Out of Africa

Posted July 23rd, 2007 by Andrea Vianello

In a recent paper by Andrea Manica, William Amos, François Balloux and Tsunehiko Hanihara published in Nature (448, 346-348, 19 July 2007, doi:10.1038/nature05951) a large study of skull measurements seems to agree with the conclusions of the existing genetic studies (e.g. Ramachandran, S. et al. 2005. Support from the relationship of genetic and geographic distance in human populations for a serial founder effect originating in Africa. PNAS 102, 15942–15947) that anatomically modern humans originate in Africa and migrated from there to all continents. It is unclear whether there was a single or multiple migrations, but all data seem to confirm the origin. An African origin of anatomically modern humans is widely accepted now, considering that Charles Roseman, an anthropologist at the University of Illinois, Urbana-Champaign, reported to Science that “Proponents of the multiregional model have been very clear for some time that their models do not posit multiple origins, as suggested in the paper”.

In short, the multiregional model proposes that genic exchanges across populations account for the development of anatomically modern humans while maintaining some regional characteristics from previous humans. In other words, such exchanges would allow for the evolution of the species and the adaptation of a population to its typical environment, making migration necessary only for limited numbers of individuals, from Africa. The populations receiving the new genes could have therefore mutated (“evolved”) rather than being replaced. Have a look at the research carried out by the Bradshaw Foundation on the topic of migration and at this website focusing on Thailand. Useful to expand knowledge on this topic, are also the Stone Age Institute and Fossil evidence for human evolution in China websites.

The debate continues, and more cutting edge research will be necessary, but at least we seem all to agree on our African origins. It seems noteworthy to me that the recent study by Manica et al. on skulls also takes in account regional variability and eliminates its influence on the published statistical analyses by including in the calculations some climate variables. By doing this, the authors admit that evolution affects populations at regional level, but consider such effects irrelevant to the genetic evolution of the species without explaining the reasons for doing this in detail. As we can see, the debate on (anatomically modern) human origins is now focusing on agreeing on minute details.