Wednesday, December 10, 2008

Distance from Africa explains within-population cranial variation better than climate

This paper is somewhat disappointingly deceptive (as Dienekes points out nicely). They are actually looking at within-population variation in cranial traits and how it varies across the globe. They could have put that in their title.
To be fair, I haven't looked too closely at the paper, and it does look interesting and informative as to the relative roles of demographic vs. selection forces in shaping within-population variation.

Distance from Africa, not climate explains human variation.
Lia Betti, Fran├žois Balloux, William Amos, Tsunehiko Hanihara, Andrea Manica
Proc Roy Soc B Early online
Abstract: The relative importance of ancient demography and climate in determining worldwide patterns of human within-population phenotypic diversity is still open to debate. Several morphometric traits have been argued to be under selection by climatic factors, but it is unclear whether climate affects the global decline in morphological diversity with increasing geographical distance from sub-Saharan Africa. Using a large database of male and female skull measurements, we apply an explicit framework to quantify the relative role of climate and distance from Africa. We show that distance from sub-Saharan Africa is the sole determinant of human within-population phenotypic diversity, while climate plays no role. By selecting the most informative set of traits, it was possible to explain over half of the worldwide variation in phenotypic diversity. These results mirror those previously obtained for genetic markers and show that ‘bones and molecules’ are in perfect agreement for humans.

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