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8 Human Bulletin, 26(2), 2011

environment, echoing the Marxian dictum ʺDas Sein bestimmt das Bewußtseinʺ. To be convinced that an important part of our history is Theoretical phylogeny and that our ancestors have been shaped by mutations and the forces of selection and to defend that position demands a strong Articles person. In two books, Hiram Caton criticized radical feminism and other political movements Understanding Sex for trying to undermine the family as the basic unit of society and its crucial role for successful Differences in Human early . Mortality Rates through Hiram was courageous in the choice of his Tinbergenʹs Four Questions research topics and in making his findings public. In contrast to many members of the By Daniel J. Kruger older (my) generation, he really came to grips School of Public Health, University of Michigan, with computer technology and all the new Ann Arbor, MI 48109 options it facilitates. Hiram served as ISHE Information Officer from 2005 to 2008, and we And Carey J. Fitzgerald on the board of ISHE benefitted from his drive Department of , Central Michigan University, Mount Pleasant, MI 48859 and knowledge. He urged us to have a better relationship with the scientific press and the Abstract academic world. Yet, we still donʹt have a Sex differences in human mortality rates ʺpress roomʺ where new findings from ISHE emerge from a complex interaction of genetic colleagues would be presented, in a heritage and developmental environment. professional way, to those who mediate them to Although mortality is not in itself a behavior, it the interested public. Other scientific societies is an indirect product of behavior and and especially big scientific institutions (e.g. the physiology and thus responsive to life history Senckenberg Gesellschaft für Naturforschung in variation in resource allocation, behavioral Germany) have gone this way by now. We in tendencies, and relevant environmental the board of ISHE will have to see how we will conditions. The explanatory framework of position ourselves, a relatively small Tinbergenʹs Four Questions is sufficiently international society, in the shark tank out powerful in generalization to promote there. understanding of this phenomenon. Excess I thank Hiram for his role in a crucial time of male mortality is a result of a trade‐off between ISHE and we will miss his company, his competitiveness and longevity. Male life history Australian humor, his provocative ideas, and gives greater emphasis to reproductive effort at the talks around a fireplace. the expense of somatic effort, and mating effort at the expense of longevity compared to female Wulf Schiefenhövel, Ph.D., co-founded life history. Men exhibit riskier behavioral ethnomedicine in Germany, performing field studies in New Guinea on traditional medical patterns and greater physiological beliefs and practices. Since then, he has done susceptibility, dying at higher rates from continuous fieldwork in ethnomedicine, behavioral and most non‐behavioral causes , and human ethology, mainly in across the lifespan. The magnitude of the sex Melanesia and Indonesia, authoring 300 papers, either authoring, coauthoring, or coediting 24 difference in mortality in developed nations books, and publishing scientific films. peaks when males sexually mature and enter

