Evolutionary theory predicts that humans should avoid incest because of the negative effects incest has on individual reproduction: production of defective offspring. Selection for the avoidance of close-kin mating has apparently resulted in a psychological mechanism that promotes voluntary incest avoidance. Most human societies are thought to have rules regulating incest. If incest is avoided, why are social rules constructed to regulate it? This target article suggests that incest rules do not exist primarily to regulate close-kin mating but to regulate (...) inbreeding between more distant kin and sexual relations between affinal relatives. Three evolutionary hypotheses about cousin marriage and affinal kin mating follow from this suggestion: Rules regulating mating between affinal kin are means of paternity protection. Cousin marriage is regulated because, if it occurs, it can concentrate wealth and power within families to the detriment of the powerful positions of rulers in stratified societies and the relatively equal social statuses of most men in egalitarian societies. Tests using the comparative method on a worldwide sample of 129 societies supported the three hypotheses. Two alternative anthropological hypotheses failed to be supported. (shrink)

Contemporary mate preferences can provide important clues to human reproductive history. Little is known about which characteristics people value in potential mates. Five predictions were made about sex differences in human mate preferences based on evolutionary conceptions of parental investment, sexual selection, human reproductive capacity, and sexual asymmetries regarding certainty of paternity versus maternity. The predictions centered on how each sex valued earning capacity, ambition— industriousness, youth, physical attractiveness, and chastity. Predictions were tested in data from 37 samples drawn from (...) 33 countries located on six continents and five islands. For 27 countries, demographic data on actual age at marriage provided a validity check on questionnaire data. Females were found to value cues toresource acquisitionin potential mates more highly than males. Characteristics signalingreproductive capacitywere valued more by males than by females. These sex differences may reflect different evolutionary selection pressures on human males and females; they provide powerful cross-cultural evidence of current sex differences in reproductive strategies. Discussion focuses on proximate mechanisms underlying mate preferences, consequences for human intrasexual competition, and the limitations of this study. (shrink)

In both biology and the human sciences, social groups are sometimes treated as adaptive units whose organization cannot be reduced to individual interactions. This group-level view is opposed by a more individualistic one that treats social organization as a byproduct of self-interest. According to biologists, group-level adaptations can evolve only by a process of natural selection at the group level. Most biologists rejected group selection as an important evolutionary force during the 1960s and 1970s but a positive literature began to (...) grow during the 1970s and is rapidly expanding today. We review this recent literature and its implications for human evolutionary biology. We show that the rejection of group selection was based on a misplaced emphasis on genes as "replicators" which is in fact irrelevant to the question of whether groups can be like individuals in their functional organization. The fundamental question is whether social groups and other higher-level entities can be "vehicles" of selection. When this elementary fact is recognized, group selection emerges as an important force in nature and what seem to be competing theories, such as kin selection and reciprocity, reappear as special cases of group selection. The result is a unified theory of natural selection that operates on a nested hierarchy of units. The vehicle-based theory makes it clear that group selection is an important force to consider in human evolution. Humans can facultatively span the full range from self-interested individuals to "organs" of group-level "organisms." Human behavior not only reflects the balance between levels of selection but it can also alter the balance through the construction of social structures that have the effect of reducing fitness differences within groups, concentrating natural selection (and functional organization) at the group level. These social structures and the cognitive abilities that produce them allow group selection to be important even among large groups of unrelated individuals. (shrink)

I have provided evidence that Geary's model does not explain male dominance in spatial abilities by sexual selection. The current literature concerning the relations of nonverbal IQ to testosterone, hand preference, and right- and left-hand skill, as well as the organizing effects of testosterone on cerebral lateralization during the perinatal period, does not support Geary's arguments.

From the perspective of evolutionary theory, we believe it makes more sense to view the sex differences in spatial cognition as being an evolutionary by-product of selection for optimal rates of fetal development. Geary does not convince us that his proposed selective factors operated with “sufficient precision, economy, and efficiency.” Moreover, the archaeological evidence does not support his proposed evolutionary scenario.

We challenge the notion that differences in spatial ability are the best or only explanation for observed sex differences in mathematical word problems. We suggest two ideas from the study of autism: sex differences in theory of mind and in central coherence.

