Friday, 9 November 2007

Neanderthal Redheads?

Recently, a Spanish team has analyzed the bones of two Neanderthals and recovered the MC1R gene—the one that controls hair color and, in the case of red hair, lightens skin color. Their findings? First, both of the Neanderthals had an MC1R variant unlike any that now exist in modern humans. This pours cold water on the idea that the unique hair colors of modern Europeans are due to Neanderthal intermixture. Second, the MC1R variant looks like a ‘loss-of-function’ allele, much like the ones that now produce red hair.

According to the lead author, “In Neanderthals, there was probably the whole range of hair colour we see today in modern European populations, from dark to blond right through to red” (Rincon, 2007). Well, maybe yes, but maybe no. Europeans have a diverse palette of hair colors because their MC1R gene has at least 11 functionally different alleles—and not because a new allele replaced the original African one. In fact, the ‘African’ allele is still common in Europe.

Will the Neanderthals be shown to have many MC1R variants, just like modern Europeans? The lead author seems to think so, as does Dr Clive Finlayson, director of the Gibraltar Museum, who says that Neanderthal and modern European hair color may reflect a common “propensity towards the reduction of melanin in populations away from the tropics. … a good example of parallel, or convergent evolution - a similar evolutionary response to the same situation” (Rincon, 2007). Melanin was reduced because there was less natural selection for dark skin (i.e., for protection against solar UV) and more for light skin (i.e., for vitamin D synthesis).

Neither selective pressure, however, would have diversified hair color, at least not that of modern Europeans:

1. When there is less selection for dark skin, ‘loss-of-function’ variants will proliferate at any gene associated with skin color. But such proliferation needs about a million years to produce the hair-color variability that Europeans now display, including c. 80,000 years to produce just the current prevalence of red hair (Harding et al., 2000; Templeton, 2002).

2. When there is more selection for light skin, the original allele at any one gene will be replaced by an allele that optimally reduces skin pigmentation. But the overall number of alleles will remain the same.

Moreover, if we examine the many homozygous and heterozygous combinations of hair color (MC1R) alleles, most have little visible effect on skin pigmentation, except for the ones that produce red hair (Duffy et al., 2004). It is difficult to see how either relaxed selection for dark skin or increased selection for light skin could have given rise to most of these alleles, especially over such a short span of evolutionary time.

It was probably another selective pressure that diversified European hair color. Sexual selection is especially likely because it is known to produce bright color traits, especially polymorphic ones.

Sexual selection is also indicated by the geographic distribution of hair-color diversity. During the last ice age, particularly on the steppe-tundra of northern and eastern Europe, a unique demographic environment intensified sexual selection of women by reducing the supply of men and by limiting polygyny. Hunters die in proportion to the distances they cover, and hunting distance was at a maximum on these open plains with their dispersed and highly mobile herds. Since women depended on men for sustenance, there being little food to gather on the tundra, only the ablest hunter could provide for multiple wives. Result: too many women competing for too few men. In a saturated, competitive market, success hinges on visual merchandising; therefore, a woman with a bright, novel color would have attracted attention and edged out otherwise equal but bland rivals. It is this sexual selection for both brightness and novelty that may have multiplied the number of hair color alleles among early modern Europeans.

This demographic environment was unknown to the Neanderthals. Unlike early modern Europeans, they never colonized the steppe-tundra of northern and eastern Europe under ice age conditions:

When temperatures declined during the Early Pleniglacial (OIS 4), the Neanderthals were apparently unable to cope with periglacial loess-steppe environments on the East European Plain. Much of the latter seems to have been abandoned by Neanderthals at this time, although some areas (notably the southwest regions) were reoccupied during the milder Middle Pleniglacial (OIS 3). By contrast, modern humans successfully colonized the periglacial loess-steppe during the terminal phases of OIS 3 and the subsequent Last Glacial Maximum (OIS 2). (Hoffecker, 2002, p. 136)

The Neanderthals also seem to have been characterized by relatively limited movements and small territories in comparison to recent hunter-gatherers in northern latitudes. (Hoffecker, 2002, p. 135).

These archaic humans seem to have occupied a niche that excluded hunting of herds over expanses of steppe-tundra. Among the many environments that modern humans colonized, this seems to be the one that most intensified sexual selection of women—by reducing both the supply of men and their demand for mates.

So I doubt that the Neanderthals had a wide range of hair colors. They probably all sported the same reddish coat. Coat? Yes, you read right. They were as furry as bears. How else did they survive in subzero temperatures without tailored clothing? (Hoffecker, 2002, pp. 107, 109, 135, 252). Moreover, both needles and the human body louse (which lives in clothing) seem to date back no earlier than 50,000 years ago, i.e., the transition from Neanderthals to modern humans (Harris, 2006).

References

Duffy, D.L., Box, N.F., Chen, W., Palmer, J.S., Montgomery, G.W., James, M.R., Hayward, N.K., Martin, N.G., and Sturm, R.A. (2004). Interactive effects of MC1R and OCA2 on melanoma risk phenotypes. Human Molecular Genetics, 13, 447-461.

Harding, R.M., Healy, E., Ray, A.J., Ellis, N.S., Flanagan, N., Todd, C., Dixon, C., Sajantila, A., Jackson, I.J., Birch?Machin, M.A., and Rees, J.L. (2000). Evidence for variable selective pressures at MC1R. American Journal of Human Genetics, 66, 1351?1361.

Harris, J. R. (2006). Parental selection: A third selection process in the evolution of human hairlessness and skin color. Medical Hypotheses, 66, 1053-1059.

Hoffecker, J.F. (2002). Desolate Landscapes. Ice-Age Settlement in Eastern Europe. New Brunswick: Rutgers University Press.

Laleuza-Fox, C., Römpler, H., Caramelli, D., Stäubert, C., Catalano, G., Hughes, D., Rohland, N., Pilli, E., Longo, L., Condemi, S., de la Rasilla, M., Fortea, J., Rosas, A., Stoneking, M., Schöneberg, T., Bertranpetit, J., Hofreiter, M. (2007). A Melanocortin 1 receptor allele suggests varying pigmentation among Neanderthals. Science. doi:10.1126/science.1147417.

Rincon, P. (2007). Neanderthals 'were flame-haired'. BBC.co.uk. October 25, 2007.

Templeton, A.R. (2002). Out of Africa again and again. Nature, 416, 45-51.

3 comments:

Slaughter said...

Red hair is not from Neanderthals. Pity, it would explain something.
I live near an area with the highest rate of of red hair in the world. I have watched a lot of U.S. television and as far as I can see people have a low opinion of red hair all over the world. Judas was supposed to be red haired in some traditions but who knows that today, and the belief is significant. Natural red hair is eye catching, and as an unusual colour, should it not be more valued according to your explaination for it.
Red headed women are not considered attractive, why?

Slaughter said...

Eurika (maybe),I just thought of something.
Having seen more Redheaded women in the flesh that many others I may have had an advantage, I am proud of my Evo and Proud thinking, here goes - ruddy skin.

Tod said...

If they were as "furry as bears" and living in "subzero temperatures" (meaning little sunlight presumably), how did the UVB get through to make Vitamin D for these hairy handed gents? It didn't, they got it from animal livers obvously, so why would anyone think modern Europeans needed to loose melanin.