Nicholas Pound

Testosterone responses to competition in men are related to facial masculinity

Relationships between androgens and the size of sexually dimorphic male traits have been demonstrated in several non-human species. It is often assumed that a similar relationship exists for human male faces, but clear evidence of an association between circulating testosterone levels and the size of masculine facial traits in adulthood is absent. Here we demonstrate that, after experimentally determined success in a competitive task, men with more a masculine facial structure show higher levels of circulating testosterone than men with less masculine faces. In participants randomly allocated to a ‘winning’ condition, testosterone was elevated relative to pre-task levels at 5 and 20 min post-task. In a control group of participants allocated to a ‘losing’ condition there were no significant differences between pre- and post-task testosterone. An index of facial masculinity based on the measurement of sexually dimorphic facial traits was not associated with pre-task (baseline) testosterone levels, but was associated with testosterone levels 5 and 20 min after success in the competitive task. These findings indicate that a mans facial structure may afford important information about the functioning of his endocrine system.

Does Masculinity Matter? The Contribution of Masculine Face Shape to Male Attractiveness in Humans

Background In many animals, exaggerated sex-typical male traits are preferred by females, and may be a signal of both past and current disease resistance. The proposal that the same is true in humans – i.e., that masculine men are immunocompetent and attractive – underpins a large literature on facial masculinity preferences. Recently, theoretical models have suggested that current condition may be a better index of mate value than past immunocompetence. This is particularly likely in populations where pathogenic fluctuation is fast relative to host life history. As life history is slow in humans, there is reason to expect that, among humans, condition-dependent traits might contribute more to attractiveness than relatively stable traits such as masculinity. To date, however, there has been little rigorous assessment of whether, in the presence of variation in other cues, masculinity predicts attractiveness or not. Methodology/Principal Findings The relationship between masculinity and attractiveness was assessed in two samples of male faces. Most previous research has assessed masculinity either with subjective ratings or with simple anatomical measures. Here, we used geometric morphometric techniques to assess facial masculinity, generating a morphological masculinity measure based on a discriminant function that correctly classified >96% faces as male or female. When assessed using this measure, there was no relationship between morphological masculinity and rated attractiveness. In contrast, skin colour – a fluctuating, condition-dependent cue – was a significant predictor of attractiveness. Conclusions/Significance These findings suggest that facial morphological masculinity may contribute less to mens attractiveness than previously assumed. Our results are consistent with the hypothesis that current condition is more relevant to male mate value than past disease resistance, and hence that temporally fluctuating traits (such as colour) contribute more to male attractiveness than stable cues of sexual dimorphism.

The Importance of Physical Strength to Human Males

Fighting ability, although recognized as fundamental to intrasexual competition in many nonhuman species, has received little attention as an explanatory variable in the social sciences. Multiple lines of evidence from archaeology, criminology, anthropology, physiology, and psychology suggest that fighting ability was a crucial aspect of intrasexual competition for ancestral human males, and this has contributed to the evolution of numerous physical and psychological sex differences. Because fighting ability was relevant to many domains of interaction, male psychology should have evolved such that a man’s attitudes and behavioral responses are calibrated according to his formidability. Data are reviewed showing that better fighters feel entitled to better outcomes, set lower thresholds for anger/aggression, have self-favoring political attitudes, and believe more in the utility of warfare. New data are presented showing that among Hollywood actors, those selected for their physical strength (i.e., action stars) are more likely to believe in the utility of warfare.

Fluctuating asymmetry and preferences for sex-typical bodily characteristics

Body size and shape seem to have been sexually selected in a variety of species, including humans, but little is known about what attractive bodies signal about underlying genotypic or phenotypic quality. A widely used indicator of phenotypic quality in evolutionary analyses is degree of symmetry (i.e., fluctuating asymmetry, FA) because it is a marker of developmental stability, which is defined as an organisms ability to develop toward an adaptive end-point despite perturbations during its ontogeny. Here we sought to establish whether attractive bodies signal low FA to observers, and, if so, which aspects of attractive bodies are most predictive of lower FA. We used a 3D optical body scanner to measure FA and to isolate size and shape characteristics in a sample of 77 individuals (40 males and 37 females). From the 3D body scan data, 360° videos were created that separated body shape from other aspects of visual appearance (e.g., skin color and facial features). These videos then were presented to 87 evaluators for attractiveness ratings. We found strong negative correlations between FA and bodily attractiveness in both sexes. Further, sex-typical body size and shape characteristics were rated as attractive and correlated negatively with FA. Finally, geometric morphometric analysis of joint configurations revealed that sex-typical joint configurations were associated with both perceived attractiveness and lower FA for male but not for female bodies. In sum, body size and shape seem to show evidence of sexual selection and indicate important information about the phenotypic quality of individuals.

Prudent sperm allocation in Norway rats, Rattus norvegicus: a mammalian model of adaptive ejaculate adjustment.

