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time men spend in varies Differences in across cultures, fathers spend less Contribute to Important Differences time interacting with and caring for their children than do mothers in Between Men and Women all cultures that have been studied 1 (see Geary, 1998). David F. Bjorklund and Todd K. Shackelford Yet males spend more Department of Psychology, Florida Atlantic University, Boca Raton, Florida time caring for their offspring than is typical for male mammals. One factor contributing to this unusually cludes evolved psychological Abstract high level of paternal investment is mechanisms that require input Parental investment theory ’ extended childhood. such as social norms and cultural addresses differences that Humans spend more time as juve- beliefs for their operation, and dif- result from the trade-off be- niles than other primates, needing ferent behavioral outcomes will re- tween effort and many years to develop the brain sult from these evolved mecha- effort. For example, and the knowledge necessary to nisms in different environments. In relative to men, women spend navigate the complexities of society. this article, we apply a theory moti- more time caring for offspring, This prolonged immaturity requires vated by such evolutionary psy- are more selective in assenting a supportive environment to which chological logic, parental invest- to sexual intercourse, are more both mothers and fathers ideally ment theory (Trivers, 1972), to upset by a partner’s emotional contribute. Evidence from many interpret some well-documented infidelity than by a partner’s cultures and historical records indi- sex differences. sexual infidelity, and are better cates that the death rate of offspring According to an evolutionary able to inhibit their behaviors increases as a function of father’s psychological perspective (see in certain situations. These and absence, particularly in harsh envi- Buss, 1994), ancestral men and other sex differences are attrib- ronments (see Geary, 1998). Thus, women faced different adaptive utable to evolved mechanisms whereas mothers opt to invest sub- problems that threatened their sur- that work in interaction with stantially in their children’s care vival and reproduction. As a result, the physical and social envi- after birth in order to ensure their they evolved different psychologi- ronments. offsprings’ survival, the case is not cal mechanisms, and evidence of as clear-cut for fathers, particularly this ancient heritage is apparent in Keywords when one considers the number of modern humans (for a review, see parental investment theory; additional offspring men can have Buss, 1994). Parental investment ; sex- by investing more effort in mating. theory accounts for many of these ual strategies Women also may choose to invest differences. According to this theo- less in the care of a child and more ry, there is a conflict for both males in mating, but the caloric costs and Sex differences in behaviors tra- and females in how much time, ef- duration of and nursing ditionally have been attributed to fort, and resources to invest in mat- (in traditional societies today, and “social” factors, because of the pre- ing versus parenting. For many surely in our evolutionary past, sumed flexibility of human behav- species, including humans, males nursing extends to the age of 3 or 4 ior. Proposals that evolved mecha- need to invest substantially less in years) reduce the number of chil- nisms explain why men and parenting than females to achieve dren a woman can expect to have in women behave as they do have successful reproduction. In mam- her lifetime. been regarded warily because of mals, fertilization and gestation There is evidence that paternal the belief that “biological” causa- occur within the female, and, after investment influences socialization tion (including evolutionary caus- birth, mothers provide the primary practices and the amount of es) implies biological determinism. nutritional support for their off- parental investment subsequent Modern evolutionary psychologi- spring until they are weaned. Male generations devote to their off- cal theory, however, makes no such investment in offspring may be as spring (Belsky, Steinberg, & Draper, claims, but argues that contrasting little as the sperm produced during 1991). In environments where fa- “social” with “evolutionary” expla- copulation. In humans, paternal in- thers are absent or where there is nations is a false dichotomy (see vestment is not essential for a marital discord, the resulting stress Tooby & Cosmides, 1992). From man’s offspring to reach adult- produces harsh and inconsistent this perspective, human nature in- hood, and although the amount of child care and insecure attachment.

