The Chronicle of Higher Education
From the issue dated May 24, 2002

Evolution, Males, and Violence


[Topic sentences are in green. Ask if the topic sentence could not, in many cases, be moved to the start of the paragraph. Howver the first paragraph is good example of issue sentences introducing the main point of the article as the end of the paragraph.]

Imagine that you were interviewing an intelligent fish, and you asked it to describe its environment. One thing it probably would not volunteer is that things are awfully wet down here. Like our hypothetical interlocutor, people are generally insensitive to whatever permeates their lives. So, if you were to ask someone to describe human violence, only rarely would you hear that it is overwhelmingly perpetrated by males. And yet, the truth is that if we could eliminate or even significantly reduce male violence, we would pretty much get rid of violence altogether. The maleness of violence is so overwhelming that it is rarely even noticed; it is the ocean in which we swim.

What might be called the "killing establishment" -- soldiers, executioners, hunters, even slaughterhouse workers -- is overwhelmingly male. Underworld killers such as violent gangs are also peopled largely by men. Whenever seemingly unprovoked and deadly shootings occur in homes and workplaces, men are typically the mass murderers. Nor is this imbalance limited to the United States: Whether in Kosovo, Rwanda, Cambodia, the Middle East, Guatemala, or Afghanistan, when people kill and maim other people, men are nearly always the culprits. And of course, the lethal operatives of Al Qaeda and its equivalent are reliably male, as are those sent to combat them.

The same gender imbalance applies to the uncountable private episodes of violence that receive little national attention but are the stuff of many a personal tragedy. Admittedly, an occasional Lizzie Borden surfaces, but for every Bonnie, there are about a hundred Clydes. Male brutalizers and killers are so common, they barely make the local news, whereas their female counterparts achieve a kind of fame. A man who kills -- even his own children -- gets comparatively little notice, whereas when Susan Smith drowned her two sons, in 1994, she received international attention. Violence may or may not be as American as cherry pie, but it is as male as can be.

Violence is also, by and large, something that men direct at other men. As with inner-city crime, in which both the perpetrators and victims are disproportionately members of minority groups, men are disproportionately both the perpetrators and victims of their own violence. This is not intended to romanticize or idealize women, or to deny that they too can sometimes be nasty, brutal, even deadly. Some women are more violent than some men, just as some women are taller, stronger, or have deeper voices or less hair than some men. But the overall pattern is consistent: When it comes to violence, the two sexes simply are not in the same league.

The same pattern is found, by and large, in animals.

Until a decade or two ago, it appeared that other animals -- including monkeys -- did not kill members of their own species, whereas humans did. But as field studies in animal behavior have become more thorough, the myth of the peaceful primate -- or non-murderous animal generally -- has largely been dispelled. Orangutans rape, for instance, and chimpanzees murder. Wolves also kill others of their own kind, as do lions, elk, and bison. In fact, nearly every animal species that has been carefully studied sooner or later reveals its penchant for lethal violence. And, to repeat, when such things take place among animals, the perpetrators are almost always males.

Why is this? Evolutionary biology has an answer, and it emanates directly from the very definition of male and female.

Just look at the exterior genitals of a bird. In nearly every species, there aren't any. Males and females simply have a cloaca, the common external opening for excretory and reproductive products. And yet, biologists have no difficulty distinguishing male birds from females; ditto for males and females throughout the natural world. The difference between the sexes has nothing to do with penises or vaginas, beards or breasts. Rather, it is a matter of gametes: the tiny sex cells identifiable as either eggs (if large and produced in small numbers) or sperm (if small and produced in large numbers). This and only this is the meaning of maleness and femaleness: Sperm makers are called males, egg makers females.

The consequences of that distinction are weighty indeed. In brief, since sperm can be made in vast quantities, and with little mandated physiological follow-through, it is possible for males to have large numbers of offspring, the actual output limited by the number of females they succeed in fertilizing. By contrast, females are more likely to maximize their reproduction by producing successful offspring, rather than by outcompeting other females for the sexual attention of males.

To some degree, sexual competition is a replay of fertilization itself, in which numerous males, like hyperactive spermatozoa, compete among themselves for access to females. Just as it is now clear that the egg doesn't merely passively receive suitors, it is increasingly understood that females can be active participants in their own reproduction. Nonetheless, when it comes to sperm makers, success is likely to crown those who outcompete their rivals, and so, in species after species, it is the males who are larger, nastier, more likely to be armed with lethal weaponry and a violent disposition to match. Natural selection has outfitted males with the tools for success in male-male competition, much of it violent.

