the world. This is now termed Out of Africa with assimilation or as "leaky replacement" by some.

Chris Stringer a researcher at the Natural History Museum London writes a good summary of the various theories of modern human origins. It is open access and worth reading.

A short excerpt:

 ‘Modernity’ was not a package that had a single African origin in one time, place, and population, but was a composite whose elements appeared, and sometimes disappeared, at different times and places and then coalesced to assume the form we see in extant humans [6]. However, during the past 400 000 years, most of that assembly took place in Africa, which is why a recent African origin still represents the predominant (but not exclusive) mode of evolution for H. sapiens. Rather than saying ‘we are all multiregionalists trying to explain the out-of-Africa pattern’ [1], it would be more appropriate to say ‘we are all out-of-Africanists who accept some multiregional contributions’.


  1. Suvrat - your opening comment is certainly true! One of the many strands of research beyond my normal realms that I pursued for the new book was, indeed, the current state of affairs in human evolution. I wanted to be able to talk about the role of arid lands as barriers and corridors in the whole story (Saharan rivers etc.) and I was fascinated to find how complex and controversial the whole field remains. My old simple-minded 'out of Africa' assumptions had to be fundamentally modified, and the whole exercise took a great deal of - very enjoyable and interesting - reading.

    This paper is a great summary - thanks. I particularly enjoyed the discussion of the implications of hybridisation, species definitions and 'reticulation'. I found myself, when writing the human evolution discussion, referring back to Steve Gould when he wrote:

    "Humans are not the end result of predictable evolutionary progress, but rather a fortuitous cosmic afterthought, a tiny little twig on the enormously arborescent bush of life, which if replanted from seed, would almost surely not grow this twig again."

    I rather enjoy thinking of myself as a "tiny little twig on the enormously arborescent bush of life"!

  2. Good thoughts Michael.. and thanks for reminding me of Stephen Gould's comment!