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EVIDENCE FOR 13,000 YEARS OF RELAXED SELECTION (ON INTELLIGENCE) IN WEST EURASIANS

Mai 3, 2017
Harris & Pritchard (2016) found an increased 5′-TCC-3′ to 5′-TTC-3′ mutation rate in Europeans from about 15,000 to 2,000 years ago.
Mathieson & Reich (2017) confirmed this increase for all West Eurasians. The highest increase for this type of mutation was found in a 7,000 years old European farmer, and it was found also in a 8,000 years old European hunter-gatherer, but this effect is not strongly driven by ancestry (farmer/hunter-gatherer) or by latitude, but is predicted by longitude (increasing east to west). This is in line with the increase of the mutation rate in sexual populations during range expansion found by Cobben & Kubisch (2014) and with the relaxed selection on the wave front of expansion found by Peischl (2016) in French Canadians, 6-9 generations ago. Also, Clark & Hamilton (2007) found higher fertility of Lower Class than Upper Class in French Canadians.
We know Near Easterner hunter-gatherers migrated in Europe 13,000 years ago, followed by Anatolian Neolithic farmers 9,000 years ago, and Steppe pastoralists 5,000 years ago. The relaxed selection on the front waves of these migrations could lead to a relaxed selection pressure that could favor not only the accumulation of mutations, but the increase of the mutation rate too. This is in line with the gradient east to west of the increase of the mutation rate.
 
Also, Mallick (2016) demonstrated an accumulation of mutations 5% higher in non-Africans than in Africans since the Out of Africa. The highest accumulation in Eurasians was found in West Eurasians. Most of this accumulation could produce after Last Glacial Maximum. The warming of the climate and a more sedentary life-style in Near East could relax the selection in this region. This is evidence of more permanent settlements and even of farming in Near East since 13,000 (Wilcox, 2012), 19,000 (Ramsey, 2016) and even 23,000 years ago (Snir, 2015). Also, the expansion of Near Easterners in Eurasia was not „Malthusian”, but rather resembled with the expansion of French Canadians. Furthermore, the decrease of human body size since Upper Palaeolithic is in line with the increase of the mutation rate, that is negatively correlated with the body size in mammals (Martin & Palumbi, 1993). Also, the mutation rate in mammals is higher in warmer climates (Gillman, 2009).
 
The evidence of a relaxed „general” selection is not a direct proof for a decrease of selection on intelligence. But a strong selection on intelligence could not lead to an increase of the mutation rate during 13,000 years (15,000 – 2,000 years ago), because the mutational target on intelligence is enormous. Probably genotypic intelligence decreased during this period in West Eurasia, and this is in line with Cold Winters Theory of Richard Lynn.
 
REFERENCES
Clark, G. & Hamilton, G. (2007) ECONOMIC STATUS AND REPRODUCTIVE SUCCESS IN NEW FRANCE. https://econ.ucalgary.ca/sites/econ.ucalgary.ca/files/seminars/clark%20and%20hamilton%20new%20france%202.pdf
Cobben, M.M.P. & Kubisch, A. (2014) The evolution of mutation rate in sexual populations during range expansion. bioRxiv doi: http://dx.doi.org/10.1101/008979
Gillman, L.N., et al (2009). Latitude, elevation and the tempo of molecular evolution in mammals. Proceedings of the Royal Society B 276: 3353-3359
Harris, K. & Pritchard, J.K. (2016) Rapid evolution of the human mutation spectrum. bioRxiv doi: http://dx.doi.org/10.1101/084343
Mallick, S. et al (2016) The Simons Genome Diversity Project: 300 genomes from 142 diverse populations. Nature 538(7624): 201-206. doi: 10.1038/nature18964
Martin, A.P. & Palumbi, S.R. (1993) Body size, metabolic rate, generation time and the molecular clock. PNAS 90(9): 4087–4091
Mathieson, I. & Reich, D. (2017) Differences in the rare variant spectrum among human populations. PLoS Genet 13(2): e1006581. doi:10.1371/journal.pgen.1006581
Peischl, S. et al (2016) Relaxed selection during a recent human expansion. bioRxiv doi: http://dx.doi.org/10.1101/064691
Ramsey, M.N. et al (2016) Risk, Reliability and Resilience: Phytolith Evidence for Alternative ‘Neolithization’ Pathways at Kharaneh IV in the Azraq Basin, Jordan. PLoS ONE 11(10): e0164081. doi:10.1371/journal.pone.0164081
Snir, A. et al (2015) The Origin of Cultivation and Proto-Weeds, Long Before Neolithic Farming. PLoS ONE 10(7): e0131422. doi:10.1371/journal.pone.0131422
Wilcox, G. (2012) Pre-Domestic Cultivation during the Late Pleistocene and Early Holocene in the Northern Levant. in Biodiversity in Agriculture: Domestication, Evolution, and Sustainability, editors Gepts, P. et al. Cambridge University Press
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