Male aggression is natural

A team from the Department of Biology, University of Akron, has found that male rat aggression results from reduced levels of serotonin in the brain.

The researchers suggest that aggressiveness in human males is also the result of reduced levels of seratonin in the brain and is not a learned behaviour.

The research was conducted on a colony of rats. By introducing new male and female rats to an established colony, the researchers could observe the resulting behaviour. The males in the group reacted strongly to introduced male rats. The intruders were attacked on average 2.6 times, sustaining 1.8 wounds over a 15-minute period. Females in the colony did not show any aggression towards any of the introduced rats.

After the experiment, norepinephrine, dopamine and serotonin were measured in various regions of the brains. Serotonin is one of several substances known to affect mood and aggression. The decreased serotonin in the male brain was associated with increases in aggressive behaviour.

It turns out that levels of dopamine and serotonin were less in the male rats than the female rats, but norepinephrine levels were not statistically different between the male and female rats. The Y chromosome governs serotonin levels. The researchers conclude that when the Y chromosome is stimulated, serotonin levels decrease and testosterone increases. The result is aggressive behaviour.