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Gene Frequency Clines in Europe: Demic Diffusion or Natural Selection?

Alan G. Fix
The Journal of the Royal Anthropological Institute
Vol. 2, No. 4 (Dec., 1996), pp. 625-643
DOI: 10.2307/3034300
Stable URL: http://www.jstor.org/stable/3034300
Page Count: 19
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Gene Frequency Clines in Europe: Demic Diffusion or Natural Selection?
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Abstract

According to the demic diffusion model of Cavalli-Sforza and colleagues, agriculture was spread through Europe by a rapid population expansion of early farmers from the Near East. These scholars use the presence of gene frequency clines paralleling this direction of spread to support their model. However, genetic clines may also be caused by natural selection. This article shows that the archaeological and demographic evidence for demic diffusion is questionable, and proposes an alternative selective clinal model. The model posits that genetic fitnesses changed through time as functions of increasing disease intensities brought on by the diffusion of agriculture and, especially, by the association between humans and newly domesticated animals. Since agriculture required several thousand years to spread across Europe, a gradient in duration of selection was generated. A computer simulation shows that clinal patterns similar to those observed in European populations can be produced by temporal gradients in natural selection. Thus gene frequency clines in Europe may indeed be due to domestication (specifically, to animal husbandry) but not necessarily to the mechanism of demic diffusion.

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