About the logo
'War is to Man what Motherhood is to Woman?' Very good, I think you'll agree. A fine slogan with a lot of virility to it ..."
      The Duce, from Louis de Bernieres'
      Corelli's Mandolin
AFWW logo

Biological Differences Between Men and Women With Respect to Physical Aggression and Social Stability

(The following is excerpted from Shift: A Future Without War.i)

Martian Men and Venusian Women

Might we have any reason to think women could be biologically geared to react differently than men when it comes to war? Isn't it possible that if women had governing power in our societies, perhaps that seductive sway would lead them to act exactly like men, including the launching of wars?

John Gray wrote a popular and often cited relationship book, Men are from Mars. Women are from Venus.ii The book suggests how men and women can understand their differences in order to communicate better and get along. Some differences between men and women are superficial (changing fashion can quickly alter them—e.g. American men don't use hair dye) or the differences are cultural, not based heavily on genetics and thus changeable, although often not readily so (e.g., women don't fight on front lines in American wars). But this much copied phrase does express a significant kernel of biological truth. Some differences between men and women have deep genetic origins and are, for all practical considerations, unchangeable.

Evolutionary biologists have for years explored what they call male and female reproductive strategies. It is commonly the case across the animal kingdom that males can produce a great many sperm compared to females' more limited production of eggs. These fundamental biological differences create different priorities and pressures on the two sexes. The result produces differences in their behavior that are dramatic. They are often described as a “battle of the sexes.” With respect to war, understanding this principle is fundamental to understanding why as groups, men's and women's reactions to social conflicts differ.

The anthropologist Sarah Blaffer Hrdy wrote a broad survey on human reproductive behavior, Mother Nature: a History of Mothers, Infants, and Natural Selection.iii She focused on the priorities and pressures on women. One thing to note from the outset is that in Mother Nature Hrdy dismantles the idea that women are made of sugar and spice and everything nice, while men are less delightful, made from snips and snails and puppy dog tails. She makes clear that women are aggressive beings, that they create dominance hierarchies and defend them. And most remarkably, women under a variety of social and physical pressures will abandon or even kill their offspring, something almost never seen with other primate females.iv

Furthermore, cross-cultural studies reveal that men in many cultures care for children, and men who bond early with their children can be very nurturing. Barry Hewlett, for example, studied father-infant bonding in Aka pygmies and finds that fathers there bond with their children by regular hugging, kissing, and soothing care.”v

So we begin our exploration into gender differences and how these may relate to war by dismissing any idea that women are innately nicer or more nurturing than men…or for that matter, more moral. If in our search to understand our capacity for peace or war we find differences in how men and women use physical aggression and relate to war—and we will find differences—it won't be because women are sugar and spice and men aren't.

Mother Nature presents in detail a list of references as well as evidence that forms the backbone of the following biological logic. Deborah Blum's introduction to her book, Sex on the Brain provides another, brief discussion of most of these biological points.vi

The Biological Logic – Why Men and Women Respond Differently to Conflict

Keep in mind two biological facts: first, we are mammals because like all female mammals, our females produce milk to feed their offspring. And second, we're primates, related to chimpanzees, gorillas, and orangutans and more distantly to baboons and monkeys. Keeping these biological facts in mind, the biological logic goes like this:

  1. For all living things, the basic biological bottom line is to reproduce and have offspring that in turn have offspring. Genes of individuals that fail to reproduce are eliminated from the great evolutionary game of life. This means that the behavioral inclinations coded in those genes are not passed to subsequent generations. There are some subtleties here—for example, highly social animals (bees, humans) can often contribute some genes to the future by aiding close relatives who possess the same genes rather than reproducing themselves—but such subtleties don't alter the basic biological reality.

