General Theoretical Approach:
Much of the research in this lab combines evolutionary psychology with human behavioral endocrinology in order to discover the evolved functions of human endocrine signals. At a general theoretical level, what are hormones for? In a review article (Roney, 2016), I argued that the abstract function of hormones is coordination. Because they are released into the general circulation, hormones reach target cells distributed widely throughout the brain and body and can thereby simultaneously adjust diverse mechanism settings in ways that are functional responses to the eliciting conditions that triggered the hormone release. Given this, a logical way to study hormones is to build and test theories of how the natural eliciting conditions that trigger hormone responses are mapped into functional, coordinated output responses via the hormone changes. We call these mappings of eliciting conditions to hormone responses to coordinated output effects “theoretical frameworks” for specific hormones. A number of our empirical projects are contributing to the construction of such theoretical frameworks.
Hormone Response to Potential Mates:
One eliciting condition that reliably triggers reactive hormone increases in many nonhuman species is exposure to potential mates. For example, a range of nonhuman vertebrate males exhibit rapid, transient increases in testosterone and cortisol (or corticosterone) after non-tactile exposure to conspecific females and their stimuli. Other research shows that such transient increases have rapid effects on outcomes such as risk-aversion and aggressiveness that may promote immediate courtship effort. Our lab was the first to test for such hormone responses in humans. In a series of randomized experiments, this research has shown that brief social interactions with young women trigger rapid increases in both testosterone and cortisol in young men (see Publications for a list of articles). An NSF Social Psychology research grant awarded in 2014 is funding a series of ongoing experiments that expand the investigation of hormone responses to potential mates. This research is the first to test endocrine responses of women participants to interactions with potential mates; expands the number of hormones investigated to include oxytocin, estradiol, and progesterone; and investigates the effects of experimentally manipulated feelings of closeness as potential moderators of hormone responses.The first manuscripts reporting results from these experiments are nearing completion and will report the largest and most comprehensive investigations yet available on human endocrine responses to initial social interactions.
Ovarian Hormones and Women's Mating Effort:
Hormonal indices of fecundity (i.e. the probability of successful conception and gestation) have coordinated somatic and psychological/behavioral effects. Essentially, when energetic conditions are sufficient, dominant follicle maturation leads to cyclic patterns of estradiol and progesterone production that in turn have coordinated effects on the soma (e.g., preparation of the uterine lining for implantation) and the brain (e.g., changes in motivational priorities). A number of publications from our lab have provided support for this general position.
With respect to women’s sexual motivation, for example, our lab has provided the most extensive evidence yet available regarding the hormonal predictors of sexual desire within natural menstrual cycles. Prior studies on this topic had both small numbers of participants and infrequent hormone sampling (usually 2-3 times per week), and had generally produced inconclusive results. In a study funded by a Hellman Family Faculty fellowship, our lab collected daily saliva samples and self-reports of sexual desire across 1-2 cycles from a sample of 52 undergraduate women. Using multi-level regression modeling to analyze the thousands of available hormone values, we found evidence for positive effects of estradiol and negative effects of progesterone on women’s self-reported sexual desire (Roney & Simmons, 2013). Sexual desire was also significantly higher inside the fertile window (i.e. days when conception is possible) than on other cycle days, as expected given the hormone effects since estradiol peaks during the fertile window whereas progesterone peaks after ovulation during the non-fecund luteal phase.
The function of these hormone effects may be to couple sexual behavior to those circumstances when its ancestral fitness benefits were highest relative to its fitness costs. Decreased sexual motivation during non-fecund portions of the cycle may also function to allocate attention and motivation to adaptive problems other than mating when conception is not possible. Consistent with this, in many nonhuman mammals, ovarian hormones have effects on feeding and foraging that are exactly opposite to their effects on sexual motivation. Our lab has found evidence for this same pattern of opposite hormone effects in humans: women in the cycle phase study self-reported less food intake when their estradiol was higher, more when their progesterone was elevated, and also exhibited a pronounced drop in eating during the fertile window when conception was possible (Roney & Simmons, 2017). These findings support the idea that ovarian hormones are regulating tradeoffs in motivational priorities based on current fecundity: feeding motivation gets suppressed at precisely the time that sexual motivation peaks during the fertile window of the menstrual cycle.
Our lab is currently undertaking a large follow-up study that uses luteinizing hormone tests and salivary hormone samples to test hormonal and cycle phase predictors of women's body odors, motivational priorities, and reactions to social interactions. Other published research from our lab has provided evidence regarding hormonal predictors of women's mate preferences, body attractiveness, and clothing choices, as well as having demonstrated hormone responses to self-reported stress (see Publications for a list of articles).
Other Projects:
Although the above topics describe the main branches of the research program in the lab, members of the lab also have wider interests related to evolutionary psychology more generally. Rachel Grillot is developing an experimental approach to the study of human mate preferences for her dissertation that will soon introduce novel methods to the study of human mating. Adar Eisenbruch has developed a line of research that examines the determinants of human cooperative partner choice that is demonstrating the importance of cues to ancestral productivity, which complements the prior emphasis on cues of generosity and prosociality in the partner choice literature. Aaron Lukaszewski implemented novel empirical tests of whether facultative calibration processes may explain the origins of individual differences in human personality traits, among many other contributions that add a crucial functional dimension to the study of human personality. Zach Simmons contributed novel investigations of the roles of androgens in regulating men's energetic investment in mating vs. survival effort, including one of the first publications on the role of the androgen receptor gene in modulating components of men's intrasexual competitive effort. These are all outstanding scholars whose creativity and work ethic account for the research contributions of this lab.