Annual rhythms in human violence and sexual aggression in the United States and the role of temperature

Violent crimes committed during two to three consecutive years in sixteen different locations in the United States were examined for annual rhythms using the cosinor method of analysis. Annual changes in rapes and in the more numerous aggravated assaults were highly significant in the majority of locations. They were closely related to each other in time and showed maxima generally between July and August. The data suggest that rape may comprise a subpopulation of assaultive behavior. In contrast, there were seasonal rhythms for robbery in only five locations with maxima between November and December. There was a virtual absence of any seasonal changes in murder. A close statistical association was established between annual assault and rape rhythms and annual temperature fluctuations in the different locations. This finding suggested that certain aspects of human violence may be influenced by exteroceptive factors.