August 27, 2012

When Eurasians got lighter skin

My default position is to doubt all molecular dates until I understand how they were derived. Nonetheless, these results seem broadly consistent with the idea that Eurasian modern humans got lighter as their ancestors moved into more northern latitudes of the Old World and replaced Neandertals and others earlier Eurasian occupants, and then they got really lighter post-LGM, and then some got really really lighter with mutations in genes such as SLC24A4 (not studied here).

I suppose we will really find out who got what mutation when only through ancient DNA.

Mol Biol Evol (2012) doi: 10.1093/molbev/mss207

The timing of pigmentation lightening in Europeans

Sandra Belezal et al.

The inverse correlation between skin pigmentation and latitude observed in human populations is thought to have been shaped by selective pressures favoring lighter skin in order to facilitate vitamin D synthesis in regions far from the equator. Several candidate genes for skin pigmentation have been shown to exhibit patterns of polymorphism that overlap the geospatial variation in skin color. However, little work has focused on estimating the timeframe over which skin pigmentation has changed and on the intensity of selection acting on different pigmentation genes. To provide a temporal framework for the evolution of lighter pigmentation, we used forward Monte Carlo simulations coupled with a rejection sampling algorithm to estimate the time of onset of selective sweeps and selection coefficients at four genes associated with this trait in Europeans: KITLG, TYRP1, SLC24A5, and SLC45A2. Using compound haplotype systems consisting of rapidly evolving microsatellites linked to one SNP in each gene, we estimate that the onset of the sweep shared by Europeans and East Asians at KITLG occurred about 30,000 years ago, after the out-of-Africa migration, while the selective sweeps for the European-specific alleles at TYRP1, SLC24A5, and SLC45A2 started much later, within the last 11,000-19,000 years, well after the first migrations of modern humans into Europe. We suggest that these patterns were influenced by recent increases in size of human populations, which favored the accumulation of advantageous variants at different loci.

Link

5 comments:

Solís said...

Interesting.

I really see no reason why humans living in the southern and central parts of Europe during the Last Glacial Period would have had brown skin instead of an olive type of skin color. Though I'm still sure they had dark hair and brown eyes.

So, this paper pushes back the appearance of really light skin to before the dawn of the Neolithic. It seems that the LGM acted as a natural selector of sorts and made humans develop lighter skin after it ended.

It also seems that agriculture is no longer an explanation for the appearance of fair traits.

wagg said...

Solis: "I really see no reason why humans living in the southern and central parts of Europe during the Last Glacial Period would have had brown skin instead of an olive type of skin color. Though I'm still sure they had dark hair and brown eyes."

Since the highest frequency of light eyes, hair and skin in north Africa is also where (in the Moroccan Rif) were found many "west eurasian" mtDNA haplogroups possibly having a link with Europe for a non-negligible number of them (Kefi et al. 2005, study about the Taforalt population more than 12,000 yrs ago) in populations having a Cro-magnon-like morphology (Mechtoids) and having likely a cultural link with Iberia (Ibero-maurusian culture/Oranian culture), present during the Paleolithic period, I definitely wouldn't want to be too sure of anything in that matter, as of now.

Dr Rob said...

Yes, but what about when others developed 'darker' skin ??

eurologist said...

Multiply the dates by a factor of two or so, and they become more believable.

Skin color is so highly variable and selected for - there's no reason humans stuck around tens of thousands of years with the "wrong" color (for their geography). Native Americans demonstrate this nicely.

Tobus said...


Native Americans demonstrate this nicely.

How so?