Social biology最新文献

Human pair-bonding and paternal involvement have long been attributed to the need for biparental rearing of altricial offspring with extended periods of dependency. More recently, researchers have focused on the fertility benefits that pair-bonding offers men and have re-conceptualized paternal care as a stratagem designed to curry favor with the recipient children's mother. These models, however, fail to explain a number of puzzling empirical findings, namely the lack of a significant and robust effect of father-presence cross-culturally, despite what appears to be true paternal involvement. I argue that the record is better explained by conceptualizing reproduction within unions as a joint venture, in which men's contributions are not simply lumped onto women's invariant levels of parental investment, but one in which men's involvement allows wives to reduce their own allocations to parental investment and increase those to fertility (fertility model), thereby maximizing the production of the union, not simply child survivorship.

High testosterone levels reflect investment in male reproductive effort through the ability to produce and maintain muscle tissue and thus augment mate attraction and competitive ability. However, high testosterone levels can also compromise survivorship by increasing risk of prostate cancer, production of oxygen radicals, risk of injury due to hormonally-augmented behaviors such as aggression, violence and risk taking, reduced tissue and organ maintenance, negative energy balance from adipose tissue catabolism, and suppression of immune functions. Here, I briefly discuss how inter- and intra-individual variation in human male testosterone levels is likely an adaptive mechanism that facilitates the allocation of metabolic resources, particularly in response to injury, illness or otherwise immune activation. Maintaining low testosterone levels in resource-limited and/or high pathogen-risk environments may avoid some immunosuppression and suspend energetically-expensive anabolic functions. Augmenting testosterone levels in the presence of fertile and receptive mates, areas of high food resource availability, and low disease risk habitats will function to maximize lifetime reproductive success.

Usually face-to-face dominance contests between humans are nonviolent, even amiable. Most violence between young men occurs when dominance contests infrequently escalate beyond their usually bounds. Heightened testosterone is not a direct cause of male violence. Occasional outbreaks of violence occur for other reasons, and are often random outcomes. However testosterone does encourage (nonviolent) dominant behavior among young men, increasing the frequency of dominance contests, hence increasing the likelihood of violent outcomes. "Honor subcultures" such as are found in our inner cities place inordinate importance on the enhancement of personal reputations and the humiliation of losing face. This atmosphere of persistent challenge produces heightened testosterone in young black men of the inner city, raising the likelihood that they will engage in dominance competition, which in turn raises the likelihood of a violent, even fatal, outcome.

This study employs vital statistics data from Sweden, England, Wales, France, and Spain to examine male:female mortality differentials from 1750 through 2000 and their interrelationship with epidemiological transitions. Across all ages and time periods, the largest relative mortality disadvantages are to young adult men. When crisis mortality from the two world wars is removed, we show that the mortality in this young male age group is about two to three times the level of female mortality across all countries sampled. In addition, we show that the timing of this stabilization in male mortality disadvantages occurs during the last half of the twentieth century, at the same point that our measure of epidemiological change also stabilizes at a new low level. The findings are consistent with an interdisciplinary theoretical model that links social, technological and epidemiological changes that occurred through the first half of the 20th century with the unmasking and accentuation of mortality disadvantages among young adult men.