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Under such situations, children ancestral females who were selec- vestment of the female comes at reach puberty early, form short- tive in mating. Because of the long considerable cost but brings with it term and unstable relationships, period of immaturity in humans, certainty of maternity. In contrast, and invest relatively little in their ancient women’s reproductive in- males, who may invest only sperm own offspring. In stressful and un- terests were often best served by and the energy necessary to copu- certain environments, there is a ten- selecting a mate who not only late, cannot be certain of paternity. dency to invest more in mating (for would provide good genes (e.g., as Furthermore, because women con- both ) than in parenting. The signaled by facial symmetry; ceal and are potentially pattern is reversed for children Shackelford & Larsen, 1997), but sexually receptive throughout their growing up in harmonious homes who also would invest in her and , it is difficult for a and homes where the father is pres- her offspring. Over evolutionary man to know when copulation is ent; such children mature later, time, it was also in men’s reproduc- likely to result in pregnancy. As a postpone sexual activity, and dis- tive interests to see to it that their result, being the unwitting social greater investment in the fewer offspring received the support nec- father to another man’s genetic off- children they produce. In sum, the essary to survive to reproductive spring is a possibility for men. This availability of resources, which is age. But the amount and duration in fact occurs in between 2% and related to paternal investment and of investment necessary to ensure 30% of all births; the rate is similar spousal harmony, leads to different the survival of offspring was less in traditional societies, and there is patterns of socialization, resulting for men than for women. Thus, al- no reason to believe that it differed in differential parental investment though both men and women substantially for our ancestors (see in the next generation. shared a common reproductive Baker & Bellis, 1995). Women, of The differential investment of goal (getting their offspring to course, cannot so easily be fooled males and females in their off- adulthood), the optimal level of in- into rearing another woman’s child spring has resulted in the evolution vestment to achieve this goal was who they believe is their own, al- of different ways of behaving and unequal for the sexes, placing though they do risk losing a mate’s thinking in men and women. males’ and females’ reproductive investment to another woman. Although these differences are gen- interests in conflict. One consequence of this sex dif- erated by evolved psychological Men are not indiscriminate ference in the certainty of genetic mechanisms, they are more vari- when it comes to selecting a mate, parenthood can be seen in men’s able than is typical in mammals. especially when selecting a long- and women’s reactions to a long- Here, we discuss two areas in term partner. Men around the term partner’s infidelity. When which men and women behave and world want long-term partners asked to imagine that their long- think differently, as predicted by who are attractive, intelligent, and term partner is either (a) having ca- parental investment theory: sexual kind. Women also desire attractive, sual sex with another person or (b) strategies and inhibitory abilities. intelligent, and kind men as hus- developing a close emotional rela- bands, but, as predicted by tionship with another person, men parental investment theory, they and women respond differently. SEXUAL STRATEGIES rate financial resources as more im- Verbal reports and measures of portant in a mate than do men physiological arousal indicate that (Buss, 1989). Despite the selectivity women are more upset by a part- One class of sex differences that that men and women universally ner’s emotional infidelity, which can be understood in terms of display in choosing a long-term could signal a loss of resources, parental investment theory is sexu- partner, and consistent with whereas men are more upset by a al strategies (Buss, 1994). Males in parental investment theory, women partner’s sexual infidelity (Buss, most mammals can achieve are more selective in granting sex, Larsen, Westen, & Semmelroth, tremendous and men are more eager to have ca- 1992). by inseminating many females, sual sex (see Buss, 1994). In conclusion, human sex differ- making males relatively indiscrim- Men and women have evolved ences in parental investment predict inate when it comes to choosing a different psychological mecha- sex differences in sexual strategies. sex partner. Females, in contrast, nisms as solutions to the adaptive These sex differences include the have much more invested, at least problems unique to their sex. For greater inclination of men to pursue potentially, in a single copulation. example, fertilization occurs within short-term casual sex; the greater The possibility of pregnancy, and the female, and it is the female who selectivity of women in choosing a the time and energy spent caring gestates and gives birth to the off- mate, especially in the context of for the resulting offspring, favored spring. This greater prenatal in- short-term mating; and the greater

