This article is a contribution to a solution of the problem of how cooperation emerged in human social evolution. Contrary to models based on evolutionary game theory, the model presented here can provide a potential explanation of the emergence of cooperation and, at the same time, of group living. On the basis of assumptions with regard to individual (cognitive) capacities and ecological conditions, a dynamic object-oriented simulation model (the social evolution model [SEM]) is constructed to investigate the viability of social and asocial strategies of giving and requesting support. In this article, the SEM is used to examine whether social strategies with a “prefer-old-helping-partners” trait are viable in competition with asocial (cheating) strategies. It is found that social strategies take over small populations if their proportion is not too small and if conditions are harsh. In larger populations and if their proportions are not too small, they are able to prevent a takeover by the asocial strategies. In the discussion, we touch upon the implications of the SEM for the controversial issue of group altruism.
Men following quality and quantity strategies (pair bond with paternal investment/short-term sexual bonds) should have different, self-serving moral codes. If so, the different strategists should rate dating behaviors differently on ethical (honest and exploitative) and usage (by quality and quantity courters) scales. Quality strategists, who use honest advertisement, should promote their honest behavior by sharp distinctions between what is honest and exploitative and between what men like themselves and others (quantity strategists) do. Quantity strategists, who may exploit (e.g., verbal or physical coercion), should blur these distinctions. Their interests are served by the belief that all men are alike and not morally distinguishable. The companion study obtained men's ratings of quality-strategy behaviors (honest) and quantity-strategy behaviors (exploitative) on ethical and usage scales. Correlations were obtained between those ratings and the same men's scores on bipolar dimensions distinguishing quality from quantity strategists: sexual history, adult characteristics associated with female mate preference, and certain childhood experiences. The correlations supported the hypotheses with two exceptions. First, socioeconomic status and endorsement of a foraging tactic (leave if sexual relations do not start quickly) predicted ratings for quality-strategy behaviors, but did not predict ratings for quantity-strategy behaviors. Sexual history items and childhood experiences related to perceptions of relationships predicted only the ratings for quantity-strategy behaviors. Second, ratings of the lack of honesty in exploitative behavior and its lack of usage by quality courters did not distinguish the strategists. Three conclusions followed. One, there are two kinds of quantity strategists: commodifiers who trade resources for sex and predators who exploit. Two, quantity strategists are mixed strategists while some men follow only a quality strategy. Three, quantity strategists deceive themselves about the exploitative character of their behavior. The data fit evolutionary analyses of human morality and, with a few exceptions, current views of contextual factors governing adoption of different reproductive strategies.
The article introduces and elaborates the hypothesis of carrier features, characteristics which in females are attractive to males as mate-choice cues. Female carrier features increase paternal resemblance and are ultimately attractive because they help pair-bonded males distinguish genetic offspring from those conceived by mates in extra-pair copulations. The proposed kin recognition mechanism, whether culturally evolved or innate, facilitates discriminatory paternal investment, and hence male fitness. Carrier features would be attractive to males in monogamous species where paternal investment is high, and cuckoldry represents a significant risk to male fitness. Logical space exists for male sender features, which tend to be expressed in offspring regardless of female characteristics. Conflict of genetic interests between the sexes should favor the evolution of carrier, rather than sender, features in both sexes. The argument centers on humans, for whom candidate carrier features are discussed with regard to physiognomy, behavior, recessive traits, and body odor. Criticisms are discussed, and testable predictions enumerated.
A stochastic dynamic programming model is presented that supports and extends work on the reproductive performance of the !Kung Bushmen (Lee 1972; Blurton Jones and Sibly 1978; Blurton Jones 1986), proposing that !Kung women and their reproductive systems may be maximizing reproductive success, The stochastic dynamic programming approach allows the construction of a whole-life model where the physical/environmental constraints along with the uncertainty about future events !Kung women face when making reproductive choices can be explicitly built in, The model makes quantitative predictions for the optimal reproductive strategy assuming !Kung women are maximizing expected lifetime reproduction (ELR) given the physical parameters of !Kung life,The model relies on data gathered from the works cited above and some considerations from simple probability theory. The model predictions for optimal birth spacing match the !Kung reproductive data very well and support earlier findings (Blurton Jones and Sibly; Blurton Jones 1986), The utility of the dynamic modeling approach is illustrated when the effects of varying certain model parameters are investigated,By including the effect of the mother's mortality, which was not Included in the Blurton Jones and Sibly (1978) analysis, the model allows for further exploration of the application of an adaptive approach to human reproductive performance, By adding some considerations about the risks of childbirth for the mother the model not only predicts optimal birth spacing, which is site specific, but also predicts the optimal time for a woman to begin and cease having children, These predictions coincide with menarche and menopause and shed light on their possible adaptive value.
