Sexual violence in the United States and the role of season.

An analysis by the cosinor method of over 50,000 rapes in 16 different locations in the United States revealed statistically significant annual rhythms in 14 locations, with maxima in the summer. Changes in numbers of rapes and assaults showed similar seasonal patterns, suggesting that rape comprised a subcategory of aggressive behavior. In contrast, there was a virtual absence of seasonal changes in numbers of murders. A close relation emerged between assaults and rapes, on the one hand, and temperature, on the other, in different geographical locations. The authors hypothesize that human violence, just like aggression in nonhuman primates, is influenced by exteroceptive environmental factors.