Graduate Student - Ph.D.

Anthropology

Center for the Integrative Study of Animal Behavior

Indiana University (Bloomington, IN)

Michael P. Muehlenbein

My interests lie in the study of hormonal processes and the neuroendocrine systems that contribute to human behavior, specifically female reproductive behavior.

Studies of intersexual competitive behaviors have typically focused on conspicuous intrasexual male/male competitions for access to mates, whereas studies of female/female competitions have focused on competition for resources. Although females may not be competing with each other for the chance to mate, that doesn’t mean they are not competing for sexual access to specific mates. According to sexual selection theory, females should compete for access to males whenever males vary in their ability to provide a limiting resource, such as genetic quality, that affects female fitness. Females are often seen as relatively identical in reproductive potential and in the realization of that potential, with resources for survival and the survival of offspring as the only limiting factors. This has sometimes led to a misunderstanding of how and what females compete for. Females require resources that can be used for future offspring and/or resources to support current offspring. These are important assets, more so than outright physical dominance or access to copulatory opportunities. In effect, females should compete not over access to copulatory events, but access to quality males for copulatory events. Males and females display markedly different strategies concerning aggressive behavior. Human males engage in direct aggression more frequently than females; with differences appearing in childhood. Females tend to prefer indirect forms of aggression. In humans, girls and women are more likely to compete through indirect forms of aggression such as shunning, stigmatizing, gossiping, and derogation. A possible form of intrasexual competition is for females to elevate the attractiveness of their own appearance when compared to that of their peers. This can be accomplished by making rivals appear to be less attractive to potential mates by derogating the rival’s physical attributes and stressing their own. Ovarian hormones mediate reproductive behaviors in females including mating, ovulation, pregnancy, birth, and lactation. Like testosterone, release of estrogen and progesterone is regulated by the hypothalamus via the secretion of gonadotrophic-releasing hormone. The hypothalamus-pituitary-ovarian axis constitutes a complex system that works to maintain the allostatic load of the reproductive system. Levels of estrogen, testosterone and progesterone fluctuate across the menstrual cycle in humans, as well as numerous other species. Studies have suggested that that human female sexual desires change across the menstrual cycle, with peaks in sexual desire occurring most commonly during the peri-ovulatory period. A few studies have shown significant relations between salivary estradiol levels and elevated jealousy responses during the time of rising and high fertility. These cyclical changes in female sexual behavior across the menstrual cycle suggest that females’ responses to a potential rival may also vary across the menstrual cycle and with estradiol levels. Therefore, it is possible that any evolved psychological or behavioral dispositions regarding reproduction-related relationships are potentially moderated by estradiol levels.