Violence in men can be explained by traditional theories of sexual selection. In a review of the literature, Professor John Archer from the University of Central Lancashire, a Fellow of the British Psychological Society, points to a range of evidence that suggests that high rates of physical aggression and assaults in men are rooted in inter-male competition.

These findings are presented April 18 at the British Psychological Society Annual Conference held at the Grand Connaught Rooms, London (18-20 April).

Professor Archer describes evidence showing that differences between men and women in the use of physical aggression peak when men and women are in their twenties. In their twenties, men are more likely to report themselves as high in physical aggression, and to be arrested for engaging in assaults and the use of weapons, than at any other age. They also engage in these activities at a phenomenally higher rate than women.

Professor Archer highlights that sex differences in aggression are not observed in relation to indirect forms of aggression but become larger with the severity of violence. Indeed, at the extreme end of violence, there are a minimal number of female-female homicides in the face of a high male-male homicide rate. Interestingly, men are also much more likely to engage in risky behaviour in the presence of other men.

Professor Archer says that a range of male features that develop during adolescence arising from hormonal changes in testosterone accentuate aggressive behaviour. Examples include the growth of facial hair, voice pitch and facial changes such as brow ridge and chin size. He implicates height, weight and strength differences between men and women as further evidence of male adaptation to engage in fighting.

How does the environment influence aggression and violence? Professor Archer suggests there are two key principles -- unequal wealth and a high ratio of sexually active men to women -- that may increase physical aggression and violence in young men.

Professor Archer says: "The research evidence highlights that societal issues such as inequality of wealth and competition between males may contribute to the violence we see in today's society."