In species where there is postcopulatory competition between males in the form of sperm competition, theory predicts that males should show prudent sperm allocation. Specifically, males should adjust the number of sperm that they inseminate in response to variations in the risk and intensity of sperm competition. Some experimental evidence for nonmammalian species indicates that ejaculate expenditure can be dynamic and adjusted in accordance with sperm competition theory. However, most studies have not used within-subject experimental designs to demonstrate ejaculate adjustments by individual males, and there have been no unequivocal demonstrations of prudent sperm allocation in mammals. In the present study, copulatory ejaculates were collected from 12 male rats that each mated under two experimental conditions: alone in a cage with a female (monandrous) and (accompanied by a ‘rival’ male who observed the copulation from behind a perforated plastic screen (polyandrous). As predicted by sperm competition theory, males ejaculated significantly more sperm when copulating in the presence of a rival than when copulating alone. Furthermore, the magnitudes of these ejaculate adjustments were highly predictable and were relatively consistent across individual males.

Duration of sexual arousal predicts semen parameters for masturbatory ejaculates

A mans semen parameters may vary considerably from one specimen to the next, partly due to variability in the conditions under which the specimens are produced. In the present study, the relationship between the duration of preejaculatory sexual arousal and the quality of semen produced by masturbation was investigated. Twenty-five regular semen donors aged 22-44 provided a total of 292 semen specimens (median 11 per donor) over a period of 4 months. Each specimen was produced after a minimum of 3 days of ejaculatory abstinence and measures included the time taken to produce the specimen, ejaculate volume, sperm concentration, and percent motility. Linear regression revealed that, controlling for donor identity, there was a significant (t=2.13, P<.05) positive relationship between the time taken to produce a specimen and sperm concentration. We conclude that the duration of preejaculatory sexual arousal is an important predictor of ejaculate quality for specimens produced by masturbation and that variation in the duration of preejaculatory arousal may contribute to within-male fluctuations in semen parameters over time.

Psychological and physiological adaptations to sperm competition in humans

Postcopulatory competition between males, in the form of sperm competition, is a widespread phenomenon in many animal species. The extent to which sperm competition has been an important selective pressure during human evolution remains controversial, however. The authors review critically the evidence that human males and females have psychological, behavioral, and physiological adaptations that evolved in response to selection pressures associated with sperm competition. The authors consider, using evidence from contemporary societies, whether sperm competition is likely to have been a significant adaptive problem for ancestral humans and examine the evidence suggesting that human males have physiological and psychological mechanisms that allow for “prudent” sperm allocation in response to variations in the risk of sperm competition.

An Evolutionary Psychological Perspective on the Modulation of Competitive Confrontation and Risk-Taking

Publisher Summary This chapter discusses the variations in homicide as indicative of variations in competitive risk taking, interpreting prevalent conflict typologies and demographic patterns as reflections of evolved motivational and information processing mechanisms that function to regulate competitive inclinations and actions. Connections are then drawn to research on future discounting and impulsivity, on the effects of inequity on violence, and on the bidirectional influences between circulating testosterone levels and social experience. It argues that the Darwinian Theory, especially sexual selection theory, provides a framework that can both synthesize existing knowledge in these disparate domains and facilitate future discovery. Evolutionary psychology is the pursuit of psychological science with explicit consideration of the fact that the psyche is, like the body, a product of evolutionary processes.

Facial fluctuating asymmetry is not associated with childhood ill-health in a large British cohort study

The idea that symmetry in facial traits is associated with attractiveness because it reliably indicates good physiological health, particularly to potential sexual partners, has generated an extensive literature on the evolution of human mate choice. However, large-scale tests of this hypothesis using direct or longitudinal assessments of physiological health are lacking. Here, we investigate relationships between facial fluctuating asymmetry (FA) and detailed individual health histories in a sample (n = 4732) derived from a large longitudinal study (Avon Longitudinal Study of Parents and Children) in South West England. Facial FA was assessed using geometric morphometric analysis of facial landmark configurations derived from three-dimensional facial scans taken at 15 years of age. Facial FA was not associated with longitudinal measures of childhood health. However, there was a very small negative association between facial FA and IQ that remained significant after correcting for a positive allometric relationship between FA and face size. Overall, this study does not support the idea that facial symmetry acts as a reliable cue to physiological health. Consequently, if preferences for facial symmetry do represent an evolved adaptation, then they probably function not to provide marginal fitness benefits by choosing between relatively healthy individuals on the basis of small differences in FA, but rather evolved to motivate avoidance of markers of substantial developmental disturbance and significant pathology.

Sperm competition in humans

It is suggested that sperm competition (competition between the sperm from two or more males over the fertilization of ova) may account for the fact that sperm are so small and so numerous. In the entire absence of sperm competition, selection may favour an increase in sperm size so that the sperm contributes nutriment to the subsequent viability and success of the zygote. However, an extremely low incidence of sperm competition is adequate to prevent sperm size increasing. Vertebrate sperm should remain at minimal size provided that double matings (one female mated by two males) occur more often than about 4 times the ratio of sperm size:ovum size. The classical theory that sperm are small simply because of the difficulties of ensuring that ova do get fertilized may also explain sperm size, and both effects (sperm competition and ensuring fertilization) are likely to contribute to the stability of anisogamy. Large numbers of sperm can be produced because sperm are tiny and the optimal allocation of reproductive reserves to ejaculates is not trivially small even when double matings are rather rare. It is suggested that of its total mating effort, a male vertebrate should spend a fraction on sperm that is roughly equivalent to a quarter of the probability of double mating.