  2. For female mammals, and certainly for female primates, reproducing successfully is a very expensive proposition. Female primates carry an offspring to term, protecting and nourishing it within their body, often for many months. They must risk the hazards of childbirth. Then they provide milk to nourish it for weeks if not months or even years more. They must protect it, care for it, and support it sometimes for many additional years before it is old enough to reproduce. Women must bear, protect, and care for a child for a minimum of twelve to thirteen years before that child is capable of reproduction, and in bearing, giving birth to, and rearing offspring, women risk and invest far more than men do. For every parent raising children, whether in the United States, Brazil, Thailand, or Ghana, the extensive costs involved (in time, energy, risk, and resources) resonates deeply. And then, in most cultures, once a child is raised, females remain involved in ensuring that the offspring of their offspring—their grandchildren—also survive. For females, this is, beyond doubt or argument, an extraordinarily expensive process.

  3. Therefore, the ideal condition for female primates is social stability for long periods. Serious social turmoil, anything that threatens the life of these expensive offspring before they can reproduce is hugely counterproductive. What this has meant in women's evolutionary history is that any serious turmoil—which certainly includes a war that might result in the woman's death or the death of her children—has been highly counterproductive for our female primate ancestors. War for our female ancestors as well as for modern women is an extraordinarily dangerous threat to reproduction.

  4. For male mammals, including male primates, the biological game is usually quite different, because they do not invest as heavily in the survival of their children as females do. In some primates, fathers contribute nothing beyond their sperm. While human males often become involved in support and protection of their young, this isn't the case in all cultures (see, for example, the Mosuo described by Hua where technically there isn't even an institution of marriagevii). In few cultures does a father's investment approach that of a mother though there are some notable primate exceptions, tamarins for example. But compared to females, male mammals including male primates are generally more involved in spreading their seed widely than investing heavily in any given offspring. Should males loose offspring as a consequence of conflict or war, they can more easily sire replacement offspring than females can bear, give birth to, and raise replacements.

  5. Therefore, for many male primates, including men, social stability is not as high a priority as it is for females. In male-dominated cultures, for example, much of men's social lives centers around rearranging the social order in their dominance hierarchies to achieve greater social status.viii Joshua Goldstein's War and Gender provides a comprehensive review of the importance of forming dominance hierarchies by male primates, and that includes humans.ix Hrdy, in her book The Women that Never Evolved, defines dominance as “the ability of one individual to influence or coerce the behavior of others, usually by threatening to inflict damage but also by promising to give (or withhold) rewards.”x Sometimes this involves using physical violence. In humans, dominance does equate with status, and with the ability to control others. By extension, war is an expression of the inclination to control/dominate others carried out on a grand scale.

One possible biological explanation for this sex difference is the male primate urge to rise in rank. The rationale would be that when a male rises in rank within the group, he is able to mate with more females, thus spreading his seed as widely as possible.xi Joshua Goldstein, in War and Gender, reviewed data on the relationship between reproductive success and the obsession with dominance relationships in male primates. His analysis indicates that this hypothesis does not seem to be the explanation.xii Another hypothesis explaining this male urge for higher status is that it results in greater accesses to resources such as food or safe resting or sleeping sites.

It's possible, even probable, that higher status conveys different advantages in different situations. Whatever the reason, men today in the vast majority of cultures still compete regularly to overturn the social order. They seek to rise in rank if possible or to avoid losing status, and generally across cultures they are much more inclined than are women to use physical aggression to do so. Male groups, unless restrained by police or strong social prohibitions , or both, fight to dominate other male groups. The overall result of these different biological pressures and priorities is that social stability is not as high a priority for men as it is for women.

Other inherited traits also underlie our ability, and willingness, to wage war. One of these is an inclination for aggressive male bonding. Certainly for ancestors in our deep past it would have facilitated certain kinds of hunting, especially of large animals.

Goldstein provides a lengthy review of male bonding in humans as this relates to war.xiii He points out that small-group bonding is very important to combat effectiveness. Combat veterans will say that they fought, and if necessary killed in combat, in order to protect their comrades, not out of patriotism or hatred of the enemy. Military hierarchies attempt to extend this aggressive male bonding to the larger-unit scale with concept like “esprit de corps,” the idea of upholding group honor. Close-order drill is also used to create a sense of group cohesion.

