Biology Does Not Make Men More Aggressive Than Women

by David Adams

in Of Mice and Women: Aspects of Female Aggression K. Bjorkvist and P. Niemla (eds.), Academic Press, Inc. 1992, Pages 17-25

Introduction

In 1988, the International Society for Research on Aggression formally endorsed the Seville Statement on Violence, four years after the workshops hosted by Dr. Kirsti Lagerspetz and her colleagues in Turku devoted to its planning. In a brief but important paper circulated at Seville, entitled "Are Wars Caused by Aggression?" she presented the following conclusion:

In sum, to account for war on the collective level by psychological motives and characteristics on the individual level, it is not sufficient or pertinent to mention only aggression as an explanation. ...we have mentioned fear, suggestibility, obedience, sociability, altruism, dutifulness, ambition, self-assertiveness, intelligence, language, fear of disapproval, desire for gain, search for security (fear of unemployment) and some other characteristics. Collective behavior never results from one type of motive only on the individual level.(1)

One will find almost this exact language in Proposition Five of the Seville statement, since the Lagerspetz paper was specifically used in drafting it.

The results of the work at Seville are well known. The Statement on Violence has been endorsed and disseminated by scientific and cultural organizations around the world (including UNESCO), and used effectively to counteract the myth that warfare is an inevitable result of human biology (Adams, 1989). It can be said that it prepares the ground for the construction of a vision of world peace.

In this article, I shall address an issue discussed at Seville, but not incorporated into the final Statement, by my recollection, because there was considerable controversy about it; there seemed to be no way to reach a rapid consensus, and we only had a few days to do all the necessary work. The issue concerns the obvious fact that men, not women, fight wars, and whether this fact reflects biological or cultural causes.

(1) The Lagerspetz paper circulated to the Seville signatories in preparation for their work was a draft provided at the Acapulco meetings of the International Congress of Psychological Sciences in 1984. Lagerspetz later expanded it into the paper cited in the references.

A politically Useful Myth A. THE MYTH

It is politically useful for some to argue that male monopolization of warfare is evidence that war is a product of biology. For example, in a recent review criticizing the Seville Statement on Violence (Somit, 1990), the reviewer says that,

1 Practically everyone who has studied this problem argues that, among mammals, the males are far more prone to aggressive behavior than females.

The author footnotes his remark by referencing two well-known scientific experts on aggressive behavior who have, indeed, made this claim. The claim is then used to argue against the Seville Statement by saying that Statement ignores what "practically everyone" knows.

No one disputes the fact that warfare is usually planned and carried out by men rather than by women, and that this is a very old tradition. According to Murdock's cross-cultural work, warfare is one of the few occupations which is almost exclusively done by one gender and not the other (Murdock, 1937). The only other occupations which are so gender specific are metalworking, hunting, and manufacture of weapons (all by men). I argue that hunting and metalworking are monopolized by men as adjuncts to their monopolization of war, because they also involve the use and making of weapons.

What is disputed, and what I will try to show is a myth, is the proposition that male mammals are more aggressive than females and that such a "fact" is relevant to the monopolization of warfare by human males.

B. REFUTING THE MYTH

To refute the myth, it is necessary to refute the assumptions on which it is based:

(1) that the gender differences in human institutional aggression (i.e., war) are causally related to gender differences in individual human aggressiveness;

(2) that human individual aggressive behavior is homologous to that of other animals;

(3) that among other animals, males are generally more aggressive than females.

In this article, I present evidence to show that both the first and third assumptions are false. The second assumption is probably true, but without the others cannot support the myth.

Institutional Is Different from Individual Behavior

Underlying the Seville Statement on Violence is the assumption that institutional behavior is quite different from individual behavior. This assumption is contained in the Lagerspetz conclusion; "Collective behavior never results from one type of motive only on the individual level." The confusing of institutional and individual behavior is a common error among people who argue that human behavior is biologically determined. A particularly good treatment of this problem may be found in the recent book by Seville signatories Jo Groebel and Robert Hinde concerning the issues raised at Seville (Groebel & Hinde, 1989).

