• homicide;
  • sex ratio;
  • marriage markets;
  • mating effort


Violent crimes (murders, rapes, and assaults) are substantially higher in countries with a relative scarcity of men according to research using INTERPOL data [Barber, 2000a]. This is a paradox given that males are more criminally violent and likely reflects increased direct mating competition. The present research sought to confirm and extend Barber's [2000a] finding, using murder data from the United Nations and homicides from World Health Organization that are of higher quality than the INTERPOL data, and using more rigorous controls. In addition to level of economic development, control variables included, income inequality, urbanization, population density, the number of police, and whether the country was a major center of illegal drug trafficking. Regression analyses with all controls found that killings in both data sets increased with declines in the male proportion of the population. The findings are discussed in terms of direct reproductive competition and alternative explanations are considered. Aggr. Behav. 35:49–56, 2009. © 2008 Wiley-Liss, Inc.