Last updated August 15, 2018 at 11:06 am
Modelling suggests differences between the sexes aren’t the answer.
When two tribes go to war it’s usually only men doing the fighting, and that has been the case across the centuries, irrespective of how and how much warfare might have changed.
There are a number of possible contributing factors, but none really explains how infrequently women are involved in any number. In some cases, you would think, sheer weight of numbers might be an advantage.
Researchers from a range of disciplinary backgrounds have considered the question in recent years, and now three biologists from Scotland have taken a mathematical approach.
Alberto Micheletti, Graeme Ruxton and Andy Gardner from the University of St Andrews developed a model to assess the three most common hypotheses: that men might be predisposed to warfare because they are better at it; that the net cost of warfare may be lower for men than women; and that women may be relatively less incentivised to participate owing to female-biased dispersal being associated with their having lower kinship to those group mates who stand to benefit in the event of success in warfare.
It comes down to evolution
Their conclusion? It might ultimately come down to the fact that, when it comes to evolution, men compete with men and women with women. This means, they suggest, that it takes only a small trigger, like male aggression when competing for women, for more men to initially go to war.
Once the balance is tipped, competition also makes it more likely for the bias to continue. Greater strength and effectiveness in battle, together with other sex 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,” they write in a paper published in 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.”
This is not the first time the trio has applied mathematics to study of warfare. Last year it reported, also in Proceedings of the Royal Society B, on a study looking at intrafamily and intragenomic conflicts, including the interplay between sex-specific demography and human warfare.