woman, fighter, France

In the new study “Why War is A Man’s Game” biology researchers from the University of St. Andrews seek to explain why battles have predominantly been just that — a conflict between men. Warfare, they claim, is essentially and exclusively conducted between men, even though women, representing half the population, “fail to participate in battle.” The researchers argue that the reason why men fight and women don’t isn’t necessarily because of sex differences in attitudes or abilities, but because of chance.

These findings are based on a mathematical analysis designed to determine how male and female participation in war can evolve over time. The researchers explain in the journal Proceedings of the Royal Society B that their model demonstrates that the more one sex participates in war, the less the other sex is inclined to do so. This inevitably and subsequently leads to only one sex fighting in battle.

“We found that participation in war by one sex alone evolved even in the absence of the sex differences, which are considered to be crucial in existing literature,” study co-author and postgraduate student Alberto Micheletti tells Inverse.

soldiers
Ancient Samnite soldiers represented on a 4th century B.C. tomb frieze.

While Micheletti and his co-authors emphasize that chance underlies all of this — had women been more aggressive at the start, they argue, maybe they would have been the warring sex — aspects of “sexual selection” are still a factor here. They reason that male versus male competition over opportunities for reproduction may have caused men to evolve to be naturally more aggressive, and this could have been the tipping point for their inclination towards war. War is a quick grab for resources and reproductive opportunities, so looking at this from a Darwinian perspective, it stands to reason that men have more to gain from war than women.

“They address a very interesting question, not simply the sex difference in physical aggression and engagement in war, but why it is an almost exclusively male endeavor, at least among people,” David Geary, Ph.D., a University of Missouri-Columbia professor and author of Male, Female: The Evolution of Human Sex Differences tells Inverse. Geary was not a part of this research.

Geary says that their “conclusion that the sex difference in engagement in war is related to men’s physical advantages, lower costs relative to women, especially when many men in their group participate, and the tendency of men to stay in their birth group in traditional contexts makes a lot of sense to men.”

What this study does not calculate in, however, is the factor that historically women have been barred entry into war.

“We did not consider the possibility that women might be actively barred from participating in warfare, as our goal was to understand how natural selection shapes incentives to participate in warfare,” says Geary.

But it remains true that for women in recent history the choice has not been as simple as do you want to go to war or not. The female warriors that are famous are so because they defied societal laws and standards and, often illegally, entered into warfare. In the Civil War, for example, it’s estimated that around 400 women disguised themselves in order to fight, even though they legally were not allowed to. Today 16 percent of the U.S. military consists of women, but it wasn’t until 2015 that they were allowed to serve in front-line ground combat positions.

Geary reasons that while modern culture may be “over-riding the biological basis for exclusively male warfare,” in turn influencing more women to join the military, ancestral behavior still has an effect on the number of women who are in the armed forces. That is difficult to prove scientifically. What’s also true is that the ethos underlying the armed forces has not made it easy for women to join.