Human Ethology Bulletin, 26(2), 2011 9

into mating competition. Social and reductionism necessary to isolate independent environmental conditions intensifying male mechanisms and the holistic understanding of competition for resources, status, and mates the interrelationships among causes and lead to increased male mortality. mechanisms. Tinbergen includes the evolutionary (ultimate and integrative) causal Keywords: Tinbergen, Four Questions, Sex explanations of adaptation (function) and Differences, Sexual Selection, Mortality phylogeny (evolutionary history), as well as the Introduction necessarily mechanistic explanations of more immediate (proximate) causal mechanisms and Being male is now the single most prominent their ontogeny (developmental processes) demographic risk factor for early mortality in during the lifespan of the individual. highly developed societies (Kruger & Nesse, 2006). Numerous studies document sex Before discussing sex differences in mortality differences in longevity and mortality rates, yet rates, it may be informative to outline those researchers lacking an evolutionary evolutionary theory regarding mortality in framework are still grasping for a full general. One may initially wonder why understanding despite statistically powerful evolutionary processes occurring over billions data driven models (e.g., Rogers, Hummer, & of years and millions of generations have not Nam 2000). Darwin (1871) considered male led to perfected complex organisms that can intrasexual competition the best explanation for live indefinitely. However, the processes of why mammalian males are significantly more natural and sexual selection maximize the physically aggressive than females. Long after survival of genes rather than the survival of Darwin’s insights, most explanations of sex individuals or species (Williams, 1957; differences in human aggression, violence, and Dawkins, 1976). Building and maintaining a mortality are still based only on proximate body is in the service of reproduction: our factors. In the past few decades there has a been bodies are essentially vehicles for the a revival of the recognition that such sex propagation of genetic information. The effort differentials emerge from an interaction of an individual expends on building and characteristics shaped by sexual selection and maintaining a body is ultimately for the environmental conditions of development (e.g., purpose of reproduction. Daly & Wilson 1978). Many genes have multiple effects (this is Although mortality is not in itself a behavior, it referred to as pleiotropy), which can be both is an indirect product of behavior and beneficial and hazardous based on the physiology and thus responsive to life history developmental and environmental context. variation in resource allocation, behavioral Genes with early benefits but later costs will be tendencies, and relevant environmental selected for because younger individuals have a conditions. Tinbergenʹs (1963) Four Questions higher reproductive value (Medawar, 1952). framework is sufficiently powerful in Selection pressure was greater at younger ages generalization to promote an integrated because few people survived to old age in understanding of this phenomenon. Each of the ancestral environments, thus early acting Four Questions represents a unique and beneficial genes spread faster than late acting necessary aspect for a comprehensive beneficial genes. The cumulative result of these explanation. Such a framework helps illustrate factors is senescence, a decline of physiological the complex network of relationships between function over time (Williams, 1957). The causes emerging at different levels, maintaining relatively higher importance of reproduction at an appropriate balance between the the expense of survival for the sake of longevity 10 Human Ethology Bulletin, 26(2), 2011

also forms the basis for sex differences in The vast majority of complex animal life mortality rates ultimately created by the reproduces sexually across generations. Genetic processes of sexual selection. recombination helps purge harmful mutations, and genotypic variability facilitates adaptation Evolutionary Adaptation to changing environmental conditions Each of Tinbergen’s Four Questions represents (Williams, 1975); competition from other a different, independent but interconnected species (Bell, 1982); predators and parasites aspect of a more comprehensive explanation. In (Williams, 1975); countering the adaptations of this case, it may be most useful to begin the prey to predation; and starvation (Bell, 1982). discussion with the evolutionary history Sexual reproduction entails the combination of underlying sex differences in mortality. The gametes from a pair of parents. Larger gametes ultimate functional framework provides a deep give zygotes greater viability; production of understanding of the systematic origins of smaller gametes gives quantitative advantage excess male mortality, of course not considering and smaller gametes will be relatively more mortality as an adaptation per se. Stable successful than intermediate sized gametes aggregate sex differences result from sexual when large partner gametes are present. Thus, selection, the processes of intra‐sexual there is disruptive selection for gamete size competition and inter‐sexual selection, as well (Bulmer & Parker, 2002). The definition of sex as selective pressures related to sex specific follows from this divergence in gamete size; roles such as gestation. The basic properties of females contribute larger gametes than males sexual reproduction define the male and female (See Figure 1). The cascade of effects sexes, and explain why they differ from each responsible for aggregate differences between other. females and males originates from this sex difference in investment.

Figure 1. Divergent Selection Pressure Leads To the Fundamental Sex Difference in Parental Investment.

Because females usually invest considerably 1972). Male reproductive success is largely more than males in offspring, and are more dependent on securing mating opportunities, limited in the quantity of offspring they can through both intrasexual competition with produce, they are selected to be choosier in other males and by being chosen by females in considering partners (Bateman, 1948; Trivers, intersexual selection because of the

