Saturday, December 6, 2008

Skin Color and Creationism

You know those creationist books that try to explain variation in human skin color by appealing to mendelian genetics? They give the impression that God created Adam and Eve with all the alleles for human skin color, and by mendelian sorting we get the modern races. You know what books I'm talking about. Just about every major creationist organization has used human skin tone to illustrate mendelian genetics in one publication or another. A recent review article by Jean Lightner addresses this idea directly, and I thought I would highlight it here, since its impenetrable title ("Genetics of Coat Color I: The Melanocortin 1 Receptor (MC1R)") is likely to put off those who might most benefit from reading it.

Jean examined the literature on coat and skin color and found that there are far more alleles than could possibly be explained by direct creation (unless God has continued to intervene and create new color alleles). The MC1R gene codes for a G-protein coupled receptor, and it regulates the production of the skin pigment eumelanin. At most, Adam and Eve could have carried only four alleles for MC1R (two alleles in each person), but now there are more than 60 human alleles! This implies that the majority of variation seen in human skin coloration is a result of some kind of mutation, which would make sense, since the whiter skin colors are associated with a nonfunctional MC1R protein.

Where did all these alleles come from? That's where Jean's paper gets interesting. Here's a snippet:
Some of these variants have been shown to be associated with an increased risk of various skin cancers, including malignant melanoma. Certainly the equatorial regions of earth have greater sun exposure which would further increase cancer risk. However, the strong selection suggested by Harding et al. (2000) appears much stronger than these factors can account for. For example, melanoma rarely strikes before the childbearing years. Lachiewicz et al. (2008) found the mean age of onset at 57 years. ... So, despite the fact that untreated melanoma is deadly, increased risk of skin cancer should not provide sufficient selection to cause the MC1R protein to be invariant in African populations. It is possible that mutation rate in the MC1R gene is affected by epigenetic factors such as sun exposure.

Provocative idea, and not so different from some things I've written [PDF]. I might also add that the timescale we're dealing with (hundreds of years instead of tens of thousands) also precludes natural selection as a significant factor in generating the diversity of human skin color.

Jean concludes her review with this idea, "This should provide creationists with strong motivation to pursue the possibility that directed mutations may often explain non-random patterns in mutations." Let's hope so. In the meantime, someone's got some books to update...

Read the full article in Answers Research Journal:

Lightner, J.K. 2008. Genetics of Coat Color I: The Melanocortin 1 Receptor (MC1R). ARJ 1:109-116.