Copyright © 1999 American Psychological Society 88 VOLUME 8, NUMBER 3, JUNE 1999 distress of men in response to a desires and resisting distractions tionary history, provide the skeletal long-term partner’s sexual infideli- that would take them away from features for adapted behaviors. ty and of women in response to a their infants. They also must inhib- They represent biases that, in the partner’s emotional infidelity. it toward infants or distant past, served men’s and young children who may cry con- women’s reproductive fitness well. tinuously, disobey, and damage However, humans exert greater in- INHIBITORY ABILITIES personal property. tentional control over sexual be- In support of these hypotheses, havior than any other animal, and research has shown that women the evolved sexual and child-care Inhibition refers to the withhold- are better able to control the ex- strategies of men and women are ing of a response in situations in pression of their emotions than are not invariantly manifested, but in- which that response otherwise men, despite the fact that women stead are responsive to physical would be made. The ability to in- are more emotionally expressive and social environments over the hibit inappropriate sexual and ag- than men. In studies in which peo- course of development. From this gressive responses is important for ple are asked to display a positive perspective, nature and nurture are the success of both men and women emotion after a negative experience not alternative explanations, but in modern (and presumably ances- (e.g., pretending that a foul-tasting instead are two sides of the same tral) society and may have played a drink tastes good) or vice versa, fe- explanatory coin. role in the evolution of human intel- males (from the age of 4 years and ligence, particularly social intelli- up) are better able to control their Recommended Reading gence (Bjorklund & Harnishfeger, emotional expressions (i.e., fool a 1995). However, ancestral women judge watching their reactions) Bjorklund, D.F., & Kipp, K. (1996). may have needed greater inhibitory than are males (e.g., Cole, 1986). In (See References) abilities than ancestral men in other research, there is evidence Buss, D.M. (1994). (See References) certain contexts, because of their Buss, D.M. (1999). Evolutionary psy- that females are better than males chology: The new science of the different reproductive strategies on tasks that involve resisting mind. Needham Heights, MA: (Bjorklund & Kipp, 1996). For exam- temptation and delaying gratifica- Allyn & Bacon. ple, because of ancestral women’s tion (e.g., Kochanska, Murray, Geary, D.C. (1998). (See References) greater investment in the potential Jacques, Koenig, & Vandegeest, Trivers, R. (1972). (See References) consequences of an act of copula- 1996), precisely the pattern one tion, it might have been in their re- would predict if selection pressures Acknowledgments—We would like to productive interests to have greater associated with child care were thank , David Geary, Erika control of their sexual arousal and greater on ancestral females than Hoff-Ginsberg, Martha Hubertz, Gregg related behaviors in order to more on ancestral males. And there is LeBlanc, Santo Tarantino, Robin Vallacher, and Viviana Weekes, who pro- closely evaluate the value of a man limited evidence that women are vided helpful comments and sugges- before assenting to sex. Ancestral better able to inhibit sexual arousal tions that improved this article. women also may have needed sub- than are men (Cerny, 1978; Rosen, stantial political skill in order to 1973). In contrast, there is no fe- keep sexual interests in other men male advantage in inhibitory abili- Note hidden from a mate. Male response ties for cognitive tasks such as se- to suspected female infidelity can lective attention, suggesting that 1. Address correspondence to either be violent, and even when adultery the sex differences are relatively David F. Bjorklund, Department of does not lead to aggression, it often domain-specific, restricted to abili- Psychology, Florida Atlantic Uni- leads to divorce, which both histor- ties related to sexual and parenting versity, Boca Raton, FL 33431, e-mail: ically and in contemporary societies contexts, as predicted by parental [email protected], or Todd K. is more detrimental to a woman and Shackelford, Division of Science— investment theory. Psychology, Florida Atlantic Uni- her offspring than to a man (see versity, 2912 College Ave., Davie, FL Buss, 1994). 33314, e-mail: [email protected]. Similarly, the bulk of child-care CONCLUSIONS responsibilities falls to women, and References these also may require enhanced inhibitory abilities. For example, Different psychological mecha- Baker, R.R., & Bellis, M.A. (1995). Human sperm often must put the needs of nisms in men and women, attribut- . London: Chapman & Hall. Belsky, J., Steinberg, L., & Draper, P. (1991). their infants ahead of their own, able to sex differences in minimum Childhood experience, interpersonal develop- delaying gratification of their own parental investment over evolu- ment, and reproductive strategy: An evolu-