Human Ethology Bulletin, 26(2), 2011 11

attractiveness of their traits and displays competition for reproductive access to females (Darwin, 1871). Male reproductive success is (Bateman, 1948; Trivers, 1972). This selected for driven by sexual access to fecund females and relatively higher male investment in genes enhancing sexual access and offspring reproductive effort at the expense of somatic production will be selected for even if they also maintenance and relatively higher investment increase risk of injury, sickness, and early death in mating effort at the expense of parental effort (Daly & Wilson 1978; Möller, Christe, & Lux (See Figure 2, males allocate more effort to 1999). For example, male guppies devote less aspects highlighted in gold, at the expense of time to foraging when novel females are effort for alternative aspects within sets). present and those able to mate with a series of Compared to women, men on average have unfamiliar females will exhibit lower lifetime greater height and weight, more upper‐body growth, demonstrating the trade‐off between strength, higher metabolic rates, and later somatic and reproductive effort (Jordan & sexual maturity (for a review, see Miller, 1998). Brooks, 2010). These attributes facilitate direct male competition for mates, as well as competition Mammalian male reproductive success usually for the resources and social status that make benefits more than female reproductive success men attractive to prospective partners (Wilson from a greater number of sexual partners and & Daly, 1985). the greater variation in male reproductive success compared to females heightens male

Figure 2. Male Investment Bias in Life History Strategy.

Male tendencies for risky behavior were Male competition can be hazardous, violent, selected for because they ultimately enhanced and sometimes fatal (Betzig, 1986; Kaplan & reproductive success, through the promotion of Hill, 1985). Because sex differences in parental social status, resource control, and success in investment and mating competition are mating competition (Wilson & Daly 1992). ultimately responsible for sex differences in Historically, men who controlled more mortality rates, we predict that the intensity of resources married younger women, married male mating competition (in interactions both more women, and produced offspring earlier within and between groups) will be (Low, 1998). Women across cultures value male proportional to the degree of excess male social status and economic power (Buss, 1989) mortality. and these predict male reproductive success Campbell (1999) concurs that aggression and across a wide variety of societies (see Hopcroft, violence have a much greater role in 2006). There is some differentiation of status reproductive strategies for men than for women even in relatively egalitarian foraging societies, and agrees that sex differences in parental and higher status men have better mating investment are the ultimate explanation. success (Chagnon 1992; Hill & Hurtado 1996). However, she emphasizes the greater potential 12 Human Ethology Bulletin, 26(2), 2011

harm for women’s reproductive success as the 1997; Plavcan, van Schaik, & Kappeler 1995), primary factor, as child survival is threatened larger size and armor of males, and higher male more by maternal than paternal death. Taylor, mortality rates as compared to females Klein, Lewis, Gruenewald, Gurung, and (Leuttenegger & Kelley 1977). After controlling Updegraff (2000) also build on sex differences for the effects of phylogeny, there is a strong in parental investment to argue that in contrast association between sexual size dimorphism to the male biased fight or flight response, and sex differences in mortality across women respond to threats by tending and mammalian taxa, demonstrating the role of the befriending in order to cultivate strong social intensity of sexual selection (Promislow, 1992). bonds and protect the vulnerable. Across vertebrate species, the longevity gap Phylogeny between males and females is predominantly for polygynous species (Clutton‐Brock & Cross‐species comparisons provide valuable Isvaran, 2007). Elephant seals often illustrate insights on the relationship between the properties of polygyny in educational texts reproductive strategies and the relative sex and presentations. Male elephant seals compete difference in mortality rates. Tracing for control of harems of about 30 females and phylogenetic patterns helps reconstruct the male reproductive success is highly skewed. evolutionary origins and history of attributes Males who control harems obtain the vast and behaviors, identifying both promoting and majority of matings and 80% of males die constraining influences on excess male before reproducing. Male development takes mortality. Females typically outlive males twice as long and adult males are three to four across most animal species (Hazzard, 1990), times the size of females (Harvey & Clutton‐ reflecting trade‐offs that increase male Brock, 1985). Similar patterns occur in other reproductive success even at the expense of highly polygynous species such as peacocks longevity (Møller, Christe, & Lux 1999). and peahens. Reproductive patterns influence the intensity of Male compete to gain access to sexual selection for each sex. Sex differences in desirable mates, making displays of status, physiology and behavior follow from the warding off potential competitors with loud degree of polygyny, which could be thought of warning calls, demonstrating strength, fighting as the extent of male reproductive inequality. with other males, and in some species (humans Polygyny is common amongst mammalian and callitrichids) provisioning resources (Buss, species, likely due to the relative male 2005). Male langur monkeys engage in vicious specialization in mating effort and female competitions for control of harems, leading to specialization in infant care and nutritional high levels of male mortality (Hrdy, 1977). provisioning (Low, 2003, 2007; Reichard & When two or more Barbary macaque males are Boesch, 2003). In highly polygynous species, a near an estrous female, they engage in scream few males virtually monopolize reproductive fights and true fights (Kuester & Paul, 1992). In success, creating powerful selection for traits scream fights, males approach each other that lead to success in mating competition, even within 10 meters and begin screaming at each if these traits are also detrimental to the health other. These scream fights may escalate into and longevity of high proportions of true fights, including hitting, thrashing, and individuals (Williams, 1957; Kirkwood & Rose, biting (Kuester & Paul, 1992). The rate of male 1991; Stearns, 1992). Species with higher physical injuries caused by other males degrees of polygyny have greater male increases sharply during mating season, competition and relatively more risky male behavior (Plavcan, 2000; Plavcan & van Schaik

