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This study aims to investigate assortative mating based on mate value from male perspective. Male participants (132 Brazilian and 106 American) evaluated hypothetical "stimulus" males described in terms of physical attractiveness, social skills, and social status (each varied in high or low levels). Participants rated each stimulus and each stimulus' preferred mating partner on nine traits. The results showed that (1) positive assortative mating was expected in romantic relationships; (2) the stimulus ratings did not vary independently, suggesting that mate value is the result of the interaction of the characteristics of individuals; and (3) that participants expected physically attractive and healthier female partners to pair with high-status male stimuli. The American and Brazilian mating expectations were similar, minor differences indicate that Brazilian participants considered men with high levels of social skills to be more ambitious and intelligent; American participants expected men of high status to be healthier; Brazilians expect men of high status to have more attractive faces, while Americans expected these men to possess more attractive bodies; and Brazilian participants assigned more attractive bodies to men of lower status. These differences reflect the influence of economic and cultural factors on the local environment. The study contributes to the understanding of the construction of market value and reveals that male expectations are in line with human mating preferences. The investigation of mating expectations can be a rich approach to investigate socio-cultural aspects that are related to mating in different cultures.

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OBJECTIVES: A core assumption of life history theory and the immunocompetence handicap hypothesis (ICHH) is that testosterone (T) upregulates energetic investment in mating effort at the expense of immunity. This tenet, along with observed positive relationships between estrogens and immunity, may contribute to the higher observed morbidity and mortality of males. In the present study, we examine the association between sex steroid hormones and mucosal immunity as well as sex differences in immunity in a rural Amazonian population of immune-challenged Bolivian adolescents. METHODS: Salivary steroid hormones (T [males only] and estradiol [E2 , females only]), Tsimane-specific age-standardized BMI z-scores, and salivary mucosal immunity (sIgA, secretory IgA) were measured in 89 adolescent males and females. RESULTS: Males had significantly higher sIgA levels than females, which may be due to the observed immune-endocrine associations found in the present study. Controlling for age and phenotypic condition, higher T significantly predicted higher sIgA; whereas higher E2 was associated with lower sIgA in females. CONCLUSIONS: Results stood in contrast to common interpretations of the ICHH, that is, that T should be inversely associated with immunity. Findings from the present study support the notion that the endocrine system likely affects immunity in a regulatory fashion, upregulating certain aspects of immunity while downregulating others. An important remaining question is the adaptive reason(s) for sex differences in endocrine-mediated immuno-redistribution.

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OBJECTIVES: Humans-and several other apes-exhibit a unique pattern of post-natal adrenal maturation; however, the causes and consequences of variation in adrenal development are not well understood. In this study, we examine developmental and age-related maturation of the adrenal gland (measured via dehydroepiandrosterone-sulfate [DHEA-S]) for potential life-history associations with growth and mucosal immunity in a rural population of immune-challenged Bolivian juveniles and adolescents. METHODS: Salivary DHEA-S, anthropometrics, and salivary mucosal immunity (secretory IgA [sIgA]) were measured in 171 males and females, aged 8-23. RESULTS: Males with greater energy (i.e. fat) stores showed higher DHEA-S levels. Controlling for age and energetic condition (to control for phenotypic correlation), higher DHEA-S was associated with higher mucosal immunity (sIgA) among both males and females. Higher DHEA-S levels were positively associated with growth (i.e. height and strength) in males. CONCLUSIONS: In accordance with predictions derived from life-history theory, males with higher energy stores secrete more adrenal androgens. This suggests that adrenal maturation is costly and subject to constraints; that is, only males with sufficient reserves will invest in accelerated adrenal maturation. Further, DHEA-S appears to have a measureable influence on immunocompetence in adolescent males and females; therefore, deficits in DHEA-S may have important consequences for health and maturation during this period. Adrenal maturation is an important, but understudied component of human growth and development.

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Facial width-to-height ratio (fWHR) has been proposed as a sexually dimorphic signal in humans that develops under the influence of pubertal testosterone (T); however, no studies have examined the association between fWHR and T during the phase in which facial growth is canalized--adolescence. In a sample of adolescent Tsimane males, we evaluate the relationship between T, known T-derived traits (i.e. strength and voice pitch), and craniofacial measurements. If fWHR variation derives from T's effect on craniofacial growth during adolescence, several predictions should be supported: 1) fWHR should increase with age as T increases, 2) fWHR should reflect adolescent T (rather than adult T per se), 3) fWHR should exhibit velocity changes during adolescence in parallel with the pubertal spurt in T, 4) fWHR should correlate with T after controlling for age and other potential confounds, and 5) fWHR should show strong associations with other T-derived traits. Only prediction 4 was observed. Additionally, we examined three alternative facial masculinity ratios: facial width/lower face height, cheekbone prominence, and facial width/full face height. In contrast to fWHR, all three alternative measures show a strong age-related trend and are associated with both T and T-dependent traits. Overall, our results question the status of fWHR as a sexually-selected signal of pubertal T and T-linked traits.