Since a man’s reproductive success depends on his ability to outcompete other men, male competitiveness may be expected to have been exposed to strong selective pressure throughout human history. Accordingly, the relatively low level of physical violence observed between men has been viewed as a puzzle. What could have limited the eagerness of men to out-compete each other? I study the evolution of male competitiveness in a model where men compete for both reproductive and productive resources. I show that high levels of male competitiveness are then consistent with evolution by natural selection if (a) the ecology is generous enough for men to supply little or no food to their children, (b) competing is not too costly in terms of productive resources, and (c) relatedness among males is low enough. While the main analysis takes women to passively accept the husband that emerges from the male-male competition, the results are qualitatively robust to allowing for female mate choice following the male-male competition game. Possible implications for our understanding of the evolution of marriage systems are discussed.
According to the mate deprivation hypothesis of sexual coercion, males are more likely to use sexually coercive tactics if they are disadvantaged in gaining access to desirable mates. This hypothesis was tested in a sample of 156 young, heterosexual, mostly single men enrolled in a Canadian university. Differential access to mates was indexed by self-perceived mating success, self-reported sexual history, and relative earning potential. Sexual coercion was assessed using the Koss's sexual experiences survey. Results did not support the hypothesis: men who identified themselves as sexually coercive tended to have higher self-perceived mating success, had significantly more extensive sexual histories, and did not report lower relative earning potential. Coercive men reported a greater preference for partner variety and casual sex. Sexual strategy theory is used to propose two alternative models of sexual coercion.
Maximizing reproductive success involves having as many children as possible that can themselves reproduce successfully, Thus, when Gabbra parents decide to have another baby, they must trade off the probability that they will be able to afford to raise the child and marry it off successfully when it reaches maturity against the risk that feeding and raising that child would diminish the family herd, harming the marriage prospects of other children and possibly even leading to household destitution, Here I use a dynamic, state-dependent optimality model to analyze this trade-off, The decision to have another baby depends on household wealth and the number of children they already have, Parents should not necessarily reproduce at the maximum rate to maximize reproductive success, and the costs of marrying off a child have a large impact on the optimal family size, In the Gabbra, the cost of marrying off boys greatly exceeds the cost of marrying off girls, An analysis of demographic data from Gabbra households with a living husband and a first wife that had reached menopause show that probability of remarriage is strongly dependent on the number of children the first wife had, Number of sons has a much greater influence than number of daughters on the probability of a second marriage, as predicted by the model, Men are attempting to create the optimal family.
This research considers biasing effects on the expression of moral intuitions. Participants in Study 1 were asked to resolve some hypothetical moral dilemmas that involved the death of one or another set of individuals. For half of the participants, the problems were phrased using a Kill wording and for the other half a Save wording, although the outcomes were identical in each case. In Study 2, framing effects were produced by posing dilemma problems in different orders and in different contexts. In Study 1, the Kill-Save wording difference strongly influenced the resolution of the problems. In Study 2, if the problems involved a single kind of dilemma, the order in which the dilemmas were presented affected the pattern of response, whereas order had no major effect for another two series using different dilemmas. Thus, there were framing effects produced by differences in wording and order that could influence the decisions people make when presented with dilemmas, but the effects were not always large nor did they always appear. The presence and strength of the effects seem to depend on a variety of psychological factors that the problem sets activate. These findings are considered within the perspective of the evolution of cognitive strategies.
Both male facial hair and male pattern baldness are genetically based, suggesting that they contributed to fitness. The multiple fitness model provides an evolutionary interpretation of the social perception of male pattern baldness and beardedness in terms of the multidimensional meaning of physical maturational stages. Male facial beardedness is associated with the sexual maturation stage and is hypothesized to signal aggressive dominance. Male pattern baldness, by contrast, is associated with the next stage of physical maturation, termed senescence. Pattern baldness may signal social maturity, a non-threatening form of dominance associated with wisdom and nurturance. We tested these hypotheses on social perceptions using manipulated male facial stimuli. We presented faces with three levels of cranial hair, including full, receding, and bald, and two levels of facial hair, beard with moustache and clean shaven. Consistent with the model, a decrease in the amount of cranial hair was associated with increased perceptions of social maturity, appeasement, and age, and decreased perceptions of attractiveness and aggressiveness. Targets with facial hair were perceived as more aggressive, less appeasing, less attractive, older, and lower on social maturity than clean shaven faces.