Human Ethology Bulletin, 26(2), 2011 13

demonstrating the association with maximizing the numerical advantage in forming coalitions mating opportunities (Kuester & Paul, 1992). against out‐group males and lower rates of caused by other adult males Male Japanese macaques establish a social (Robbins, 1995). In two multi‐male groups, a dominance ranking system based on physical social dominance hierarchy formed and aggression. Dominant males are more likely to dominant males accounted for 83% of the mate with females during their fertile periods, observed matings (Robbins, 1999). Aggressive though males favored in female mate choice behaviors between male mountain gorillas sired more offspring regardless of their social include grunting, screaming, chest beating, hits, dominance (Soltis et al., 1997). kicks, and bites (Harcourt et al., 1993; Robbins, Mitsunaga, Shimizu, Nozaki, Yanagihara, 1999). Domingo‐Roura, & Takenaka, 1997). In Among bonobos and (common) chimpanzees, savannah baboons, there is a very large positive our closest living relatives, we see correlation between male dominance rank many parallels to human social behavior achieved through successful fights with rival related to male competition. In chimpanzees males and mating success (Alberts, Watts, & there are cases of both inter‐group and intra‐ Altmann, 2003). Male yellow and anubis group male aggression and killings (Boesch, baboons form coalitions to fight a common Head, Tagg, Arandjelovic, Vigilant, & Robbins, male threat; male mating opportunities do not 2007; Fawcett & Muhumuza, 2000). Male chimp strictly follow to their rank in the dominance coalitions systematically raid neighboring hierarchy (Bulger, 1993). Chacma baboons do territories, killing the resident males and not form coalitions, and male mating expanding into their territories (Mitani, Watts, opportunities follow directly from social rank & Amsler, 2010). Larger male bands control (Bulger, 1993). more female territories. As chimpanzees form Male orangutans lead a largely solitary lifestyle, social groups to protect themselves from out‐ using loud “long calls” to keep lower‐ranking group members, intra‐group killings are males out of their vicinity (Galdikas, 1979). extremely rare and may be a result of extreme These calls are effective at signaling the intrasexual competition among males (Wilson dominant males’ location to females and & Wrangham, 2003). For example, Fawcett and keeping lower‐ranking males at bay; however Muhumuza (2000) documented intra‐group they will actually attract fellow dominant male members killing another male in their males, who presumably arrive to displace the cohort when the number of cycling females was calling male. The rare male orangutan extremely low. Both wild (Hill, Boesch, interaction consists of intense physical Goodall, Pusey, Williams, & Wrangham, 2001; aggression over social ranking and/or a desired Goodall, 1986; Nishida, 1990) and captive mate (Mitani, 1990). Like male orangutans, chimpanzee populations (Dyke, Gage, Alford, mountain gorillas are considered to have a one‐ Swenson, & Williams‐Blangero, 1995) have male mating system (Harcourt, 1981). Most higher male than female mortality rates. males do not have to engage in male Bonobos are notable for being a peaceful competition with other resident males for species with very little violence or overt fecund females; physical aggression occurs in intrasexual competition (de Waal & Lantig, encounters with out‐group males and to 1988). Bonobos form matrilineal groups with prevent local females from joining a different strong female alliances that may have led to group (Sicotte, 1993). Still, around 40% of low levels of aggression and sexual coercion mountain gorilla groups are multi‐male (Weber (Wrangham, 1993). Yet male‐male aggression & Vedder, 1983). These males may benefit from 14 Human Ethology Bulletin, 26(2), 2011

