Gender roles in war play out by the numbers

The reason warfare is overwhelmingly conducted by men rather than women may lie in brute mathematics, researchers say.

The reality of gender roles in warfare is stark and ancient. With few exceptions, armies are primarily male, even though – as some of those exceptions amply demonstrate – women are just as capable of fighting.

Attempts to account for this phenomenon have cited many different potential causes, from the existence of violent male rituals to the influence of gender-biased written and visual fiction.

Now, however, three biologists from Scotland in the UK have taken a mathematical approach. Alberto Micheletti, Graeme Ruxton and Andy Gardner from the University of St Andrews developed a model to assess and compare the three most common hypotheses.

These are that men are predisposed to warfare because they are better at it than women; that the net cost of warfare may be lower for men; and that women may be relatively less willing to participate because female dispersal through marriage means they have less kinship to group-mates who stand to benefit in the event of success in warfare.

The researchers conclude that it all might ultimately come down to the simple evolution-driven fact that men compete with men and women compete with women. This means, they suggest, that it takes only a small trigger, such male aggression when competing for a mate, for more men to start fighting.

Once the balance is tipped, male-to-male competition also makes it more likely that the gender bias will continue. Greater strength and effectiveness in battle, together with other gender differences, may have also reinforced this pattern.

“Surprisingly, we find that exclusively male warfare may evolve even in the absence of any … sex differences, though sex biases in these parameters can make this evolutionary outcome more likely,” Micheletti and colleagues write in a paper published in the journal Proceedings of the Royal Society B.

“The qualitative observation that participation in warfare is almost exclusive to one sex is ultimately explained by the fundamentally sex-specific nature of Darwinian competition – in fitness terms, men compete with men and women with women.

“These results reveal a potentially key role for ancestral conditions in shaping our species’ patterns of sexual division of labour and violence-related adaptations and behavioural disorders.”