I have presented evidence elsewhere to show that the remarkable gender specificity of warfare is due to institutional considerations that are only remotely related to biology (Adams, 1983a). To put the argument most simply, male monopolization of warfare arose to resolve a contradiction between the institution of marriage and the institution of warfare. In cultures with patrilocal marital residency and internal warfare, such as probably prevailed in prehistoric times, there is a potential conflict of interest for a woman warrior: should she take sides with her husband and his relatives on one side of the war, or support her fathers and brothers on the other? Under such conditions, every married woman becomes a potential traitor to her husband's side. Male

2 monopolization of warfare was probably instituted in order to protect male warriors against betrayal by their wives and to resolve the conflict of interest of the women themselves.

Evidence supports this hypothesis. Cultures in which no conflict of interest would be expected to arise, those with matrilocal marital residency or exclusively external warfare, have permitted women warriors in a number of cases. On the other hand, in none of the cultures surveyed have women warriors been permitted in societies where such a conflict of interest could arise.

One must assume that in the earliest societies, when war and marriage first arose, there would have been a tendency (not a monopolization) for more male than female warriors. Such a tendency can be easily explained by the obvious fact that a woman who is several months pregnant or nursing a baby cannot go on the long marches which war often requires.

Male Animals Are Not Consistently More Aggressive Than Females

The fact that men are not more aggressive than women when individual behavior is carefully analyzed, as cited above, should stimulate a fresh look at the sex differences in animals. Indeed there are indications in the literature that females may be as aggressive as males even in those animal species whose behaviors are usually cited as proving the opposite. For example, a recent paper by two top experimenters in the field (DeBold & Miczek, 1984) begins the discussion as follows:

The present experiments illustrate the complexity of the sexual dimorphism in the aggressive behavior of rats. Females are not, as is commonly stated much less aggressive than males. In fact, they are more aggressive than males toward unfamiliar females. More correctly, male and female rats are sexually dimorphic in terms of the stimuli which elicit aggression and not in terms of males being aggressive and females nonaggressive.

In order to analyze the question in detail, it is necessary to consider the various types of aggressive behavior in animals. Five types will be distinguished here:

- offense against strange conspecifics; - competitive fighting; - maternal aggression; - defense; - predation.

Offense against strange conspecifics and competitive fighting are both under the control of an offense-motivational system, and maternal behavior may well be under its control as well. Defense is controlled by another system, a distinction which is agreed upon by a wide range of investigators (Adams, 1979). Predation is not a social behavior at all, but a behavioral system used to obtain food.

Since we know the brain mechanisms of aggression best from research on the rat, I will begin this discussion with a review of the hormonal factors in the control of rat aggressive behavior (Adams, 1983b).

In the rat there is a special androgen effect which enhances male aggression (offense) against other unfamiliar male rats. I have proposed that the effect is due to a sensory analyzer which is tuned to androgen-dependent pheromones and which facilitates an offense-motivational

3 mechanism. This is responsible for the tendency of certain dominant males to establish and defend territories.

In many other mammals there appears to be a similar brain mechanism that enhances intermale fighting. It may be associated with male territoriality in some species and with intermale displays and fighting in the presence of females during the breeding season in other species. This fighting can be quite spectacular in species with sexual dimorphism in which the males have developed special tusks or antlers which are used in the fighting. It is this phenomenon, well publicized by mass media, which makes many people think that animal aggression is primarily by males.

There are many mammalian species which contradict the popular image because females are as territorial (and in some cases more so) as males against unfamiliar members of their species. I have reviewed this among muroid rodents and found that it is the case in the following genera and species: Rattus rattus; Mesocricetus; Sigmodon; Notomys alexis; Otomys; and Microtus. Also, under wild conditions, laboratory species such as rats and mice are more aggressive in general against unfamiliar intruders, and females in particular are more aggressive than in the laboratory. As a result, laboratory studies systematically underestimate female aggression. I have suggested that the decreased offense of laboratory animals may be due to a tendency for colony odors of laboratory animals to be more homogeneous, thus reducing the activation of the sensory analyzer for unfamiliar pheromones in the laboratory (Adams, 1980).

Pregnant and lactating females are especially aggressive in most mammalian species-a type of aggression which is obviously missing from males. In the laboratory rat, this maternal aggression is apparently due to activation of the offense-motivational system, according to recent data in our laboratory being prepared for publication.