increases in frequency and intensity on mating previous killings, acquire resources, elevate days and corresponds to the number of estrous personal prestige, and acquire women. females, and the aggressors mated more often Yanomamo men who have killed have higher than their targets (Hohmann & Fruth, 2003). social status and more wives than those who have not, thus about 40% have killed other men Humans are much less polygynous in (Chagnon, 1988). Violent inter‐tribal conflict comparison to most other primates, but the vast long preceded the arrival of Europeans in the majority of cultures (84% of those documented Americas. Around 1325 CE, half a thousand by anthropologists) allow for polygynyous individuals died violently in a single incident in relationships (Ember, Ember, & Low, 2007) and the Dakotas and none of the remains found the variation in male reproductive success is were of young women (Keeley, 1996). In substantially higher than in female contrast to contemporary fictive depictions, reproductive success. Women favor men with warfare is typically less frequent in tribal abundant access to resources and phenotypic groups after contact with modern societies cues of gene quality (Gangestad & Thornhill, (Keeley, 1996). 1997; Lancaster, 1989; Buss & Schmitt; 1993). Because a few males gain a disproportionately Human mortality patterns and sex differences high number of matings, male mating in mortality rates have been influenced by competition is a potent selection force (Betzig, numerous historical factors. In about the past 1986). The degree of physical sexual 10,000 years, the rise of agriculture and dimorphism is directly related to the level of domestication of animals led to higher male mating competition (see Bribiescas, 2006), mortality rates from infectious diseases, and human females are on average 80% as large facilitated by increasing population size and as males (Clutton‐Brock, 1985). density, increased mobility, and the greater prevalence of pathogens transferred from other Proximate Causation animals (Diamond, 1997). In the last two Sexual selection has resulted in a variety of centuries, modern public health and sanitation human sex differences in psychology and measures, vaccination, antibiotics, and other behavioral tendencies related to mortality, features of scientific medicine have resulted in a including the greater male tendencies for risk‐ major epidemiological transition from mortality taking, competitiveness, aggression, and mainly caused by infection, other acute diseases sensitivity to position in social hierarchies and pregnancy and childbirth, to mortality (Cronin, 1991). This accounts for many of the resulting mainly from chronic diseases related immediate causal mechanisms within and to lifestyle and aging in technologically outside the individual for sex divergent advanced nations (Lopez, 1998). As the massive mortality patterns. Mating competition among and relatively sex indiscriminate death rates men includes potentially lethal violence in from infection decline, and as deaths from conflicts both within and between groups childbirth decrease, mortality discrepancies (Chagnon, 1988). Archeological evidence arising from behavioral causes become indicates that a much higher proportion of proportionately much more prominent (Kruger individuals died from violent acts than those in & Nesse, 2004). Technological innovations in modern societies (e.g., Schulting, 2006). transportation, weaponry, and manufacturing Foraging societies frequently feature have exacerbated sex differences in mortality opportunistic raiding and ambushes, which are from risky behaviors. The proportionate more common than organized formal battles contribution of causes of death mediated by (Buss, 1995; Ember, 1978; Keeley, 1996). These health related behaviors, such as smoking and conflicts emerge from motives to retaliate for poor diet, has also increased sex differences in