Human males may adopt the “quality” strategy, a long-term pair bond with considerable paternal investment, or the “quantity” reproductive strategy, short-term pair bonds with little paternal investment. We hypothesized that (1) the two strategies require different courtship tactics, which can be derived from their different goals, and (2) the behavior used by quality courters is perceived as honest while the quantity strategist is often exploitative. Act nominations of 79 subjects and the investigators generated a set of 71 dating behaviors. Sixty-four other subjects classified each behavior by the theoretically derived tactics. Fifty-four males rated the likelihood of usage of each behavior by a man interested in marriage (quality courter) and by men interested in sexual relationships (quantity courters) who typically deceive, manipulate, or coerce women. Fifty-three other males rated each behavior on ethical scales of honesty, deception, manipulation, and coercion. Both kinds of ratings indicated that (1) tactics of quality courtship involve honest advertisement through mutual assessment, resource expenditure, and a delay in sexual relations, and (2) tactics of quantity courtship involve indirect or direct threats, psychological pressure, and talking about sex. Ethical ratings and the range of behaviors likely to be used by quality and quantity courters confirmed the hypothesis about ethical perceptions of the two strategies and suggested that quantity courters are opportunistic as well as exploitative.
People everywhere attend to cues that convey information about social norms and try to comply with norms they believe are in force. In another article, we hypothesized that norm compliance serves a signaling function, and we reported that violations of everyday minor social norms cause observers to make invidious attributions that might decrease violators' fitness, if observers and violators were socially interacting (Wenegrat et al. 1996). A manipulation that increased the salience of such norms increased the adverse effects of norm violations. Many social norms are associated with groups and hence become more salient in situations that call attention to group membership. We performed experiments in which subjects watched videotapes of models violating such a norm in a setting that called attention to group membership. Subjects then rated those models on dimensions that would be relevant to the model's fitness, if subjects and models were socially interacting, and they also expressed their preferences regarding possible future interactions with the models. Violations of the group norm significantly altered fitness-relevant ratings and also preferences concerning future interactions. The results are consistent with the hypothesis that compliance with various social norms serves an important signaling function.
A central medical ethical concern is distributive justice, which may be framed as a problem in valuing identified lives versus statistical lives. Framing the issue in this way is important for two reasons. First, the growth of medical costs has been fueled and will continue to be fueled primarily by the growth of medical technology focused intensively, and often with little benefit for cost, on the care of identified lives. Second, there is some evidence that less expensive primary care, as opposed to high-tech medicine, is positively correlated with improved life expectancy, decreased infant and neonatal mortality, and fewer cases of low birth weight. However, shifting resources from high-tech medicine to primary care will be difficult because people find it psychologically painful to deny care to identified lives. People value identified lives more than statistical lives because we are influenced by certain cognitive preferences inherent to human nature. Natural selection has primed these cognitive preferences. There are no easy solutions to the profound problems facing healthcare systems. However, evolutionary insights can help us understand these problems and could productively inform attempts to promote primary care as opposed to high-tech medicine, thereby improving benefit for cost and enhancing social welfare.
There is a strong correlation between marriage system and wealth inheritance pattern across societies (Hartung 1982); as the degree of polygyny increases, so too does the degree of male bias in inheritance, In this paper, we reevaluate this pattern using a new technique in cross-cultural analyses that effectively controls for the nonindependence of cultures (Galton's problem) through the identification of independent instances of cultural change (Mace and Pagel 1994), First, we produce cultural phylogenetic trees for the societies under study, from phylogenies previously constructed on the basis of linguistic similarity (Ruhlen 1987). Then, following standard methods for the analysis of discrete characters on phylogenetic trees, we use parsimony to determine the ancestral condition of both marriage and inheritance, and subsequently tally the number of independent instances of cultural change in each trait. The results show that transitions to polygyny are much more commonly associated with male-biased inheritance than are transitions to monogamy across human societies in our sample, They illustrate how the degree of change in the evolution of these traits differs considerably between divergent cultural groups, The advantages of this technique are discussed.
Archer (this issue) contends that seduction by homosexual pedophiles is largely a result of media exaggeration and that xenophobia explains the data I reported on attitudes toward homosexuals (Gallup 1995), However, a cursory review of the evidence shows that the incidence of child molestation by homosexual males is much higher than Archer implies, and when the specific findings on attitudes are considered, xenophobia fails to provide an adequate account of the way people react to homosexuals.
