The findings suggest that it is in a man's disposition to seek relief from stimulation by succumbing to aggressive behaviour, while women prefer the more non-aggressive line of behaviour, such as "talking things over". Maccoby and Jacklin also suggest strong evidence that aggression is an innate characteristic, by the contention that sex differences in aggression can be found early in life, at a time before social pressures may have "shaped" behaviour.
As well as innate characteristics, sex hormones have been found to play a fundamental part in the probability of aggression. If a girl is exposed to high levels of a male hormone while still a developing foetus, she will not only develop masculine genitalia, but she will also be inclined towards more masculine behaviour throughout childhood (Erhardt and Baker 1972). One hormone studied was progestin, which recent studies have shown to have a masculinizing effect on the foetus while still developing. Children, who had been exposed to the hormone while developing in the mothers" womb, were subsequently investigated in a study carried out by June Reinisch which generated evidence that males and females both exposed to the hormone were likely to act more aggressively than their non exposed siblings. The hormone had invariably affected their developing brains, increasing their disposition towards aggressive behaviour while growing up. .
Studies have found that testosterone can also influence the brain in a similar way. As a predominantly male sex hormone, linked in animal studies directly to aggressive tendencies (Goy), extensive research has been carried out in order to discover if this link extends to males and females. Dabbs, Carr, Frady and Riad (1995) studied this issue concerning male and female inmates. Among the males, it was found that those crimes involving violence showed higher testosterone levels than non violent crimes, and it was more probable that prisoners with higher testosterone levels would commit rule violations and physical confrontations.