Sexual size dimorphism is generally associated with sexual selection via agonistic male competition in nonhuman primates. These primate models play an important role in understanding the origins and evolution of human behavior. Human size dimorphism is often hypothesized to be associated with high rates of male violence and polygyny. This raises the question of whether human dimorphism and patterns of male violence are inherited from a common ancestor with chimpanzees or are uniquely derived. Here I review patterns of, and causal (...) models for, dimorphism in humans and other primates. While dimorphism in primates is associated with agonistic male mate competition, a variety of factors can affect male and female size, and thereby dimorphism. The causes of human sexual size dimorphism are uncertain, and could involve several non-mutually-exclusive mechanisms, such as mate competition, resource competition, intergroup violence, and female choice. A phylogenetic reconstruction of the evolution of dimorphism, including fossil hominins, indicates that the modern human condition is derived. This suggests that at least some behavioral similarities with Pan associated with dimorphism may have arisen independently, and not directly from a common ancestor. (shrink)

A large body of research links testosterone and cortisol to male-male competition. Yet, little work has explored acute steroid hormone responses to coalitional, physical competition during middle childhood. Here, we investigate testosterone, dehydroepiandrosterone, androstenedione, and cortisol release among ethnically Chinese boys in Hong Kong, aged 8–11 years, during a soccer match and an intrasquad soccer scrimmage, with 63 participants competing in both treatments. The soccer match and intrasquad soccer scrimmage represented out-group and in-group treatments, respectively. Results revealed that testosterone showed (...) no measurable change. DHEA increased during both treatments in the majority of participants and the degree of change had no relation to independent variables or covariate measures. Most boys experienced androstenedione increases during match play, but no significant differences during the intrasquad soccer scrimmage competitions. The magnitude of change differed significantly between treatments and was positively associated with age. These latter findings suggest boys’ androstenedione responses may be sensitive to competitor type. For most subjects, cortisol significantly increased during match play, decreased during the intrasquad soccer scrimmage, and differed significantly between treatments, suggesting each treatment promoted a different psychological state among competitors. Cortisol/DHEA molar ratio decreased during the intrasquad scrimmage, suggestive of a more relaxed mental state. These data shed new light on potential proximate mechanisms associated with coalitional competition among prepubescent boys, with relevance to adrenarche and life history theory. (shrink)

This paper investigates relationships between men’s testosterone and family life in a sample of approximately 350 Jamaican fathers of children 18–24 months of age. The study recognizes the role of testosterone as a proximate mechanism coordinating and reflecting male life history allocations within specific family and cultural contexts. A sample of Jamaican fathers and/or father figures reported to an assessment center for an interview based on a standardized questionnaire and provided a saliva sample for measuring testosterone level. Outcomes measured include (...) subject demographics such as age and relationship status as well as partnership quality and sexuality and paternal attitudes and behavior. The variation in these fathers’ relationship status was not associated with men’s testosterone. Too few stepfathers participated to enable a direct test of the prediction that stepfathers would have higher testosterone than biological fathers, although fathers who reported living with partners’ children did not have higher testosterone than fathers not reporting residing with a non-biological child. Fathers’ relationship quality was negatively related to their testosterone. Measures of paternal attitudes and behavior were not related to fathers’ testosterone. Consistent with previous ethnography, this sample of Jamaican fathers exhibited variable life history profiles, including residential status. We discuss why fathers’ relationship quality was found to be negatively related to their testosterone level, but other predictions were not upheld. (shrink)

This paper highlights the evolutionary biological epistemology in Freud psychoanalytic theory. The concepts of aggressive and sexual drives are fulcrum of the psychoanalytic epistemological system, concerning the motivational/emotional roots of mental functioning. These biological roots of mental functioning, especially with regard to aggressive drive, have gradually faded away from psychoanalytic epistemology, as we show in the paper. Currently, however, Neurosciences, and in particular Affective Neuroscience (Panksepp 1998), can contribute to increase the knowledge of the biological roots of human mental functioning. (...) The motivational/emotional systems studied by Affective Neuroscience can give a new epistemological foundation to the aggressive drive concept in psychoanalytic theory. Over the course of human evolution motivational/emotional systems have assumed the role of organizers of social relationships and also of mental functioning. In this regard, among the various types of aggression (ANGER in Panksepp taxonomy 1998), that we consider in our paper is inter-male aggression, also named Dominance motivational/emotional system, which regulates social interactions between sexually mature adults. This type of aggression acts in complementary connection with FEAR motivational/emotional system, that regulate Submissive behaviour and Social defeat, the latter one of the more important stressors. The interaction between aggressiion and FEAR motivational/emotional systems gives rise to Agonistic behaviour or Dominance/Submission motivational/emotional system, as we propose in our paper. There is now a large literature that identifies in the dynamic of Agonistic behaviour one of the main factors of mental illness. When social interactions activate the Agonistic behavior, the subject can perceive himself as "destined to victory" or "destined to defeat", activating either behaviours and emotions connected to the Involuntary Defeat Strategy or Involuntary Dominant Strategy, that we can find in many types of mental disorders, e.g. mood disorders or anxiety disorders. (shrink)