The principles of sexual selection were used as an organizing framework for interpreting cross-national patterns of sex differences in mathematical abilities. Cross-national studies suggest that there are no sex differences in biologically primary mathematical abilities, that is, for those mathematical abilities that are found in all cultures as well as in nonhuman primates, and show moderate heritability estimates. Sex differences in several biologically secondary mathematical domains are found throughout the industrialized world. In particular, males consistently outperform females in the solving (...) of mathematical word problems and geometry. Sexual selection and any associated proximate mechanisms influence these sex differences in mathematical performance indirectly. First, sexual selection resulted in greater elaboration in males than in females of the neurocognitive systems that support navigation in three-dimensional space. Knowledge implicit in these systems reflects an understanding of basic Euclidean geometry, and may thus be one source of the male advantage in geometry. Males also use more readily than females these spatial systems in problem-solving situations, which provides them with an advantage in solving word problems and geometry. In addition, sex differences in social styles and interests, which also appear to be related in part to sexual selection, result in sex differences in engagement iii mathematics-related activities, thus further increasing the male advantage in certain mathematical domains. A model that integrates these biological influences with sociocultural influences on the sex differences in mathematical performance is presented in this article. (shrink)

The nonreproductive role of religious women in the European Middle Ages presents the ideal forum for the discussion of elite family strategies within a historical context. I apply the evolutionary concept of kin selection to this group of women in order to explain how a social formation in which religious women failed to reproduce benefited medieval noble lineages. After a brief review of the roles of noble women in the later Middle Ages, I identify two benefits that nonreproductive women provided (...) within a patrilineal inheritance system. First, spatial segregation and Christian ideology together served to curtail the production of offspring who could pose a threat to lineage interests. Second, cloistered noble women served as a strong political and economic bloc that could further lineage interests within a religious context. Finally, I discuss the evolutionary basis for the formation of groups of nonreproductive women. Using the foundation provided by animal behavioral studies, I apply the twin concepts of cooperative breeding and parental manipulation to noble lineages of the medieval period. (shrink)

Sex differences in behavior are most interesting when they are the result of inherent differences in the operational rules motivating behavior and not merely a reflection of differing life history experiences. American men and women exhibit a few differences in testamentary patterns of property allocation that appear to be due to inherently different rules of allocation. Even when analyses control for resources and surviving kin configurations, women distribute their property among a greater number of individual beneficiaries than do men. The (...) most striking differences in property allocation between men and women occur within the nuclear family and reflect differences in reproductive life span and the resulting reproductive conflicts between spouses that can endure beyond death. (shrink)

A common exhortation by conservationists suggests that we can solve ecological problems by returning to the attitudes of traditional societies: reverence for resources, and willingness to assume short-term individual costs for long-term, group-beneficial sustainable management. This paper uses the 186-society Standard Cross-Cultural Sample to examine resource attitudes and practices. Two main findings emerge: (1) resource practices are ecologically driven and do not appear to correlate with attitude (including sacred prohibition) and (2) the low ecological impact of many traditional societies results (...) not from conscious conservation efforts, but from various combinations of low population density, inefficient extraction technology, and lack of profitable markets for extracted resources. (shrink)

Menstrual taboos are nearly ubiquitous and assume parallel forms in geographically distant populations, yet their function has baffled researchers for decades. This paper proposes that menstrual taboos are anticuckoldry tactics. By signaling menstruation, they may advertise female reproductive status to husbands, affines, and other observers. Females may therefore have difficulty in obfuscating the timing of the onset of pregnancy. This may have three consequences: (a) males are better able to assess their probabilities of paternity and to direct their parental investment (...) toward genetic offspring; (b) adulterous pregnancies are more easily detected and penalized, enhancing sexual fidelity; and (c) males avoid marrying pregnant females by relying on menstruation as evidence of nonpregnancy. This hypothesis is tested with 29 months of field data on menstrual taboos among the Dogon of Mali. Key results include the following: (a) cuckoldry is a major Dogon concern, (b) menstrual huts advertise female reproductive status, (c) husbands impose the taboos upon their wives, (d) female defiance of the taboos is undetectable and probably rare, and (e) informants think that the taboos help husbands and patrilineages to avoid cuckoldry. Thus the anti-cuckoldry hypothesis provides helpful insight into the menstrual taboos of the Dogon and should be tested among other populations. (shrink)

Patterns of human kinship commonly involve preferential treatment of relatives based on lineal descent (lineages) rather than degree of genetic relatedness (kindreds), presenting a challenge for inclusive fitness theory. Here, we examine effects of lineage and kindred characteristics on reproductive success (RS) and number of grandchildren for 130 men and 124 women in a horticultural community on Dominica. Kindreds had little effect on fitness independently of lineage characteristics. Fitness increased with the number of lineal relatives residing in the community but (...) decreased beyond an apparently optimal lineage size, suggesting resource enhancement and competition among kin. Female-biased patrilineage sex ratio was positively associated with men’s fitness, while male-biased matrilineage sex ratio was positively associated with women’s fitness. Number of brothers in the community was negatively associated with men’s, but not women’s, fitness. Parents and number of sisters had no effect on either male or female reproduction; however, women with younger sisters had higher RS, suggesting benefits of kin support for childcare. In sum, imposed norms for lineage social organization may enhance lineal ancestors’ inclusive fitness at a cost to individual inclusive fitness. (shrink)

