BEHAVIORAL AND BRAIN SCIENCES (1999) 22, 203–252 Printed in the United States of America Staying alive: Evolution, culture, and women’s intrasexual aggression Anne Campbell Psychology Department, Durham University, Durham DH1 3LE, England [email protected] Abstract: Females’ tendency to place a high value on protecting their own lives enhanced their reproductive success in the environment of evolutionary adaptation because infant survival depended more upon maternal than on paternal care and defence. The evolved mech- anism by which the costs of aggression (and other forms of risk taking) are weighted more heavily for females may be a lower threshold for fear in situations which pose a direct threat of bodily injury. Females’ concern with personal survival also has implications for sex dif- ferences in dominance hierarchies because the risks associated with hierarchy formation in nonbonded exogamous females are not off- set by increased reproductive success. Hence among females, disputes do not carry implications for status with them as they do among males, but are chiefly connected with the acquisition and defence of scarce resources. Consequently, female competition is more likely to take the form of indirect aggression or low-level direct combat than among males. Under patriarchy, men have held the power to prop- agate images and attributions which are favourable to the continuance of their control. Women’s aggression has been viewed as a gen- der-incongruent aberration or dismissed as evidence of irrationality. These cultural interpretations have “enhanced” evolutionarily based sex differences by a process of imposition which stigmatises the expression of aggression by females and causes women to offer excul- patory (rather than justificatory) accounts of their own aggression. Keywords: aggression; competition; evolutionary psychology; female; sex differences; sociobiology; violence Introduction is on measures of indirect aggression (gossiping and os- Analyses of male and female patterns of involvement in ag- tracising) – I will return to this fact below. gression suggest four important facts that any adequate the- 3. There is a high correlation between rates of male and ory must explain. female aggression across geographical areas. Rohner (1976) reported a correlation between male and female rates of ag- 1. Human males engage in aggression more frequently ϭ than females from about the age of two onward. Childhood gression of r .88 for both children and adults across a sex differences in aggression are universal (Rohner 1976; world sample of 101 societies. The correlation over 66 na- Whiting & Edwards 1973). Adult differences measured by tions reporting criminal assault data to Interpol is .99. In England and Wales, rates of male and female violent crime anthropological report (Brown 1991; Ember 1981) and by ϭ criminal statistics likewise appear to be universal. Simon and correlate r .98 over 43 police jurisdictions. In a study of Baxter (1989) obtained homicide data from 31 countries for 34 police reporting districts in Massachusetts, the correla- three time periods spanning 1962 to 1980. They calculated tion over region for male and female aggravated and simple the percentage of female arrests and found no time or coun- assault was .90 (Campbell et al., submitted). try in which female rates exceeded that of males. The mean 4. There is a high correlation between rates of male and percentage of female arrests was 10.56% (s.d. ϭ 5.55). female aggression over age. In both sexes criminal violence 2. The sex differential increases with increasing serious- ness of the measure of aggression. Men in the United States commit 85.53% of simple assaults, 87.31% of aggravated as- Anne Campbell is Reader in Psy- saults, and 88.5% of murders (Kruttschnitt 1994). Women’s chology at Durham University, Eng- proportionate involvement in violent crime has remained land. She gained her doctorate in ex- stable over the last 30 years (Kruttschnitt 1993). At sub- perimental psychology from Oxford criminal levels, recent meta-analyses have indicated that University in 1977. Since then she has the sex difference is greater for physical aggression than for worked in Britain and the United verbal or psychological aggression (Bettencourt & Miller States on female adolescent aggres- sion, girls’ involvement in street 1996; Eagly & Steffen 1986; Hyde 1986; Knight et al. 1996) gangs, men and women’s social representations of ag- and this is in agreement with prior narrative reviews of the gression, the developmental trajectory of sex-typed be- literature (Frodi et al. 1977). The magnitude of these sex haviour and, most recently, applying evolutionary psy- differences in psychological research has remained stable chology to the analysis of sex differences in aggression from the mid-1960s (Knight et al. 1996). The only form of and violence. aggression in which girls and women exceed boys and men © 1999 Cambridge University Press 0140-525X/XX $12.50 203 Campbell: Staying alive is most likely