Why Are Humans So Violent?

Are humans beings innately violent — and if so, have we always been that way? It's a question that has preoccupied scientists for a long time; psychologist and linguist Stephen Pinker, for instance, had a smash hit book on the subject with The Better Angels Of Our Nature, in which he argued that humans were becoming gradually less violent towards one another in the modern world. (It's a thesis that's been disputed a lot.) But when it comes to the idea of an inherent human tendency towards violence, a new study published in Nature posits that we may have a certain kind of predisposition towards it — because of our position in the evolutionary tree of mammals, and what that placement does to our behavior towards other members of our species.

However, this is not to say that violence is a "mammal thing": a large proportion of mammals are pretty peaceable towards one another, or at least haven't ever been observed beating each other up or committing murder. (That's an important distinction: there may be more violence in the mammal kingdom than we ever anticipated, which we are simply not aware of because it is done out of the sight of David Attenborough and curious scientists.)

Rather, what seems to be significant, according to the new research, is the fact that we're related to primates, and how our ancestors in the Paleolithic period stack up against other ancestral primate species. It seems that being a primate descendent gives us a certain, well, taste for blood. That baby chimpanzee video you've been watching all morning doesn't look so adorable now, does it?

Primate Violence Is Not Monkey Business

The story behind the research in Nature is one of relationships, and not just murderous ones: the ones between species, and how humans relate to other mammals ancestrally. The study, led by José María Gómez from the University of Granada, looked at human violence through an unprecedented lens: how records of it throughout history stack up to other mammalian species, both those we're related to and those very different from us. And the numbers are staggering: the scientific team looked at more than 4 million incidents of violence within a species (like cannibalism or murder) in 1,024 mammals. And they lined those up with 600 studies of human violence throughout history, from early history and the Paleolithic period to the modern day.

What they discovered was pretty astonishing. For starters, the researchers found that nearly 40 percent of mammals evidently use violence against one another (though they say this might be an underestimate: remember, murders sometimes go unnoticed and undocumented). But primates are particularly deadly; as National Geographic reported, "While only about 0.3 percent of all mammals die in conflict with members of their own species, that rate is sixfold higher, or about 2 percent, for primates."

Shockingly, meerkats commit the most interpersonal violence among all mammals — which is not how we humans generally think of the critters. More significantly, only 0.3 percent of deaths among all mammals are murders; but among primates, it's around 2.3 percent. So we're not as bad as meerkats, where 19.36 percent of recorded deaths were murders by their own kind (bloody hell) — but we're pretty in line with primate trends.

What does all this mean? Well, the scientists say, it creates the distinct possibility that "a certain level of lethal violence in humans arises from the occupation of a position within a particularly violent mammalian clade [group of descendants from one ancestor] in which violence seems to have been ancestrally present.” They think we get some of our particular rates of violence, or at least got them, from our primate ancestors. But does this mean we can start using genetic excuses for hitting people on the head?

Are We Destined To Be Violent Because Of Our Biology?

Animal behavior isn't the end of the story, though. The scientists also took in a lot of data about the massive shifts in human violence throughout history. While the Paleolithic human levels of violence fit their model predicting how violent different primate species should act, and the medieval era was one of the most lethal periods in human history for person-on-person death, levels of violence among humans have actually fluctuated a lot, including a large dip in the modern day. And that, the scientists say, means that we're not just destined by biology to be violent — society has a huge role to play in how we use our evolutionary strategies. Lead scientist Gomez told The Guardian that “lethal violence is part of our evolutionary history but not carved in stone in ‘our genes’. At least to some extent, the way humans organise in societies influences our levels of lethal violence.” In other words, while our genes may have taught us that violence is a good solution, the way in which we live heavily influences how we use that lesson.

There have been a few arguments about whether the data is precise enough to give us a nuanced look at human-based violence, though. One expert called the scientists' collection of species violence "a real soup of figures", because it included everything from cannibalism to infanticide to individual fights. This isn't a nitpicking response; defining kinds of violence matters, particularly because they tend to differ significantly between species and between primates. Biological anthropologist Richard Wrangham told National Geographic that one of the things that really distinguishes human violence is that it's largely done by adults to adults — the group of animals that engages in this kind of behavior is "very small," according to Wrangham, with lions and wolves as co-members. Among most primates, the most common form of murder is killing children. So the precise nature of our inheritance, and whether it's legitimate to say all kinds of violence have some kind of evolutionary component, remains unclear.

So what can you do with this information? It's helpful to know that some scientists think we've evolved to know violence might get us out of a tight spot. But it's also important to remember that society plays an enormous role in shaping our attitudes towards committing violent acts — so biology is no excuse. Meaning, there won't be any successful murder defenses based on "my primate brain made me do it" any time soon.

Image: Martin Fisch/Wikimedia Commons, Giphy