Human Ethology Bulletin, 26(2), 2011 15

mortality in middle and late adulthood (Kruger mutations on the X chromosome because there & Nesse, 2004). In many countries, this are less likely to have the normal counterpart secondary peak reached its highest levels a few (Smith & Warner, 1989). Whereas female sex decades ago and is gradually declining (Kruger hormones appear to have beneficial & Nesse, 2004), perhaps from historical physiological influences (Lawlor, Ebrahim, & reductions sex differences in rates of health Smith, 2001), testosterone has a detrimental impacting risky behaviors such as tobacco impact on many somatic systems (Folstad & smoking. Overall, the discrepancy between Karter, 1992; Hazzard, 1990). Male secondary male and female mortality rates steadily sexual characteristics are dependent on increased in developed nations across the testosterone levels; this dynamic represents a twentieth century (Kruger & Nesse, 2004; trade‐off between reproductive and somatic Lopez, 1998; Zhang, Sasaki, & Kesteloot, 1995). investment. Males are more vulnerable to infection and parasites because of the We consider the ratio of male to female interference of testosterone with immunological mortality rates to be a useful indicator systems (Hazzard, 1990; Kraemer, 2000; Moore reflecting the interaction of evolved strategies & Wilson, 2002). High ranking chimpanzee and socio‐environmental conditions. Thus, we males have both higher testosterone levels and utilize the Male:Female Mortality Ratio (M:F increased parasite burden. MR) in our descriptive results, as it efficiently indicates population characteristics such as the (Muehlenbein & Watts, 2010). Male New severity of male‐male competition, Zealand fur seals who facilitate mating by environmental uncertainty, and the degree of establishing territories also have both higher variance in resources and social status. In the testosterone levels and increased parasite contemporary USA, cardiovascular disease burden compared to non‐territorial males; accounts for the single greatest proportion territorial males show both more aggressive (26%) of excess male life years lost beyond behavior with other males and more sexual female mortality rates. External causes account behavior with females in this moderately for 35% of excess male life years lost, including polygynous species (Negro, Caudron, Dubois, non‐automobile accidents (10%), suicide and Delahaut, & Gemmell, 2010). Larger male body auto‐accidents (both 9%), and homicide (7%). size also poses greater physiological costs Malignant neoplasms (cancer) account for 8%, (Owens, 2002). Increased dietary fat liver disease and cirrhosis 3%, congenital consumption has led to epidemic abnormalities 2%, and cerebrovascular disease cardiovascular disease in Western Nations in (stroke), pneumonia & influenza, and diabetes recent decades. This has disproportionately mellitus each account for 1% (Kruger, & Nesse, affected men in part because they are more 2004). The remainder of causes account for susceptible to atherosclerosis at any given level approximately 23% of excess male life years of fat intake (Lawlor, Ebrahim, & Smith, 2001). lost; however all individual causes account for Epidemiologists are beginning to recognize the less than 1%. evolutionary origins of riskier male behavior in Multiple levels of proximate factors influence their recommendations for health‐promoting mortality risk. Humans share the XX/XY sex‐ interventions (e.g., Nell, 2002). Men consume determination system with most other greater amounts of alcohol than women, . The Y‐chromosome in males is contributing to substantially higher mortality considerably shorter than the X chromosome from chronic liver disease and cirrhosis (Zhang, and contains an incomplete set of alleles. Thus, Sasaki, & Kesteloot, 1995). Men also smoke males are more susceptible to harmful more tobacco than women, though the sex 16 Human Ethology Bulletin, 26(2), 2011

