From Geographic distribution of environmental factors influencing human skin coloration:

...The UVR [ultraviolet radiation] data recorded by satellite were combined with environmental variables and data on human skin reflectance in a geographic information system (GIS). These were then analyzed visually and statistically through exploratory data analysis, correlation analysis, principal components analysis, least-squares regression analysis, and nonlinear techniques. The main finding of this study was that the evolution of skin reflectance could be almost fully modeled as a linear effect of UVR in the autumn alone. This linear model needs only minor modification, by the introduction of terms for the maximum amount of UVR, and for summer precipitation and winter precipitation, to account for almost all the variation in skin reflectance.....

The map above was generated from the regression analysis. Apparently it has been updated as of 2007 (received the link from a friend). It does look much better than it did in the original paper (which I have read and have a PDF copy of). Do note that the selection of peoples whose reflectance values were plugged into the model obviously matters. But I still think it's interesting the sort of predictions this map produces and how it fits with our intuitions of what the distributions should be, and the knowledge of what they are. Note the equivalent latitudes in Europe and North America, or Australia.

Labels: human biodiversity, Pigmentation