Agustín Fuentes Ph.D.

Busting Myths About Human Nature

The Real Reason Sexual Violence Is So Widespread

An anthropologist challenges the idea that we're no better than animals.

Posted Jul 24, 2014

Aerogondo2 / Shutterstock
Source: Aerogondo2 / Shutterstock

It is believed by some — given those responsible for the recent violence perpetrated in today's news — that most rapists are men, most sexual harassers are men, and most incidents of domestic abuse resulting in injury are caused by men. Some would argue that men are naturally sexual predators.

But they are not.

The key word to focus on here is naturally.

When we hear the term "naturally,” we think of our biology and, thus, our evolution. If it is natural that men are particularly sexually aggressive, then it is easy to understand much of what goes on in our society. The ways our politicians talk about women’s rights and rape, the tragic shooting rampage of Elliot Rodger in Isla Vista, CA, the recent groundbreaking study of the frequency with which male scientists use power and hierarchy to sexually harass and assault junior, female scientists — all become understandable if they are simply reflections of what our evolutionary histories have shaped men to do. 

But they're not.

The arguments that evolution has made men particularly aggressive in regard to sex draw on comparisons with insects, seals, lions, deer, and our closest relatives, the chimpanzees, to justify assertions about the naturalness of sexual coercion and rape. Some also suggest that we can look at modern small-scale human societies — those where people live more like our ancient ancestors than most in the industrialized world do — and get insight into the evolutionary reasons for male aggression, sexual and otherwise.

These arguments are popular with many scientists and the public, because they make it easier for us to deal with male violence and aggression towards women — believing these assertions means that sexual violence, while undesirable, is a central part of human biology, and thus inevitable. 

This belief is both dangerous and wrong. Sexual violence is the fault of the perpetrators, not their genes.

Many of the arguments for the basis of sexual aggression in the animal kingdom are based on poor data or assumptions now known to be incorrect — or just ignoring data that do not fit with their model.  

This is dangerous, because sexual violence is a serious problem in many societies, but to accept that it is an inevitable part of being human takes away a degree of responsibility for how we act and how we expect our fellow humans to act.

Let me explain.

Biologists have long argued that basic sex differences related to reproduction evolutionarily favor sexually aggressive males. However, this basic assumption has been extensively challenged and is now realized to be a much more complex story. Reproduction is not just about the size of the sperm and egg, not just about who gestates and lactates — there is much more going on. Recent work undercuts the arguments for males not contributing much to reproduction, for males primarily using aggression to get females to mate with them, and for the concept that male and female humans are dramatically different when it comes to reproductive goals and behaviors. 

Sure, there are many species of insects, and some mammals, in which the males are very sexually aggressive — but there are also many in which they are not. Specific research on our closest relatives finds a wide range of patterns and behaviors for males and sex: Primates (and humans) live in complex societies with many ways for males and females to get along — some violent, many not. There is no smoking gun for male sexual aggression in the biology of humans or other animals.

But what about the specific argument that aggressive or coercive human males leave more offspring? If this were the case, one would see the evolution of sexual aggression as a core part of being human.   

But there are extremely few studies of humans that actually strive to test the question: Do aggressive males fare better? There is one famous study held up by many to support the assertion that male aggression is an evolved strategy, which is often used as the final word of “proof” on the matter: The Yanomamö are a small-scale society in South America whose people engage in relatively high rates of aggression and violence, sometimes resulting in death. If a Yanomamö man is involved in a killing, he must undergo a ritual in which he becomes a unokai. A minority (fewer than 30 percent) of men become unokai. It has been claimed that unokai have, on average, 2.5 more wives and three times the number of children as non-unokai. This difference is one of the most cited examples of an evolved relationship between aggression and reproductive success in human males.

However, while unokai do have, on average, more offspring, they are not being compared with a group of men who are the same age. Age affects dominance and reproductive success across the animal kingdom. Anthropologist Doug Fry's reanalysis of the original Yanomamö dataset shows that unokai are on average 10.4 years older than non-unokai. It is not surprising that, on average, men who are 10 years older have more wives and children (a common pattern in many societies). This changes the relationship between being a unokai and having more kids to one that includes age, not simply aggression.

Adding to this story are the data on the Waorani, another much-studied South American society known for its aggressiveness. Anthropologist Stephen Beckman and colleagues examined the genealogies of 121 Waorani elders and the complete histories of 85 warriors. They studied raiding histories, marital records, and the number of children per man and discovered that “more aggressive men, no matter how defined, do not acquire more wives than milder men, nor do they have more children, nor do their wives and children survive longer.” They also found that more aggressive men had fewer children who survived to have kids themselves.

It turns out that aggressive males do not “do better,” in an evolutionary sense, in either of the two well-known, well-studied examples of hyper-aggressive, small-scale societies where reproductive success was actually measured.

So if men are not naturally sexual predators, why does it happen so often? 

A full answer to this question is complicated, but here is a short one: There are a bunch of social, historical, and biological realities that make it more likely that males will resort to violence and coercion when it comes to matters of sex and conflict.

Males are, on average, larger and have greater upper-body strength than women, and thus are more capable of harming them in direct conflict than vice versa. Also, while male and female sexual arousal physiology is quite similar, there are massive differences in social expectations and learning environments that can radically increase differences in expectations, desires, and even brain function between males and females. The way we grow up shapes the way our minds and bodies respond.

In many societies, it is more acceptable for males to use violence to solve problems than women. Many historical, political, and even economic patterns create contexts in which men are assumed to have “rights” of access to females for sex — remember, it has not been that long since wives were considered the property of their husbands or, for that matter, since women got the right to vote. Even many religious traditions place male roles and male sexuality above those of females. Given the contexts in which our bodies and minds develop, it is no wonder that many boys and men in our society often accept that it is “natural” to be sexually coercive, even if just a little bit.

So when men’s rights groups bemoan the oppression of their “nature” by women, they are wrong. When anyone asserts that sexual coercion, harassment, or even rape is, at least in part, driven by biological prerogatives, they are wrong — and no one can use biology and evolution as an excuse for being a jerk. That does not mean that such behavior is not an ongoing reality — it just means that it is a reality that we can alter.

Most men aren’t sexual predators. But we need to be more active when someone is — especially with regard to sexual harassment, coercion, and assault on women. Society needs to own up to the fact that sexual aggression is not inevitable — but it is predictable, explicable, and, in most cases, avoidable.