The papers in this volume present varying approaches to human aggression, each from an evolutionary perspective. The evolutionary studies of aggression collected here all pursue aspects of patterns of response to environmental circumstances and consider explicitly how those circumstances shape the costs and benefits of behaving aggressively. All the authors understand various aspects of aggression as evolved adaptations but none believe that this implies we are doomed to continued violence, but rather that variation in aggression has evolutionary roots. These papers (...) reveal several similarities between human and nonhuman aggression, including our response to physical strength as an indicator of fighting ability, testosterone response to competition, a sensitivity to paternity, and baseline features of intergroup aggression in foragers and chimps. There is also one paper tackling the phylogeny of these traits. The many differences between human and nonhuman aggression are also pursued here. Topics here include the impact of modern weapons and extremes of wealth and power on both the costs and benefits of fighting, and the scale to which coercion can promote aggression that acts against a fighter’s own interests. Also the implications of large-scale human sociality are discussed. (shrink)

Testosterone fluctuates in response to competitive social interactions, with the direction of change typically depending on factors such as contest outcome. Watching a competition may be sufficient to activate T among fans and others who are invested in the outcome. This study explores the change in T associated with vicarious experiences of competition among combat sport athletes viewing a teammate win or lose and assesses how individual differences in social identification with one’s team relates to these patterns of T reactivity. (...) Twenty-six male combat athletes completed a social identity questionnaire on a neutral day. Later, salivary samples were obtained before and after athletes viewed a video of a teammate engaged in a formal contest. T reactivity to viewing a teammate compete varied among participants in both the magnitude and direction of change, independent of contest outcome. Individual differences in cognitive centrality, a core feature of social identification, showed a strong positive relationship with T reactivity, particularly if their teammate won. Initial findings suggest that dominance-linked androgen responses associated with watching a teammate win a competition might depend on the belief that team membership is central to one’s own identity. These exploratory results in a small sample of combat athletes should be interpreted with caution. Uncovering the role of social group dynamics in influencing T responses to competition is particularly important in light of the evolutionary history of coalitional combat in humans. (shrink)

Benenson et al. postulate that human females evolved unique survival adaptations to facilitate maternal and grandmaternal care. This hypothesis is consistent with the broader hypothesis that female phenotypes are more ecologically optimal, but further evidence is needed to make a compelling case that sex differences in self-protection are not primarily the result of more intense sexual selection on males.

Independent of ecology, subsistence strategy, social complexity, or other aspects of socioecology, the altricial nature of young humans requires mothers to have help raising their offspring. What seems to be context-dependent, however, is who the helpers are, how they invest, and what the impacts of that investment are. In a series of papers that focus on parental and alloparental investment across five populations, this special issue of Human Nature uses evolutionary theory to examine how socioecological context influences modes of direct (...) parental investment among the boat-dwelling Shodagor of Bangladesh, modes of indirect paternal investment in the modern United States, and the biological outcome of paternal investment for men in Jamaica, as well as direct alloparental investment among village Bangladeshis and indirect alloparental investment in breastfeeding practices in the United States. (shrink)

In response to recent work on the nature of human aggression, and to shed light on the proximate, as opposed to ultimate, causes of tribal warfare, we present a record of events leading to a fatal Waorani raid on a family from another tribe, followed by a detailed first-person observation of the behavior of the raiders as they prepared themselves for war, and upon their return. We contrast this attack with other Waorani aggressions and speculate on evidence regarding their hormonal (...) underpinnings. On-the-ground ethnographic observations are examined in light of the neuroendocrinological literature. The evidence suggests a chain of causality in launching lethal violence, beginning with a perceived injury, culminating in a massacre, and terminating in rejoicing. Although no blood or saliva samples were taken at the time of this raid, the behaviors were consistent with a deliberate initiation of the hormonal cascade characterizing the “fight-or-flight” response, along with other hormonal changes. We conclude with observations on the stratified interrelationships of the cognitive, social, emotional, and neuroendocrinological causes of aggression leading to coalitional male homicide. (shrink)