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Hypotheses regarding the selective pressures driving the threefold increase in the size of the hominid brain since Homo habilis include climatic conditions, ecological demands, and social competition. We provide a multivariate analysis that enables the simultaneous assessment of variables representing each of these potential selective forces. Data were collated for latitude, prevalence of harmful parasites, mean annual temperature, and variation in annual temperature for the location of 175 hominid crania dating from 1.9 million to 10 thousand years ago. We also (...) included a proxy for population density and two indexes of paleoclimatic variability for the time at which each cranium was discovered. Results revealed independent contributions of population density, variation in paleoclimate, and temperature variation to the prediction of change in hominid cranial capacity (CC). Although the effects of paleoclimatic variability and temperature variation provide support for climatic hypotheses, the proxy for population density predicted more unique variance in CC than all other variables. The pattern suggests multiple pressures drove hominid brain evolution and that the core selective force was social competition. (shrink)

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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 (i.e., those that emerge primarily in school) 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 (e.g., sex hormones) 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)

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A sample of 460 low-income women completed a mate preference questionnaire and surveys that assessed family background, life history, conscientiousness, sexual motives, self-ratings (e.g., looks), and current circumstances (e.g., income). A cluster analysis revealed two groups of women: women who reported a strong preference for looks and money in a short-term mate and commitment in a long-term mate, and women who reported smaller differences across mating context. Group differences were found in reported educational levels, family background, sexual development, number of (...) children, and motives for having sex. Implications for understanding individual differences in women’s mate-preference trade-offs are discussed. (shrink)

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We agree with Archer that human sex differences in aggression are well explained by sexual selection, but note that explanations of human behaviors are not logically mutually exclusive from explanations and therefore should not be framed as such. We discuss why this type of framing hinders the development of both social learning and evolutionary theories of human behavior.

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The relation between sex hormones and responses to partner infidelity was explored in two studies reported here. The first confirmed the standard sex difference in relationship jealousy, that males (n=133) are relatively more distressed by a partner’s sexual infidelity and females (n=159) by a partner’s emotional infidelity. The study also revealed that females using hormone-based birth control (n=61) tended more toward sexual jealousy than did other females, and reported more intense affective responses to partner infidelity (n=77). In study two, 47 (...) females were assessed four times across one month. Patterns of response to partner infidelity did not vary by week of menstrual cycle, but significant relations between salivary estradiol level and jealousy responses were obtained during the time of rising and high fertility risk. The implications, at least for females, are that any evolved psychological, affective, or behavioral dispositions regarding reproduction-related relationships are potentially moderated by estradiol, and that the use of synthetic hormones may disrupt this relation. (shrink)

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The male advantage in certain mathematical domains contributes to the difference in the numbers of males and females that enter math-intensive occupations, which in turn contributes to the sex difference in earnings. Understanding the nature and development of the sex difference in mathematical abilities is accordingly of social as well as scientific concern. A more complete understanding of the biological contributions to these differences can guide research on educational techniques that might someday produce more equal educational outcomes in mathematics and (...) other academic domains. (shrink)

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Mower questions some aspects of Geary's proposals regarding the nature of male-male and female-female relationships during human evolution and the implications for understanding the basis for same-sex friendships. The core of this proposal is reviewed and Mower's challenges to the core are addressed.

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Sexual selection traditionally involves male-male competition and female choice, but in some species, including humans, sexual selection can also involve female-female competition and male choice. The degree to which one aspect of sexual selection or another is manifest in human populations will be influenced by a host of social and ecological variables, including the operational sex ratio. These variables are discussed in connection with the relative contribution of sexual selection and the division of labor to the evolution of human sex (...) differences. (shrink)

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