There is no reason to think that the intermale aggression cited above is any more "important" or pervasive in mammals than is maternal aggression. In fact, one of the classic studies of wild rats found the most important determinant of a male's territoriality was the extent to which the male's mother had shown maternal aggression and protected her territory against the intrusion of other rats (Calhoun, 1962). A similar situation seems to hold in primates where the phenomenon has been studied; among Japanese macaques, dominant males are the sons of dominant females (Eaton, 1976).

Competitive fighting, which consists of fighting over food under conditions of starvation, is an important type of aggression which may be more pronounced in females than in males. It is apparently a special case of offense. Although the earliest study we published showed no sex differences, more recent data from our laboratory indicates that females have higher levels of competitive fighting than males in the laboratory rat. Our preliminary data indicate that this is due to a specific effect of estrogen on the offense-motivational mechanism. In any case, there is certainly no reason to say that males are more aggressive than females under these conditions.

As a general rule there is no sex difference in predation in those species in which this non-social form of aggression is found. This is the case not only in carnivores, but in other mammals. There is, for example, no sex difference in the mouse-killing behavior of rats.

Defense, as opposed to offense, is a type of aggression used against predators and other threatening species as well as against threatening animals of the same species. As a rule there is no sex difference in defense among most mammalian species. This is especially true for the biting defensive attack. Some might claim an exception in the greater tendency for male rats to show boxing in response to footshock, but I believe that this reflects the size differential of males

4 and females, and is easily controlled by testing males and females in differing cages of a size proportional to body size.

In sum, we may conclude that female mammals are as aggressive as males, unless one narrows the focus to only one particular type of aggression or only one type of laboratory condition. In the broad view, it turns out that certain types of aggression are more pronounced in males, other types more pronounced or exclusive to females, and other types common to both sexes. In any case there is no support here for the myth that humans have inherited a general mammalian tendency for males to be more aggressive than females.

The Complex Relation of Human Aggression to Animal Aggression

Since the first and third assumptions are contradicted, the second assumption is no longer so critical for our examination of the myth that male monopolization of warfare is biologically determined. That is, since male animals are not generally more aggressive than females, and since human institutional behavior is not necessarily a reflection of individual behavior, it does not seem so important if human individual aggression is homologous to that of other animals. However, the question deserves to be addressed.

One must begin with a careful distinction between institutional behavior and individual behavior. We have already seen that institutional behavior includes male monopolization of war and war-related activities, while individual behavior, outside of an institutional context, does not show such a gender difference. In general we may say that the institutionalized behavior of humans has no homologue in animals. By this I mean not only war, but also the complex hierarchical structures, as well as the informal, largely nonverbal systems of communication which, as mentioned earlier, have been described by Henley and many others.

Individual human behavior, on the other hand, may be compared to that of other animals. To make such comparisons, one may extend the type of analysis that I have done on the homologies between the motivational systems of the laboratory rat and the macaque monkey (Adams, 1981); I found a number of motivational systems appeared to be homologous in the two species. By extension, they may be present in humans as well. Two of them involve what is commonly called aggression: offense and defense. It seems likely that offense may be represented in humans by what is commonly called "anger" and "annoyance," while defense may be represented by fear and fear-driven attack.

Basing the analysis on the data of Averill (1982, 1983), I have suggested that most human anger is the expression of an offense-motivational system homologous to that found in the rat and monkey (Adams, 1986). Although the inner part of the system, the offense-motivational mechanism, has remained similar, the outer parts have been transformed in humans. On the sensory side, the analysis of motivation stimuli is now tuned to the actions of the other person rather than to their attributes. In particular, an analysis is made as to whether these actions are "just" or "fair." This obviates the importance of hormonal effects which are prevalent in other animal species and which affect the analysis of the attributes of the opponent, in particular the attribute of androgen- or estrogen-dependent pheromones. On the motor side, motor patterning mechanisms in humans are dominated by verbal behavior rather than action patterns that include physical assault.

Ironically, the evidence indicates that anger against injustice, which I have suggested is a human homologue of animal offense, is a critical component to the consciousness development of peace

5 activists (Adams, 1986). Since anger against injustice, as shown in the data of Averill (1982, 1983), is as pronounced in women as in men, there is no reason to suggest that it underlies the gender difference in human warfare and its related social institutions.

Conclusion

In conclusion, I think we can categorically reject the myth that gender differences in human warfare reflect a biological basis. Two of the three logical assumptions necessary to support the myth are not supported by the evidence. Male animals are not generally more aggressive than females, and human institutional behavior is not a direct reflection of human individual behavior.