In the animal world, human no less than nonhuman, competition is often intense. Males typically threaten, bluff, and if necessary fight one another in their efforts to obtain access to females. Among vertebrates in particular, males tend to be relatively large, conspicuous in color and behavior, and endowed with intimidating weapons (tusks, fangs, claws, antlers, etc.) and a willingness to employ them, largely because such traits were rewarded, over evolutionary time, with enhanced reproductive success.

Male-male competition is especially fierce in polygynous, harem-keeping species such as elk, moose, elephant seals, and gorillas. Whereas in such cases each egg maker is likely to be modestly successful (with one pregnancy per year), males play for higher stakes. They end up as harem masters or as evolutionary failures, and not surprisingly, they grow up large, tough, and well-armed: unpleasant bullies, as befits a winner-take-all lifestyle.

Consider elephant seals, behemoths that congregate annually to breed on islands off the coast of California. They are highly polygynous, with successful harem keepers fathering some 40 offspring per year. And not surprisingly, the male elephant seal is truly elephantine, outweighing the female fourfold; he is also strongly disposed to violence, nearly all of it directed at other males. Why? Because among his ancestors, success has been rewarded -- 40 times per year.

At the same time, since the sex ratio is one to one, for every harem master, there are 39 disappointed bachelors. As a result, some males will be immensely successful and others will be failures. By contrast, the difference between success and failure is much less extreme among females. Think of it as different degrees of reproductive democracy, or egalitarianism. The payoffs for females are more equitable than for males: one female, one offspring. Males, by contrast, operate in a system that is more inherently unfair and unequal. For them, there is a greater difference between the reproductive "haves" and "have-nots." Hence, males are much more competitive than females.

In species that are monogamous or nearly so -- such as most songbirds, geese, eagles, foxes, and gibbons -- males and females produce approximately equal numbers of offspring. Not surprisingly, in such cases the two sexes are also nearly equal in size, armament, and aggressiveness. As we come to species that are more polygynous, however, we find a steady progression toward greater inequality in size and aggressiveness, with males getting bigger, and more nasty to each other. Among polygynous primates, for example, we find noticeable size differences between male and female, and also marked differences in behavior, especially when it comes to violence. A similar pattern holds for the deer family, the seals and their relatives, and indeed, pretty much any animal group that is diverse enough to permit comparisons of this sort. In addition, the greater the difference in reproductive payoff (variance in numbers of offspring), the greater the difference in aggressiveness among males. With reproductive success more variable, males are more competitive.

This is not to deny recent findings that animals -- even males -- often cooperate. My point is simply that because of the basic biology of maleness and femaleness, of sperm and eggs, males are more prone to violence. Incidentally, it has long been thought that the sperm/egg dichotomy also generates profound male/female differences in sexual proclivities. Even though recent DNA studies have revealed that females are more prone to sexual adventuring than had previously been thought, when it comes to violence, the male/female divide is as robust as ever.

As to basic reproductive biology, human beings are pretty ordinary mammals. Homo sapiens is also typically mammalian in its predisposition to polygyny (a mating system in which a successful male mates with numerous females); thus, our situation is consistent with that of elephant seals, although less extreme. Of 849 societies examined in the anthropologist George P. Murdock's classic Ethnographic Atlas, 709 were polygynous, 136 were monogamous, and only 4 were polyandrous.

Time and again, and regardless of the methodology used to obtain their samples, anthropologists have come up with similar results: Before the cultural homogenization that came with Judeo-Christian colonial (and marital) doctrine, polygyny was the preferred marital system for more than 80 percent of human societies. (At the same time, even in non-Western, traditional cultures, most men did not actually succeed in becoming polygynists; monogamy, however, was nearly always imposed by necessity -- usually poverty, personal inadequacy, or a shortage of potential mates -- not choice.)

A Martian zoologist, reporting on the species Homo sapiens, would have no doubt: Human beings are mildly polygynous by nature. Like other polygynous mammals, we exhibit all the hallmarks.

Larger size and heightened aggressiveness were likely to lead to more surviving children, especially in the long evolutionary childhood of the human species. As to age at sexual maturation, individuals of the more competitive sex nearly always mature later, thereby avoiding violent competition when their youth makes it adaptive for them to leave the breeding (and the serious fighting) to the older guys. Finally, the sex experiencing greater competition typically suffers higher mortality as a result. When those characteristics appear in other species, biologists readily interpret them as indicating male competition for access to females. Combined with the overwhelming cross-cultural data on Homo sapiens, we can safely conclude that in their history, human beings were polygynous. In their biology, they still are.