Note that women display these same inclinations for status and bonding, only that in women they are not as consistently or strongly expressed; they are more characteristic of or take a stronger form in men in general. We see this tendency for aggressive male group action expressed in men's love of aggressive team sports, in young males that get together to do pranks, and when angry men form a mob— after a stolen election or simply after a soccer match. These mobs are very unlikely to be composed mostly of women.

Two other biological traits also facilitate the building of armies. One is an admirable trait, altruism in the form of willingness to defend or rescue other individuals of the group, even possibly at the risk of one's own life. There are many examples of humans doing this not only for family members but for members of their group, or for the group itself, which may not be composed of close relatives at all.

Goldstein describes another trait, the willingness to work in hierarchies, a characteristic of which is willingness to follow orders of members of higher rank.xiv John Horgan, in his book The End of War calls this trait “docility.”xv Goldstein, reviewing studies on primate hierarchies, says that as a general rule, “human males may be more hierarchical—oriented towards competition and status—whereas females are more empathetic, although with a 'great deal of plasticity' in gender roles.”xvi

From these books and similar works you can form your own assessment of the power of competition for resources such as food, territory, or access to females, to shape the evolution in many mammals, including many primates, of a male tendency to seek dominance status using physical force. In Shift I propose that while human males may have evolved often under an imperative to engage in dominance-seeking behavior that involves overturning the social order, a basic reproductive imperative for females has been to do whatever they can to foster social stability. Furthermore, that this female inclination to facilitate social stability is as deeply evolved in humans as the well-known and frequently discussed male inclination for dominance behavior involving group aggression.

This is why a world with fully empowered women sharing with men in decisions regarding war would be more socially stable: because of a female's unavoidable and costly commitment to her offspring, basic human female biological priorities are different from those of males.

These differences are not cultural. Their origins are deeply rooted in our evolutionary past. We inherit them from our pre-human primate ancestors. Given free rein and uncurbed by social or ecological forces, these opposed tendencies—with males ready to bond together in acts of aggression and females more inclined to seek social stability will— not only in the short run, but most especially over long periods of time—play themselves out in our group behavior. Not to take them into consideration when discussing the question of war and how to make a lasting peace is a profound error.


  • Hand, Judith L. 2012 In preparation.

  • Gray, John. 1992. Men are from Mars, women are from Venus: a practical guide for improving communication and getting what you want in your relationships. New York: Harper Collins.

  • Hrdy, Sarah Blaffer. 1999. Mother nature; a history of mothers, infants, and natural selection. New York: Pantheon Books.

  • Scheper-Hughes, Nancy. 2005. Lifeboat ethics: mother love and child death in northeast Brazil. In: Brettell, Caroline B. and Carolyn F. Sargent (eds). 2005. Gender in cross-cultural perspective. New Jersey: Prentice Hall.

  • Hewlett, Barry S. 2005. The cross-cultural nexus of Aka father-infant bonding. In: Brettell, Caroline B. and Carolyn F. Sargent (eds). 2005. Gender in cross-cultural perspective. New Jersey: Prentice Hall.

  • Blum, Deborah. 1997. Sex on the brain. The biological differences between men and women. NY: Viking Penguin.

  • Hua, Cai. 2001. A society without fathers or husbands: the Na of China. Translated by Asti Hustvedt. New York: Zone Books.

  • In egalitarian cultures this urge to rise in dominance is socially suppressed. Boehm, Christopher. 1999. Hierarchy in the forest. The evolution of egalitarian behavior. Cambridge, Mass.: Harvard Univ. Press.

  • Goldstein, Joshua S. 2001. War and gender. Cambridge, UK: Cambridge University Press. pp. 204-208.

  • Hrdy, Sarah Blaffer. 1981. The women that never evolved. Cambridge: Harvard University Press.

  • See for example Potts, Malcolm and Thomas Hayden. 2008. Sex and war. Dallas, TX: Benbella Books.

  • Goldstein, Joshua S. 2001. War and gender. Cambridge, UK: Cambridge University Press.

  • ibid. pp. 194-199.

  • ibid. pp. 203-210.

  • Horgan, John. 2012. The end of war. San Francisco, CA: McSweeney's Books. pp. 109-112.

Back to top