differential in mortality for lung cancer and girls (Koot & Verhulst, 1991). Rough and stroke is declining because of decreases in male tumble play is three to six times more frequent smoking rates (Lopez, 1998) as well as increases in boys than girls, consisting of chasing, in female smoking rates (Pampel, 2002). Males capturing, wrestling, and restraining (DiPietro, die at higher rates from motor vehicle 1981). This form of play appears to be a accidents, even accounting for sex differences in mechanism for establishing social dominance, the number of miles driven (Jonah, 1986). Males something boys consider more important than also have much higher rates of death from girls do (Jarvinen & Nicholls, 1996). Male violent behaviors (Daly & Wilson, 1997; dominance hierarchies emerge at six years of Kraemer, 2000) and suicides (McClure, 2000). age and relative social status predicts social Occupational hazards increase mortality in rank nine years later (Weisfeld, 1999). disproportionately male professions (Hazzard, Sex differences in mortality from direct 1986). behavioral causes increase rapidly during Male tendencies for riskier behavioral patterns adolescence (Kruger & Nesse, 2004, 2006a), are ultimately a result of greater skew and corresponding to the activation of the variance in reproductive success compared to reproductive neuroendocrine system females. Wilson and Daly (1997) argue that this (Bribiescas, 2006). The steady rise in adrenal risk taking and discounting of future prospects androgens initiates the physical transition to could be a rational response to uncertainty in adulthood, marking the life history transition outcomes. They propose a convex‐upward from the somatic effort of building and association between proximate outcomes of maintaining the body towards reproductive risk‐taking (e.g., social status, resource control, effort. Male mating effort peaks in young mating opportunities) and reproductive success adulthood in modern societies, consistent with in unpredictable environments. Thus, these violent behavioral patterns and injuries from tendencies are maintained in the population accidents (See Figure 3). Men between ages 20 because they provided sufficient reproductive and 34 are most likely to commit and be the benefits to some proportion of individuals to victims of homicide (Daly & Wilson, 1988). be, even if they are also detrimental to many Young men may not yet have partners or individuals. offspring to invest in and thus can devote more effort to mating, and they may also be more Developmental Ontogeny attractive to females because they have not Human males are usually at greater risk of committed their resources (Hill & Kaplan 1999). mortality at all stages of life. Pregnancies with Among Ache foragers, younger men fathered male fetuses have higher miscarriage rates than more children through extra‐pair copulations those for females (MacDorman, Hoyert, Martin, than older men, who fathered more children Munson, & Hamilton, 2007). A male fetus will through long‐term relationships (Hill & typically extract more resources from the Hurtado 1996). mother to grow larger than females, leading to In Western industrialized countries, male greater risks of pre‐mature labor. Campbell testosterone levels peak just after age 20, (2005) argues that behavioral sex differences in declining gradually until more rapid drops childhood reflect preparation for the male after age 40. Marriage leads to declines in status contests of adolescence. Boys are more testosterone, though levels increase following assertive than girls at only a year and one divorce (Mazur & Michalek, 1998), reflecting month old (Goldberg & Lewis, 1969) and boys shifting life history. Men who grew up in between 2 and 4 are more aggressive and working‐class families during New Zealandʹs destructive towards people and objects than

Human Ethology Bulletin, 26(2), 2011 17

widespread unemployment of the 1980s and easy remarriage and most adult women had 1990s had low expectations for their futures and children by several different fathers. Organized made little effort to build job skills or integrate club fighting gave women opportunities to with mainstream society ‐ affiliating with anti‐ evaluate mates and new partnerships would social cohorts and engaging in frequent use of often begin after club fights (Hill & Hurtado, alcohol and other drugs. However, these men 1996). generally become more pro‐social, Cardiovascular disease was apparently absent economically productive, and family oriented in the forest dwelling Ache (Hill & Hurtado, after having children (Rouch, 2010). 1996). In industrialized countries, sex Life history patterns may differ somewhat in differences for behaviorally moderated internal non‐industrialized populations, where causes peak in mid to late adulthood, consistent testosterone does not decline as rapidly in later with the lag in the impact of health‐related adulthood (Ellison, Bribiescas, Bentley, behaviors on mortality (Kruger & Nesse, 2004, Campbell, Lipson, Panter‐Brick, & Hill, 2002). 2006a). Internal causes of death comprise both Among the Ache, for example, sex differences the largest source of mortality and the in mortality remain high throughout adulthood predominant proportion of life years lost from (Kruger & Nesse, 2006a). The forest dwelling excess male mortality in middle to late Ache had a flexible social system allowing for adulthood (See Figure 4).

Figure 3. Male:Female Mortality Ratios in The USA For External Causes During The Year 2000 (From Kruger & Nesse, 2004).