I argue that the magnitude and nature of sex differences in aggression, their development, causation, and variability, can be better explained by sexual selection than by the alternative biosocial version of social role theory. Thus, sex differences in physical aggression increase with the degree of risk, occur early in life, peak in young adulthood, and are likely to be mediated by greater male impulsiveness, and greater female fear of physical danger. Male variability in physical aggression is consistent with an alternative (...) life history perspective, and context-dependent variability with responses to reproductive competition, although some variability follows the internal and external influences of social roles. Other sex differences, in variance in reproductive output, threat displays, size and strength, maturation rates, and mortality and conception rates, all indicate that male aggression is part of a sexually selected adaptive complex. Physical aggression between partners can be explained using different evolutionary principles, arising from the conflicts of interest between males and females entering a reproductive alliance, combined with variability following differences in societal gender roles. In this case, social roles are particularly important since they enable both the relatively equality in physical aggression between partners from Western nations, and the considerable cross-national variability, to be explained. (shrink)

Both science and ethics are embedded in cultural traditions where truths are shared through education; both need competent critics educated within such traditions. Education in both ought to be directed although moral education demands levels of responsible agency that science education does not. Evolutionary science often carries an implicit or explicit understanding of who and what humans are, one which may not be coherent with the implicit or explicit human self‐understanding in moral education. The latter in turn may not be (...) coherent with classical human self‐understandings. Moral education may enlighten and elevate the human nature that has evolved biologically. (shrink)

Relatively short Dutch introduction to an evolutionary approach to morality. A synthesis is given of various models of moral evolution. Some remarks are made on a way to look at the evolution of a compatibilistic 'free will' and a model is given of a way in which the 'good' can be understood as the results of shared interests (which, of course, gives an incomplete model, but at the same time throws a lot of light on the way in which we (...) have to resolve ethical issues). (shrink)

Runaway social selection resulting from partner choice may have shaped aspects of human cooperation and complex sociality that are otherwise hard to account for. Social selection is the subtype of natural selection that results from the social behaviors of other individuals. Competition to be chosen as a social partner can, like competition to be chosen as a mate, result in runaway selection that shapes extreme traits. People prefer partners who display valuable resources and bestow them selectively on close partners. The (...) resulting phenotypic covariance between displays and preferences gives fitness advantages to both, creating runaway selection that could shape a whole suite of prosocial traits including altruism, moral capacities, empathy, and theory of mind. Even though they give a net fitness benefit, traits at the endpoint of runaway social selection can have substantial deleterious effects on other traits such as viability, ability to accumulate resources, or vulnerability to mental disorders. Social selection forces arising from self-interested partner choices may be an invisible hand that shaped capacities for commitment, altruism, and other prosocial capacities of the human social brain. (shrink)

This essay critiques dual-inheritance theory as presented in Peter Richerson and Robert Boyd's book Not by Genes Alone: How Culture Transformed Human Evolution (2005). The theory states that culture became prominent in human evolution because it allowed relatively rapid adaptation to changing environments by means of imitation. Imitating the behavior of other members of one's community produces adaptive behaviors more readily than either genetic evolution or individual learning. Imitation follows a number of patterns: imitating high-status individuals, imitating the most common (...) forms of behavior, imitating behaviors perceived to be the most effective solutions to various problems relevant to survival. This process combined with occasional innovations in behavior lead to a process of cultural evolution involving populations of cultural variants. Different local human populations were associated with different local populations of cultural variants, and both the human and the cultural populations evolved over time. Human evolution cannot be understood without taking into account these parallel processes of genetic and cultural evolution. Not by Genes Alone traces the implication of dual-inheritance theory for understanding human evolution and refers to various bodies of evidence relevant to the theory. (shrink)

Social and behavioral scientists - that is, students of human nature - nowadays hardly ever use the term ‘human nature’. This reticence reflects both a becoming modesty about the aims of their disciplines and a healthy skepticism about whether there is any one thing really worthy of the label ‘human nature’.

Although it has become increasingly evident that an adequate theory of obligation must rest on evolutionary biology and human ethology, attempts toward this end need to explore the full range of personal, cultural, and political obligations observed in our species. The new naturalism reveals the complexity of social behavior and the defects of reductionist models that oversimplify the foundations of human duties and rights. Ultimately, this approach suggest a return to the Aristotelian concept of natural justice.