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Sex differences in reproductive strategy and the sexual division of labor resulted in selection for and maintenance of sexual dimorphism across a wide range of characteristics, including body size, hormonal physiology, behavior, and perhaps spatial abilities. In laboratory tasks among undergraduates there is a general male advantage for navigational and mental-rotation tasks, whereas studies find female advantage for remembering item locations in complex arrays and the locations of plant foods. Adaptive explanations of sex differences in these spatial abilities have focused on patterns of differential mate search and routine participation in distinct subsistence behaviors. The few studies to date of spatial ability in nonindustrial populations practicing subsistence lifestyles, or across a wider age range, find inconsistent results. Here we examine sex- and age-based variation in one kind of spatial ability related to navigation, dead-reckoning, among Tsimane forager horticulturalists living in lowland Bolivia. Seventy-three participants (38 male) aged 6-82 years pointed a handheld global positioning system (GPS) unit toward the two nearest communities and the more distant market town. We find no evidence of sex differences in dead reckoning (p = 0.47), nor do we find any evidence of age-related decline in dead-reckoning accuracy (p = 0.28). Participants were significantly more accurate at pointing toward the market town than toward the two nearest villages despite its being significantly farther away than the two nearest communities. Although Tsimane do show sexual dimorphism in foraging tasks, Tsimane women have extensive daily and lifetime travel, and the local environment lacks directional cues that typically enhance male navigation. This study raises the possibility that greater similarity in mobility patterns because of overlapping subsistence strategies and activities may result in convergence of some male and female navigation abilities.

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Sexual selection theory suggests that the sex with a higher potential reproductive rate will compete more strongly for access to mates. Stronger intra-sexual competition for mates may explain why males travel more extensively than females in many terrestrial vertebrates. A male-bias in lifetime distance travelled is a purported human universal, although this claim is based primarily on anecdotes. Following sexual maturity, motivation to travel outside the natal territory may vary over the life course for both sexes. Here, we test whether travel behaviour among Tsimane forager-horticulturalists is associated with shifting reproductive priorities across the lifespan. Using structured interviews, we find that sex differences in travel peak during adolescence when men and women are most intensively searching for mates. Among married adults, we find that greater offspring dependency load is associated with reduced travel among women, but not men. Married men are more likely to travel alone than women, but only to the nearest market town and not to other Tsimane villages. We conclude that men's and women's travel behaviour reflects differential gains from mate search and parenting across the life course.

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BACKGROUND: Age at menarche is often used to measure maturational tempo in girls. Unfortunately, no parallel marker exists for boys. It is suggested that voice change has a number of advantages as a marker of the timing and degree of male pubertal development. AIM: Traditional auxological methods are applied to voice change in order to compare differential development both between (males vs females; Tsimane vs North American; better vs worse condition) and within (voice vs height; fundamental frequency vs formant structure) populations. SUBJECTS AND METHODS: Fundamental and formant frequencies, as well as height and weight, were measured for 172 Tsimane males and females, aged 8-23. Participants were assigned to 'better' or 'worse' condition based on a median split of height-for-age and weight-for-age z-scores. RESULTS: Results support dramatic vocal changes in males. Peak voice change among Tsimane male adolescents occurs∼1 year later than in an age-matched North American sample. Achieved adult male voices are also higher in the Tsimane. Tsimane males in worse condition experience voice change more than 1 year later than Tsimane males in better condition. CONCLUSION: Voice change has a number of attractive features as a marker of male pubertal timing including its methodological and technical simplicity as well as its social salience to group members.

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Breast milk fatty acid (FA) composition varies greatly among individual women, including in percentages of the long-chain polyunsaturated FAs (LCPUFA) 20:4n-6 (arachidonic acid, AA) and 22:6n-3 (docosahexaenoic acid, DHA), which are important for infant neurological development. It has been suggested that owing to wide variation in milk LCPUFA and low DHA in Western diets, standards of milk FA composition should be derived from populations consuming traditional diets. We collected breast milk samples from Tsimane women at varying lactational stages (6-82 weeks). The Tsimane are an indigenous, natural fertility, subsistence-level population living in Amazonia Bolivia. Tsimane samples were matched by lactational stage to samples from a US milk bank, and analysed concurrently for FA composition by gas-liquid chromatography. We compared milk FA composition between Tsimane (n = 35) and US (n = 35) mothers, focusing on differences in LCPUFA percentages that may be due to population-typical dietary patterns. Per total FAs, the percentages of AA, DHA, total n-3 and total n-6 LCPUFA were significantly higher among Tsimane mothers. Mean percentages of 18:2n-6 (linoleic acid) and trans FAs were significantly higher among US mothers. Tsimane mothers' higher milk n-3 and n-6 LCPUFA percentages may be due to their regular consumption of wild game and freshwater fish, as well as comparatively lower intakes of processed foods and oils that may interfere with LCPUFA synthesis.

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Gaulin, McBurney, and Brakeman-Wartell (1997) found that college students reported both matrilateral and sex biases in the investment of aunts and uncles (aunts invested more than uncles). They interpreted the matrilateral bias as a consequence of paternity uncertainty. We replicated that study with Orthodox Jewish college students, selected because they come from a population we presume to have higher paternity certainty than the general population. The Orthodox sample also showed matrilateral and sex biases. Comparing the two data sets, the Orthodox sample reported more investment, and slightly less matrilateral and sex biases, but the differences were not statistically significant. We did find an interaction between sex of relative and group membership, resulting from greater investment by Orthodox uncles. We interpret the results as reflecting the operation of a facultative investment mechanism whose upper limit is tuned to the maximum levels of paternity certainty found in ancestral environments. Lack of a difference in matrilateral bias between groups may result from levels of paternity certainty near to, or above, that maximum in both groups.