10 9 8 7 6 Automobile Accidents 5 Non-Automobile M:FMR 4 Accidents 3 Homicides 2 Suicides 1 0 1 1020304050607080 Age

Environmental conditions, broadly defined, mortality. Social norms for boys to be tough influence the magnitude of sex differences in and to not express emotions such as anxiety 18 Human Ethology Bulletin, 26(2), 2011

and shame may encourage risky male behavior 1997). In environments with high pathogen (Kindlon & Thompson, 1999; Kraemer, 2000). load, where parenting cannot improve Environmental uncertainty is associated with offspring survival, male strategies place more riskier behavioral strategies, as opportunities emphasis on mating effort including greater may be unpredictable and fleeting (Chisholm, risk taking and violence (Quinlan, 2007). Men 1999; Figueredo, Vásquez, Brumbach, Sefcek, with relatively low social status and resources Kirsner, & Jacobs, 2005; Roff, 1992; Stearns, may adopt risky strategies, having less to lose 1992). Neighborhood life expectancy predicts and facing the historical price of failure in homicide rates, controlling for the impact of evolutionary terms. In the United States, sex homicide (Wilson & Daly, 1997). Risk taking differences in mortality rates are higher among was higher among those who had lower those lower in income and education (Kruger & lifespan expectations and perceived future Nesse, 2006a). events as less predictable (Hill, Ross, & Low,

Figure 4. Male:Female Mortality Ratios in the USA for internal causes during the year 2000 (From Kruger & Nesse, 2004).

3.5

3

2.5 Malignant Neoplasms 2 Cardiovascular Diseases

M:FMR 1.5 Liver Disease and 1 Cirrhosis Cerebrovascular 0.5 Hypertension 0 1 1020304050607080 Age

The death rate from assaults is an order of Stockhammer, & Hood, 2002). The extent of magnitude more prevalent in Scottish routine neighborhood poverty explained over two‐ laborers than managers and professionals thirds of the variance in violent crime in one (Leyland & Dundas, 2010). Children growing Census Tract level study (Coulton, Korbin, Su, up in poverty are exposed to more violence & Chow, 1995). Across history, men who had (Sampson & Lauritsen, 1994), and this exposure dim prospects otherwise became warriors, is associated with individuals’ tendencies for adventurers, and explorers (Daly & Wilson, violent behavior (Salzinger, Feldman, 1988; Daly & Wilson, 2001).

Human Ethology Bulletin, 26(2), 2011 19

The degree of inequality in outcomes relatively short time scale. The variance and historically related to male reproductive skew in social status and resources in Eastern success will drive male competition and sex Europe rose sharply during the rapid transition differences in mortality. Neighborhood income market economies in the 1990s (United Nations inequality predicts homicide rates (Wilson & Development Program, 1998). Sex differences in Daly, 1997) and modern societies with greater mortality rates increased substantially for most degrees of economic inequality have of these nations, most prominently during early disproportionately higher levels of male adulthood, especially compared trends in mortality (Kruger, 2010). Consistent with Western European countries during this period patterns observed across species, the degree of (See Figure 5; Kruger & Nesse, 2007). During polygyny (indicating male reproductive the Croatian War of Independence in 1991‐1995, inequality) is also associated with the degree of evolved facultative adaptations responding to excess male mortality. Across nations, these adverse and unstable environments apparently two factors explain the majority of the variance led to riskier behavioral strategies in the civilian in sex differences in mortality rates (Kruger, population. Sex differences in non‐war related 2010). In addition, a relative population surplus violence and accidents peaked one year after of men increases mortality risk for men, but not the military conflict climaxed in intensity and women (Jin, Elwert, Freese, & Christakis, 2010). the non‐war male homicide rate was considerably higher for several years following Changes in environmental conditions the conflict compared to before (Kruger & associated with the intensity of male mating Nesse, 2006b). competition can influence sex differences on a

Figure 5. Male: Female Mortality Ratios across the Eastern European Economic Transition.

Note: Pre‐Transition 1985‐89, Transition 1990‐94, Post‐Transition 1995‐1999 (From Kruger & Nesse, 2007). 20 Human Ethology Bulletin, 26(2), 2011

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