Hans Morgenthau, one of the great figures in 20th-century political science, used to argue that politics was based on male competition for power, a contest that was, in turn, driven by three urges: to live, to propagate, and to dominate. Correct as far as he went, Professor Morgenthau might have been interested to learn that the first and third urges he identified are themselves proximate means to the middle one, the one that counts biologically: propagation. Reproduction, after all, lies at the root of why living things live, and why they seek to dominate. The ultimate power of propagation explains why males in particular are often so eager to dominate, occasionally carrying their eagerness to violent extremes. We should not be surprised to find that aggressiveness is widely -- and all too correctly -- seen as manly and its alternative, timidity, as womanly.

This is not to claim that females aren't aggressive in their own way. There are interesting cases of vigorous female-female competition in animals: Among groove-billed anis (large, ravenlike neotropical birds), several females deposit eggs in a communal nest, and the dominant female is especially likely to evict the eggs of subordinates; dominant female African hunting dogs may kill the offspring of lower-ranking females; female red howler monkeys push around other females. In fact, many cases of monogamy among mammals may actually be enforced by subtle aggression by females toward other females. I predict, in fact, that further research will reveal that female-female competition among animals is more widespread than currently recognized. There is no doubt, however, that it is typically less direct, less boisterous, and much less violent than male-male competition.

On the domestic front, violent crime is overwhelmingly male. Studies of prosecution and imprisonment records in Europe, going back several centuries, as well as examinations of modern crime statistics from the United States and around the world show that men consistently outstrip women in criminality by a ratio of at least three or four to one. When it comes to violent crimes, the difference is even greater, with the disparity increasing as the violence intensifies (simple assault versus assault and battery versus manslaughter versus homicide). The only areas, in fact, in which women commit more crimes than men are prostitution (which some would argue is not a crime but an act between consenting adults) and shoplifting.

Another difference is that when women are consistently aggressive, it tends to take a defensive form, as when a woman kills a man who has abused her or her children, or fights to have a murderer condemned to death. The same is true among animals as well. A mother bear with cubs, for example, is notoriously fierce, as are other females who defend their young. Thus, while the aggression of women tends to be reactive, men are more likely to initiate violence, to commit truly "offensive" acts.

When it comes to the most serious violent crime, homicide, men are far and away the most frequent perpetrators. They are also most likely to be the victims, precisely as evolutionary theory predicts. Thus, murder is largely a crime of men against other men, a pattern that, in itself, points an accusing finger at male-male competition. For their book Homicide, two Canadian psychology professors, Martin Daly and Margo Wilson, reviewed murder records, specifically looking at cases involving members of the same sex, over a wide historical range and from around the world. They concluded, "The difference between the sexes is immense, and it is universal. There is no known human society in which the level of lethal violence among women even begins to approach that among men."

Daly and Wilson found that a man is about 20 times more likely to be killed by another man than a woman is by another woman. That holds true for societies as different from one another as modern-day urban America (Philadelphia, Detroit, and Chicago), rural Brazil, and traditional-village India, Congo, and Uganda. This is not to say that the actual murder rates are the same in those different places. In Iceland, for example, 0.5 homicides occur per million people per year, whereas in most of Europe, the figure is closer to 10 murders per million per year, and in the United States, over 100. The crucial point is that despite those wide differences, the basic male-female pattern remains stable: Male-male homicide exceeds its female-female counterpart by a whopping margin. That the ratio of male-male to female-female violence remains remarkably unvarying from place to place argues for its biological underpinnings and parallels the male-male competition seen in other species.

The same trend can be found across history. Thus, even though a 13th-century Englishman was 20 times more likely to be murdered than an Englishman is today, he was 20 times more likely to be murdered by another man than an Englishwoman was by another woman.

While in recent years women have been increasingly involved in crime, Daly and Wilson cite FBI statistics attributing the increase to growing numbers of women arrested for "larceny-theft." In contrast, the proportion of women arrested for violent crimes -- and for homicide, in particular -- has actually declined slightly.

In 1958, the sociologist Marvin Wolfgang published what has remained the classic study of homicide in America, based on nearly 600 murders in Philadelphia. Trying to explain why more than 95 percent of the killers were men, Wolfgang -- a proponent of social-learning theory and cultural explanations -- wrote, "In our culture the average female is ... less given to or expected to engage in physical violence than the male." We are supposed to infer that things are different in other cultures, but that simply is not so.

