Societies, Not Genetics, Turn Us Into Killers

You don’t need to look much further than your newsfeed for evidence that human-on-human violence is common. But do all those screaming headlines — and victims — prove we’re born to kill? A new study of violent behavior across the evolutionary tree, published Wednesday in the journal Nature, reports that we and our great ape relatives are more murderous than the average mammal, but goes on to conclude that there is not a genetic basis for that killer flaw.

The study was carried out by a team of scientists at the University of Granada in Spain attempting to figure out whether certain species were more prone to violence. To do so, they looked at the incidence of “conspecific” violence — that is, animals killing their own kind — across 1,024 types of mammals. Sure enough, some interesting insights into our species emerged: At the dawn of Homo sapiens, the incidence of human-on-human violence was about six times higher than it was for the average mammal, but it was pretty much on par with what was expected for a species within the great ape family.

Humans weren’t the most murderous species — not by a long shot. That morbid title went to the meerkats, a species in which about 20 percent of deaths happen in the first degree. By contrast, when Homo sapiens arose, only 2 percent of deaths in our species were murders.

A murder rate of 1 in 50 humans, of course, is still alarmingly Hobbesian. But that’s not the big takeaway here. By showing that certain groups of species — like the great apes, the murderous meerkats, and, uh, lemurs — tend to have similar incidences of conspecific violence, this research suggests that there is an underlying reason for this anti-social behavior that isn’t genetic and doesn’t speak to “human nature.”

“We cannot tell that 2% of violence is due to genetic factors,” José Mara Gómez, Ph.D., the first author of the study, told the Guardian. “Not only genes are inherited from ancestors, also environmental conditions and ecological constraints. Those are also probably influencing the human lethal violence in our evolutionary past.”

The fact that the lethal violence level of two percent didn’t stay fixed over the course of our existence is evidence that other factors are at play. The way we organize our societies is a big one: As the study points out, our murderousness has fluctuated, spiking during the rise of prehistoric man, the Iron Age, and the Post-Classic age. These periods correlate with our preference for certain types of socio-political organizations: Humans were more murderous when tribes and chiefdoms were the preferred social structures, and less so when hunter-gatherer communities were popular. (For what it’s worth, our tendency to kill each other is currently at an all-time low.)

It’ll be interesting to see what great ape experts make of the data; our chimp, gorilla, and bonobo cousins, after all, haven’t changed their social structures much over the course of their existence, so they might provide a clearer view of how much of a role genes actually play in driving lethal violence.

For now, there’s one key takeaway: Whether or not murderous behavior has a genetic basis, history has shown that we can curb it. Whether we will, for better for worse, is also in our hands.