What Controls Variation in Human Skin Color?

Diversity of human appearance and form has intrigued biologists for centuries, but nearly 100 years after the term “genetics’’ was coined by William Bateson in 1906, the genes that underlie this diversity are an unsolved mystery. One of the most obvious phenotypes that distinguish members of our species, differences in skin pigmentation, is also one of the most enigmatic. There is a tremendous range of human skin color in which variation can be correlated with climates, continents, and/or cultures, yet we know very little about the underlying genetic architecture. Is the number of common skin color genes closer to fi ve, 50, or 500? Do gainand loss-offunction alleles for a small set of genes give rise to phenotypes at opposite ends of the pigmentary spectrum? Has the effect of natural selection on similar pigmentation phenotypes proceeded independently via similar pathways? And, fi nally, should we care about the genetics of human pigmentation if it is only skin-deep? Why Should We Care?