At the personal level.

Honour, glory, revenge -- these are what drove the ancient warrior cultures. Among the Masai of East Africa, North American Plains Indians, and scores of other groups, a man could not marry until he had proved his worth by killing someone in battle.

Many early societies loved war for its own sake. They thought that courage and skill in fighting were the noblest human virtues. The Scandinavian Norsemen were, perhaps, an extreme case. They imagined heaven as a place of eternal fighting, where wounds healed immediately and the dead rose at once to fight again.

The Aborigines of Australia went in for very formal affairs. They would give their enemies notice in a formal declaration of war. Battles would be fought at prearranged times and places. They would stop fighting by mutual agreement when they felt that honour had been satisfied.

Anthropologists put forward a number of reasons to explain why people -- usually men -- fight wars. Some say men, almost uniquely in the animal kingdom, possess some sort murderous instinct. Others say that materialism drives us to war: the need for slaves, more grazing land, or even human flesh to eat. Others point to the similarities between war and male pastimes such as hunting and outdoor sports -- these people suggest that it may be boredom that ultimately spurs men to fight. Still others say that war is Nature's way of ensuring that only the genes of the fittest and strongest are passed down to succeeding generations.

Recent research at the University of Pennsylvania suggests brain function may contribute to the male leanings toward war. Dr. Ruben Gur has found that the brains of men and women are identical except in the region that deals with emotional processing. The part controlling action-oriented responses seems to be more active in men than women, triggering them to fight. In women, however, the area of the brain thought to control more symbolic emotional responses is more active. As a result, women tend to react to an emotional stimulus with words, facial expressions, and gestures. Dr. Gur believes these differences are not just learned behaviour but have a physical basis.