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tionary theory of socialization. Child Buss, D.M., Larsen, R.J., Westen, D., & Rosen, R.C. (1973). Suppression of penile tumes- Development, 62, 647–670. Semmelroth, J. (1992). Sex differences in jeal- cence by instrumental conditioning. Bjorklund, D.F., & Harnishfeger, K.K. (1995). The ousy: Evolution, physiology, and psychology. Psychometric Medicine, 35, 509–514. role of inhibition mechanisms in the evolution Psychological Science, 3, 251–255. Shackelford, T.K., & Larsen, R.J. (1997). Facial of human cognition. In F.N. Dempster & C.J. Cerny, J.A. (1978). Biofeedback and the voluntary asymmetry as an indicator of psychological, Brainerd (Eds.), New perspectives on interference control of sexual arousal in women. Behavior emotional, and physiological distress. Journal and inhibition in cognition (pp. 141–173). New Therapy, 9, 847–855. of Personality and , 72, York: Academic Press. Cole, P.M. (1986). Children’s spontaneous control 456–466. Bjorklund, D.F., & Kipp, K. (1996). Parental invest- of facial expression. , 57, Tooby, J., & Cosmides, L. (1992). The psychological ment theory and gender differences in the evo- 1309–1321. lution of inhibition mechanisms. Psychological Geary, D.C. (1998). Male, female: The evolution of foundations of culture. In J. Barkow, L. Bulletin, 120, 163–188. human sex differences. Washington, DC: Cosmides, & J. Tooby (Eds.), Buss, D.M. (1989). Sex differences in human mate American Psychological Association. (pp. 19–136). New York: Oxford University preferences: Evolutionary hypotheses tested in Kochanska, G., Murray, K., Jacques, J.Y., Koenig, Press. 37 cultures. Behavioral and Brain Sciences, 12, A.L., & Vandegeest, K.A. (1996). Inhibitory Trivers, R. (1972). Parental investment and sexual 1–49. control in young children and its role in selection. In B. Campbell (Ed.), Buss, D.M. (1994). . New York: emerging internalization. Child Development, and the descent of man (pp. 136–179). New York: Basic Books. 67, 490–507. Aldine de Gruyter.

came to be, only that it came to be. The Clustering and Contagion By contrast, contagion refers to a of Suicide possible explanation (as I argue later, a fairly vague explanation) of Thomas E. Joiner, Jr.1 why a cluster developed. Clusters Department of Psychology, Florida State University, Tallahassee, Florida (of a sort) appear to occur, but the status of contagion as the reason for such occurrences is more equivocal. Abstract (a risk that may be offset by Two general types of sui- good social support). cide cluster have been dis- CLUSTERS—OF A SORT— cussed in the literature; Keywords APPEAR TO OCCUR roughly, these can be classi- suicide clusters; suicide con- fied as mass clusters and tagion point clusters. Mass clusters Given that attempted and com- are media related, and the ev- pleted suicides are relatively rare, idence for them is equivocal; The phenomena of attempted and given that they tend to be point clusters are local phe- and completed suicide are trou- more or less evenly distributed in nomena, and these do appear bling and mysterious enough in space and time (e.g., suicides occur to occur. Contagion has not themselves; the possibility that sui- at roughly the same rate in various been conceptually well devel- cide is socially contagious, even regions of the United States and oped nor empirically well more so. This article considers occur at roughly the same rate re- supported as an explanation whether suicide clusters exist, and gardless of the day of the week or for suicide clusters. An alter- if so, whether “contagion” process- the month), it is statistically un- native explanation for why es can account for them. likely that suicides would cluster suicides sometimes cluster is There is a potentially important by chance alone. Yet cluster they articulated: People who are distinction between the terms sui- do, at least under some circum- vulnerable to suicide may cide cluster and suicide contagion. stances. (Such clustering is often cluster well before the occur- A cluster refers to the factual oc- termed the “Werther effect,” after rence of any overt suicidal currence of two or more complet- a fictional character of Goethe’s stimulus, and when they ex- ed or attempted suicides that are whose suicide purportedly in- perience severe negative nonrandomly “bunched” in space spired actual suicides in 18th-cen- events, including but not lim- or time (e.g., a series of suicide at- tury Europe.) Two general types of ited to the suicidal behavior of tempts in the same high school or suicide cluster have been dis- one member of the cluster, all a series of completed suicides in cussed in the literature: mass clus- members of the cluster are at response to the suicide of a ters and point clusters. Mass clus- increased risk for suicidality celebrity). The term cluster implies ters are media related; point nothing about why the cluster clusters, local.

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