Unfortunately, the myth persists and has political effects. The most systematic study indicates that about half of the college students around the world believe the myth, and our evidence indicates that people who believe the myth are less likely to work for peace (Eckhardt, 1972; Adams & Bosch, 1987).

If the evidence does not support it, what then is the origin of this myth? I submit, as a working hypothesis, that the myth is a projection of our human institutional situation onto our models of animal behavior. To quote a favorite animal behavior study, "Most studies of physiology and behavior, in which the wild Norway rat or its various domesticated breeds have been used as subjects. ..have been based upon hypotheses primarily formulated on the basis of clinical studies on man" (Calhoun, 1962). Perhaps there has been some improvement, but these words seem as valid today as when they were written thirty years ago. Most investigators still establish situations in which males are the subjects and other males are their targets, intruders, or cage-mates. Experiments which use pregnant or lactating females, competitive fighting, or female subjects are becoming more frequent, but are still the exception rather than the rule.

It is my hope that the bias toward use of male subjects is beginning to change. At the 1984 meetings of the International Society for Research on Aggression, hosted by Lagerspetz and her colleagues, almost half of the papers on animal aggression used female subjects. It is important that the textbooks change as well. Finally, we can look forward to the day when the myth that male animals are more aggressive than females can no longer be used by those who would argue that war is product of biology rather than culture.

References

Adams, D. B. (1979). Brain mechanisms for offense, defense, and submission. The Behavioral and Brain Sciences, 2,200-241.

Adams, D. B. (1980). Motivational systems of agonistic behavior in muroid rodents: a comparative review and neural model. Aggressive Behavior, 7, 5-18.

Adams, D. B. (1981). Motivational systems of social behavior in male rats and stumptail macaques: Are they homologous? Aggressive Behavior, 7,5-18.

Adams, D. B. (1983a). Why there are so few women warriors. Behavior Science Research, 18, 196-212.

6 Adams, D. B. (1983b). Hormone-brain interactions and their influence on agonistic behavior. In B. B. Svare (Ed.), Hormones and Aggressive Behavior. New York: Plenum.

Adams, D. B. (1984). There is no instinct for war. Psychological Journal (Moscow), 5, 140-144.

Adams, D. B. (1986). The role of anger in the consciousness development of peace activists: Where physiology and history intersect. International Journal of Psychophysiology, 4, 157-164.

Adams, D. B. (1989). The Seville Statement on Violence: A progress report. Journal of Peace Research, 26, 113-121.

Adams, D. B., & Bosch, S. (1987). The myth that war is intrinsic to human nature discourages action for peace by young people. In J. M. Ramirez, R. Hinde, and J. Groebel, (eds.), Essays in violence. Seville, Spain: University of Seville.

Averill, J. R. (1982). Anger and Aggression: An essay on emotion. New York: Springer-Verlag.

Averill, J. R. (1983). Studies on anger and aggression: Implications for theories of emotion. American Psychologist, 38, 1145-1160.

Calhoun, J. B. (1962). The Ecology and Sociology of the Norway Rat. Public Health Service Publication 1008.

DeBold, J. F., & Miczek, K. A. (1984). Aggression persists after ovariectomy in female rats. Hormones and Behavior, 18, 177-190.

Eaton, G. G. (1976). The social order of Japanese macaques. Scientific American, 235,96-106.

Eckhardt, W. (1972). Crosscultural theories of war and aggression. International Journal of Group Tensions, 2, 36-50.

Groebel, J., & Hinde, R. A. (1989). Aggression and war: Their biological and social bases. Cambridge: Cambridge University Press.

Henley, N. M. (1977). Body politics: Power, sex, and nonverbal communication. Englewood Cliffs, New Jersey: Prentice-Hall.

Lagerspetz, K. (1985). Are wars caused by aggression. In F. L. Denmark (Ed.), Social/Ecological Psychology and the Psychology of Women. Elsevier (North-Holland).

Murdock, G. (1937). Comparative data on the division of labor by sex. Social Forces, 15,551- 553.

Somit, A. (1990). Review essay: Humans, chimps, and Bonobos: The biological bases of aggression, war, and peacemaking. Journal of Conflict Resolution, 34, 553-582.