Human color vision deficiencies and atmospheric twilight

Abstract

Red‐green color vision deficiencies in human populations are generally regarded as visual dysfunctions, the frequencies of which have increased from mutational pressure and relaxation of selection in post‐Neolithic periods. However, color vision insensitivities also occur in other vertebrates and appear to be an ecological adaptation for low light levels encountered during crepuscular activity. I hypothesize a comparable function for human vision deficiencies and test this by re‐examining global frequencies of deficients in relation to photic characteristics of the habitat. Data presented here show significant positive correlations with length of atmospheric twilight and increased equatorial distance. While support for the twilight hypothesis remains equivocal, the latitudinal data imply that the high frequencies of color deficiencies in North European populations represent relatively stable frequencies from Neolithic periods when these traits were at an advantage. The data and conclusions are inconsistent with the current practice of using frequencies of these polymorphisms as cultural chronometers.