Many studies have been carried out on human
skin color variation. Here are two examples of the kind of research that has been done and their conclusions. One
article is by John Relethford, “Hemispheric Difference in Human Skin Color” and another by George
Chaplin titled “Geographic Distribution of Environmental Factors Influencing Human Skin Coloration”. Relethford’s
article discusses a study done in order to test the assumption that skin color is darkest at the equator and lighter the farther
one moves away from the equator, to the same degree in either hemisphere. This assumption is commonly held in other studies
done on human skin color. To do the test, Relethford employed a “nonlinear
piecewise regression model” to look at mean skin reflectance data from 102 males and 65 females from the Old World (449). What he found was that skin color is not the same in corresponding hemispheres and that, in fact, it is
darker in the Southern Hemisphere. Therefore, Relethford’s main argument
is that there is a difference in the “astronomical and climatic conditions “(449) of the two hemispheres which
most likely was the same in the past at different periods and that these varying conditions could have affected the way human
skin color developed.
Chaplin’s article refers to a more recent study done on the relationship between skin reflectance
and environmental variables, mostly ultra-violet radiation, to determine which played the biggest role in its development. Data on UVR was collected from NASA’s total ozone mapping spectrometer which
allowed for a measure of the “relative daily areal exposure to the ultra violet minimum erythemal dose (UVMED), i.e.,
the amount of UVR effective in causing a barely perceptible reddening of light skin” (293). Additionally, UVMED readings were given in terms of annual and seasonal averages. Data on skin reflectance
and environmental variables, such as UVR levels, were put into a geographic information system and subsequently analyzed using
a wide variety of statistical techniques. The most supported hypothesis of the
study is one that relates the evolution of skin color reflectance directly to “a linear effect of UVR in the autumn
alone” (300). Ultimately, Chaplin argues that skin color is very likely to be a human adaptation to UVR.
Human Skin Color Variation
How Do We Evaluate Skin Color Variation?
Important Conclusions and Suggestions for Further Research