between the ages of 14 and 24 (Campbell critical importance of the mother’s survival for her own re- 1995a) with the female peak occurring approximately two productive success. In addition, using a co-evolutionary years earlier than that of males, in line with females’ earlier perspective, I will consider how patriarchal culture has dis- attainment of puberty. The correlation between the sexes torted our understanding of women’s aggression. over age is .89 for assault, and .99 for aggravated assault I will begin by describing the greater importance of per- based on U.S. data and .98 for U.K. crime statistics. Stud- sonal survival for female inclusive fitness, which renders the ies of aggression in children have also noted the remarkable costs of direct aggression greater for females than for males. similarity of the age curves (Bjorkqvist et al. 1992; Eron et I will argue that these differential cost-benefit outcomes al. 1983). were and are mediated by differences in fear of physical Men’s violence has already received considerable scru- harm in men and women. The greater need for women to tiny by evolutionary psychologists (Daly & Wilson 1988a). avoid serious physical injury has implications for the for- In species where one sex makes a higher parental invest- mation of dominance hierarchies. Though achievement of ment than the other, the high investing sex is a resource for high rank may confer advantages in terms of resource ac- which the opposite sex competes. In humans as in many cess, the establishment of hierarchies and the pursuit of other species, females make a higher parental investment dominance within them is more costly for females than for than do males. The reproductive strategies of women com- males. Primate and human research bearing on sex differ- pared to men can be seen as reflecting concern with “qual- ences in dominance hierarchies and status seeking will be ity versus quantity.” Females’ reproductive success is con- reviewed. Although females show less concern with status strained by the long period of gestation and lactation (and than do males, they must be concerned with securing re- resources necessary to sustain these) required for each off- sources. Such disputes, however, are likely to be low risk or spring, while males’ success is constrained by the number indirect in form. Psychological and criminological studies of partners they can inseminate. In line with this, evidence pertinent to this argument will be reviewed. I will then con- suggests that humans have a prehistory of mild polygyny sider how patriarchy awarded men the power to create and (i.e., men tended to seek mating opportunities with multi- disseminate cultural images which enhanced the male mo- ple females). This is apparent in our universal sexual di- nopoly on aggression by characterising female aggression as morphism, earlier male senescence and death, earlier fe- either an abnormal attempt to mimic male aggression or as male sexual maturity, longer male reproductive career, evidence of psychopathology. relatively large male sexual organs, and a higher preferred rate of copulation by men (Daly & Wilson 1988a; Mitani et al. 1996; Oliver & Hyde 1993; Symons 1979). The fact that 1. Evolutionary factors affecting form some dominant males will monopolise more than their fair of female aggression share of females means that other males will face “repro- ductive death.” Thus competition among males is high be- 1.1. Maternal investment and the need cause the associated payoffs in terms of reproductive suc- for personal survival cess are high also. Dominance and resource holding are In this section I will argue that the mother’s presence is linked among males. Both are part of the same evolved sys- more critical to her offspring’s survival and hence to her re- tem used by males to attract females. As Wilson and Daly productive success than is the father’s. This point is impor- (1985, p. 60) note, “males are in competition for those re- tant because it forms the basis for the argument that fe- sources, including feeding territories, nest sites and more males should be more concerned with staying alive than are intangible ‘resources’ like political influence and social sta- men and this in turn accounts for their low-risk and indirect tus that can be converted into reproductive opportunity, strategies of dispute resolution. whether because they are directly attractive to females or Lower fitness variance among females means that more because they help quell rival males.” Daly and Wilson females than males can expect to produce at least one child (1994) in a series of studies have argued that the higher rate in their lifetimes. Though a successful male can always out- of aggression in men is indicative of the crucial importance reproduce a successful female, the principal difference be- of status competition to male reproductive success. Males tween the sexes is the relative certainty of at least minimal engage in dangerous confrontations and other forms of lifetime reproduction.