In a recent post, I described how women are catching up on men in terms of criminal violence. Yet, the difference remains large and calls for explanation. Much of the gender difference is explainable in terms of male sexuality and societies where men compete directly for mates have more criminal violence.

Violent Crimes Linked to Sexual Competition Between Men

Assault, rape and murder are the most serious crimes of violence but they have another common denominator: each is connected to sexual competition. The connection between criminal violence and sexuality is easily made in terms of the characteristics of offenders.

Most of the violent crime is committed by young men who are actively pursuing mates or sex partners. More than none-tenths of violent crimes are committed by men.

Physical aggression is one aspect of sexual competition amongst men (as it is for other male mammals), but less so amongst women. Women compete by enhancing their dress and appearance so as to appeal to men (1) or by criticizing a competitor.

Research on homicides in Detroit found that most of them were triggered by “trivial altercations” such as who is next in line at a grocery store, or whether one person purposely jostled another in a bar (2). Of course the altercation is not “trivial” when someone ends up dead and evolutionary psychologists believe that these (mostly) young men are actually fighting for status in their peer group because high-status individuals are more sexually attractive to women.

In pre-industrial societies competition over women is the biggest cause of male homicides (3) outside of warfare. Sexual jealousy is the biggest cause of women being killed by husbands or lovers (2).

One of the more controversial links between violent crime and sexuality is testosterone. Men commit most violent crime at ages when testosterone peaks in the late teens and early twenties. Intriguingly,

after men divorce and begin dating again their testosterone level jumps – and so does their involvement in violent crime (4). Another link between violent crime and sexuality is the fact that adverse marriage markets for women that encourage more premarital sex also increase violent crime.

Violent Crime and the Marriage Market

Women commit far fewer serious crimes of violence than men. One reason for the gender difference may be that women mostly express aggression either verbally, through indirect means (e. g., breaking plates), or via non lethal methods (e. g., slapping).

Although men commit far more violent crimes than women, societies with a lot of males relative to females have lower crime rates according to my cross-national research on assaults, homicides and rapes (5). Conversely, societies with a lot of females have more violent crime. This result seems baffling but it can be explained in terms of differences in male sexual behavior in different countries.

Societies with an excess of females have more extra marital sex because males are in the driving seat and they prefer sex earlier in a relationship. With more competition over female sex partners there are more reasons for male-on-male assaults and homicides. Sexual crimes against women increase as well. Women are statistically more likely to be raped if they go out alone at night to bars and nightclubs than if they stay home with their parents or spouse.

In societies with a lot of men, there is little dating and women rarely go out alone at night unless they happen to be sex workers. In extreme cases, such as Saudi Arabia, women are not allowed to leave the house without the permission of a male relative. This means that they are less vulnerable to being raped, whether by strangers, or by dates.

Violent crime is thus a great deal more interwoven with sexual behavior than most people would think and this pattern is one of the best ideas we have for explaining country differences in criminality. For instance it accounts for higher crime rates in Latin America compared to other regions in the world, a phenomenon that has no other satisfactory explanation (and is not due to the prevalence of organized crime, 6). This region has a relative excess of men and very high levels of extramarital sexuality as illustrated by a high proportion of births to single women.


1. Barber, N. (2002). The science of romance. Buffalo, NY: Prometheus.

2. Daly, M. and Wilson, M. (1988). Homicide. Hawthorne, NY: Aldine de Gruyter.

3. Symons, D. (1979). The evolution of human sexuality. New York: Oxford University Press.

4. Mazur, A., & Michalek, J. (1998). Marriage, divorce, and male testosterone. Social Forces, 77, 315-330.

5. Barber, N. (2000b). The sex ratio as a predictor of cross-national variation in violent crime. Cross-Cultural Research, 34, 264-282.

6. Barber, N. (2006b). Why is violent crime so common in the Americas? Aggressive Behavior, 32, 442-450.

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