There is a powerful bias in the United States, promoted by most contemporary psychologists, anthropologists, and sociologists, that male-female differences have been created solely by differences in upbringing and social expectations. As a result -- whether by error or pre-existing bias -- social scientists have contributed to the vast myth of the equipotential human being, the idea that everyone is equally inclined to behave in any way. Equipotentiality is an appealing sentiment, attractively egalitarian. There is only one problem: It isn't true. Quite simply, it flies in the face of everything known about the biological underpinnings of behavior, and of life itself.

Moreover, if male-female differences derived essentially from arbitrary cultural traditions -- the well-known phenomenon in which societies typically imbue young men with the expectation of greater violence -- there should be at least some in which the situation is reversed, where young women are socialized to be the more violent sex.

Violence is often seen as primitive or immature. And yet, the reality is that even in this era of gun-toting 12-year-olds, murderous violence is distressingly mature: Overwhelmingly, it is adult behavior. It is also easily triggered. When Marvin Wolfgang conducted extensive interviews with convicted killers in Philadelphia, he was able to identify 12 categories of motive. Far and away the largest, accounting for fully 37 percent of all murders, was what he designated "altercation of relatively trivial origin; insult, curse, jostling, etc." In such cases, people got into an argument at a bar over a sporting event, who paid for a drink, an off-hand remark, or a hastily uttered insult.

To die over something so inconsequential as a casual comment or a dispute about some distant event seems the height of irony and caprice. But in a sense, disputes of that sort are not trivial, for they reflect the evolutionary past, when personal altercations were the stuff upon which prestige and social success -- leading ultimately to biological success -- were based. It is not surprising, therefore, that young men today will fight and die over who said what to whom, whose prestige has been challenged, and so forth.

Within a group subject to discrimination, the pressures and pains -- as well as the tendency to "act out" -- will be especially strong. Another way to look at it: The fewer the opportunities for social success, the greater the risks worth taking. From an evolutionary perspective, therefore, it is not surprising that young men, especially those from disadvantaged social and ethnic groups, are overrepresented among drug addicts, violent criminals, prisoners, and death-row inmates. And that angry and alienated men make up the overwhelming majority of violent terrorists.

Others have tried to explain the high rate of male violence without regard to biology. For example, advocates of social-learning theory point out that men -- whether African-American, Caucasian, Asian, or whatever -- are expected to be aggressive; women are supposed to be passive. So people grow up that way, it is claimed, meeting the expectations that society imposes on them. But why should society have such expectations? And why are those expectations virtually the same in every society around the world? And why do both men and women find it so easy to comply?

The British psychologist Anne Campbell, an advocate of social learning and cultural influence, thinks that men are more aggressive than women because men and women interpret aggression differently: Women see it as a loss of self-control and are ashamed of their anger, associating it with being pushy, nasty, and socially isolated. Men, by contrast, see their aggressiveness in a positive light, as a way of gaining control. To men, anger and even rage can mean courage, success, and triumph. Campbell's analysis is probably correct as far as it goes. But why do males associate aggression with success? And why do they view controlling others as more important than controlling themselves? Also, why do women feel so threatened by isolation and anything that smacks of diminished intimacy, while men feel threatened by anything that smacks of diminished prestige and authority? If the "answer" is that women are taught to react as they do, then I must repeat: Why are virtually identical patterns found in every culture on earth? And why are similar patterns even found in the most different "cultures" of all, those of other species?

All of the above is not meant to imply that biology is the sole explanation for the gender gap in human violence. We cannot do a thing about our evolutionary bequeathal; hence, we had better do all we can to ameliorate those conditions that predispose people to violence. And let's face it: Biology does in fact explain a whole lot, such that if we are going to intervene effectively, we would be well advised to understand the nature of our own predispositions. Just like the fictitious fish with which this essay began, it is time for all of us to look around and acknowledge that when it comes to the social construction of sex differences in violence, the traditional view is all wet.

David P. Barash is a professor of psychology at the University of Washington at Seattle and a frequent contributor to The Chronicle. His most recent book -- co-written with Judith Eve Lipton -- is Gender Gap: The Biology of Male-Female Differences (Transaction Publishers, 2002).

Copyright 2002 by The Chronicle of Higher Education
May 24, 2002 Section: The Chronicle Review
Page: B7