Some updates on the evolution of variation in human skin pigmentation (pp. 117-121). A number of the genes which contribute to light skin are known. Norton et al. (2008) used molecular techniques to look at the frequencies of alleles of these genes in different human populations, and to infer whether certain alleles had been under recent selection. They showed that alleles associated with light skin had been under strong selection in both Europeans and in East Asians. However, the light skin of East Asians is actually due to a different set of mutations than the light skin of Europeans. This means that light skin is an example of convergent evolution; two branches of humans left the tropics moving towards the North Pole, and independently evolved pale skins through slightly different mutations.

The story gets even better, because we now have so much of the sequence of the Neanderthal genome (see page 245). Recall that the Neanderthals are another group of humans who moved out of Africa into Northern climes, albeit hundreds of thousands of years before our direct ancestors. The adaptive story outlined on pages 117-21 would suggest that there would be a selective pressure on them to evolve light skins, for the same reasons as modern Europeans and East Asians have. Lazuela-Fox et al. (2007) sequenced a gene which regulates melanin production from two Neanderthal skeletons. It’s a mutation to this gene which gives us the red hair and very pale skin of some European living humans.  The Neanderthals had a different mutation to this gene, one not found in any living human population, but whose effect the researchers were able to show is to dramatically reduce melanin production. Thus, the Neanderthals would have almost certainly had pale skin and red hair, but because of different mutations than those which give living Europeans this complexion. ‘Blondeness’ has evolved convergently in European at least twice in the last few tens of thousands of years.

Lazuela-Fox, C. et al. (2007). A melanocortin 1 receptor allele suggests varying pigmentation among Neanderthals. Science 318: 1453-5. [DOI: 10.1126/science.1147417]

Norton, H.L. et al. (2008). Genetic evidence for the convergent evolution of light skin in Europeans and East Asians. Molecular Biology and Evolution 24: 710-22. [DOI: 10.1093/molbev/msl203]