This study tested specific predictions of risk preference in human choice derived from evolutionary hypotheses. The overall choice pattern revealed that subjects receiving a life-death decision problem described in a family context favored a risky probabilistic outcome over a statistically equivalent deterministic outcome. As predicted, the degree of such risk proneness varied as a function of sociobiologically important variables: the subject's age, their perspective, and the age cues about the hypothetical relatives saved in the deterministic outcome. Compared to young subjects, middle-aged subjects were much more prone to the deterministic outcome when it implied saving their younger family members but were extremely risk-seeking in favor of the probabilistic outcome when the deterministic choice resulted in the survival of older relatives. In contrast, the young subjects equally valued the younger and older hypothetical relatives and indistinguishably favored the probabilistic outcome under both saving-young and saving-old conditions. However, by changing the perspective of the young subjects from their own family to someone else's family, the saving-young deterministic outcome became more attractive than the saving-old deterministic outcome, resulting in differentiated risk-preference patterns. These results indicate an evolutionary origin of human reasoning and decision mechanisms that are sensitive to the biological characteristics of both decision makers and decision recipients.
Under the guise of a test-retest reliability study, students were asked to rate the attractiveness of photo reproductions of Caucasian males. Each of the photo reproductions was presented with a fictional descriptive sentence giving information on the depicted individual's social status (high or low) and character (history of cheating, irrelevant information, or history of trustworthiness). A week later subjects again rated photos—half repeated and half new—this time, without descriptions. Subjects were asked to report which of the photos they remembered from the previous week. Responses were analyzed in a 2×3×2 factorial design, with the third factor being sex of respondent. The predicted bias—that subjects would preferentially recognize faces initially presented as those of cheaters—was confirmed. There were also two significant interations: (1) the bias was mitigated when the face was also presented as a person of high status; and (2) the bias was stronger for males than for females. The results support the idea that we have evolved highly selective attention and storage mechanisms for processing social information, and that both character (cheating potential) and status are important features in the engagement of these mechanisms.
Based on the hypothesis that unobtrusively measured viewing time reflects sexual interest, it was predicted that viewing times should correlate with ratings of sexual attractiveness and with phallometrically measured age and gender preferences. Four additional predictions were derived from the Symons (1979) evolutionary theory of human mate preferences: (1) male and female subjects should view slides of young adults of the opposite sex longest and adults of the same sex and prepubescent children of both sexes the shortest, (2) the correlation between viewing time and sexual attractiveness ratings should be higher among males than females (3) males should look at slides of pubescent females longer than females look at slides of pubescent males, and (4) males should look longer at adult females than females look at adult males. Two studies involving 24 heterosexual females and 58 heterosexual males provided statistically significant support for all predictions except the last one.
Since Salk's first report (1960), many studies have confirmed a left-side bias in infant-holding among women. However, the present field observations in Madagascar show that 64% of 906 women and 73% of 231 men held their child on the right side of the body while standing or walking in a variety of public places. This right-side holding preference was seen in all of the ethnic groups observed. Moreover, the field observations were confirmed by the results of interviews with 67 women and 47 men. Possible explanations for the present findings are discussed.
Patterns of marriage, divorce, remarriage, and redivorce were examined in several representative Western cultures through survey questions and archival data to test the hypothesis that marriage and divorce can be understood as expressions of underlying gender-specific, fitness maximization strategies. Differences between males and females were found for the relationship between age and patterns of both marriage and divorce, with females being far more likely at almost all ages to initiate divorce proceedings than males. Once divorced, however, formerly married females were less likely to remarry than formerly married males. The presence of children from a prior marriage had the effect of further decreasing the likelihood of remarriage for females, but not for males. Formerly married males without children tended to remarry females who had never been married, whereas just the opposite was true for divorced males with children. Consistent with our view of marriage as a reproductive contract, the absence of children was not only conducive to divorce and remarriage, but appeared to increase the likelihood of redivorce as well.
Fluctuating asymmetry (FA) is small random deviations from perfect bilateral symmetry that are thought to accumulate during development. FA is therefore a measure of one component of fitness, that is, developmental stability. This work is not concerned with permanent between-individual differences in asymmetries but rather with temporary within-individual changes in asymmetry that are related to the menstrual cycle (cyclical asymmetry, CA). We present evidence from studies of non-sexually selected traits (ear and digit size) and a sexually selected trait (breast size) that, in characters made up wholly or in part of soft tissue, CA varies across the menstrual cycle in women. It is highest at the beginning and end of the cycle, when women are generally infertile, and low in mid-cycle, when fertility is highest. Furthermore in mid-cycle there is an indication of a transitory (24-hour) increase in CA followed by a substantial decrease, which may indicate ovulation. Temporal changes in CA could therefore be used by males to indicate a female's position in the cycle. We discuss these findings in relation to (1) our understanding of the evolution of human mating systems, (2) the practical implications of these data in the treatment of infertility and to facilitate contraception, and (3) their relevance to exercise and dieting as a means to minimize across-cycle increases in asymmetry.
