If you entitle your talk Sex and War, it’s bound to draw a good crowd, as was the case last Wednesday when more than 100 people showed up for a talk on the evolution of war at the Woodrow Wilson International Center for Scholars in Washington, DC. The speaker was human reproductive biologist Malcolm Potts of the University of California, Berkeley, who has just co-authored a new book called Sex and War. The premise of his talk and book is that men have a genetic predisposition to band together in groups to wage battle-- something known as team aggression. That may seem obvious to any football fan or soldier. But what’s less obvious is that while men have evolved to be more aggressive in this way, women have not: Potts could not find a single case where women banded together in a gang or group to attack other humans. Women murder, commit violent crimes, join armies and even become terrorists. But they don’t initiate or form groups for the purpose of murdering another member of their own species, as do males in street gangs or terrorist groups, says Potts.
In fact, no other animals, with the exception of chimpanzees, hyenas and wolves, are known to form groups of males that attack and kill members of their own species, says Potts. After analyzing data on aggression from studies of primate and human behavior, fossils and archaeology, Potts thinks that human males inherited their Stone Age yen for battle from ancient ancestors, perhaps even a common ancestor they shared with chimpanzees. Male chimpanzees have been observed forming groups of males that purposefully invade another group’s terrain and brutally kill solitary chimpanzees they encounter.
Since that time more than 5 million years ago, human males have gotten better and better at being aggressive team killers because males who wage battle on neighboring groups have an evolutionary advantage. When they invade new terrain, they gain access to new supplies of food and women, hence spreading their genes far and wide. Call it the Ghenghis Khan effect, but men who win battles, get more chances to mate. This also may be true today even where men don’t engage in real battles: Potts cited a recent study that found that men who had more of the hormone testosterone in their blood at breakfast took greater investment risks and made more money that day—and women clearly prefer rich, powerful men. He also argues that these Stone Age impulses cause male leaders to respond aggressively when attacked, as in the case of the 911 terrorist attacks. Male leaders initiated a “war on terror” rather than pursuing more diplomatic methods to prevent terrorism that might have been more productive, says Potts.
Potts argues that this trend toward team aggression is obvious in the fossil and archaeological records. Although the first evidence of warfare doesn’t emerge until 5000 to 8000 years ago with the first city-states, in the Fertile Crescent, there is evidence of extreme human aggression in the fossil record where cannibalism appears at least 800,000 years ago. Once humans begin waging war, they battle each other all over the globe, culminating in 21st Century terrorism and wars.
But what was good for males wasn’t necessarily a bonus for females. Women don’t gain anything when a few men gain access to more women—war just redistributes food and women still have the same number of babies, just fathered by fewer men. Women invest so much more time traditionally in growing, nursing and caring for their offspring, that they do better in peaceful times. And this has led to a battle of the sexes, says Potts. Men can continue to wage war if they dominate women. But when women get power it puts a damper on males’ aggressive behavior. Take the case of bonobo chimpanzees where females form strong alliances, which allow them to keep aggressive males in check. And less aggressive males that help provision females and their young, for example, get more chances to mate, so there is no evolutionary advantage for forming aggressive bands of males. That example, says Potts, suggests that if more women were leaders of nations, there would be less war.