http://www.sciencedirect.com/science/article/pii/S0191886912000840 Do pigmentation and the melanocortin system modulate aggression and sexuality in humans as they do in other animals? Abstract Pigmentation of the hair, skin, cuticle, feather and eye is one of the most salient and variable attributes of vertebrates. In many species, melanin-based coloration is found to be pleiotropically linked to behavior. We review animal studies that have found darker pigmented individuals average higher amounts of aggression and sexual activity than lighter pigmented individuals. We hypothesize that similar relationships between pigmentation, aggression, and sexuality occur in humans. We first review the literature on non-human animals and then review some of the correlates of melanin in people, including aggression and sexual activity. Both within human populations (e.g., siblings), and between populations (e.g., races, nations, states), studies find that darker pigmented people average higher levels of aggression and sexual activity (and also lower IQ). We conceptualize skin color as a multigenerational adaptation to differences in climate over the last 70,000 years as a result of “cold winters theory” and the “Out-of-Africa” model of human origins. We propose life history theory to explain the covariation found between human (and non-human) pigmentation and variables such as birth rate, infant mortality, longevity, rate of HIV/AIDS, and violent crime. Highlights ► In 40 species of wild vertebrates, darker pigmented individuals are more aggressive and sexually active. ► Cross fostering studies and pharmacological dose manipulations establish the role of the melatonin system. ► We review the human literature within and between populations and find similar relationships with pigmentation. ► Darker individuals average higher levels of crime, sexual activity including HIV/AIDS, and lower IQ.