Peter T. Ellison’s research while affiliated with Harvard University and other places

The largest reported sex difference in human cognition is found on mental rotation tests, which ask participants to compare pictures of three-dimensional objects and decide whether they depict the same or different objects. When the objects are the same, one can be rotated two- or three-dimensionally to match the other. Across cultures, males score up to one standard deviation higher than females on these tests. We administered two mental rotation tests to 123 participants and found that these higher scores likely do not reflect superiority in the process of mental rotation per se, but rather in other aspects of task performance. We found: (1) men are more likely than women to answer correctly when two objects are different, whereas women are more likely to answer incorrectly that they are the same; and (2) individual differences in confidence explain a considerable portion of the male advantage, but differences in spatial encoding ability do not. These results suggest more attention should be paid to individual differences in the various components of spatial ability and task performance, and have implications for evolutionary theories of sex differences in spatial cognition and for efforts to reduce sex differences in spatial ability, especially via training interventions.

This chapter is a revised version of the Puberty chapter published in the second edition. The principal changes include updates to the proximate regulators of pubertal hypothalamic GnRH secretion, a brief section on epigenetics, and slight alterations in language to acknowledge that, while biological studies of puberty treat individuals as sexually dimorphic, lived experience varies. New references have been inserted among the pre-existing ones but have not been numbered so that, if revisions are required, the work of formatting and ordering need not take place a second time. They are highlighted in the bibliography to make them easily visible. All tables and figures remain the same except Fig. 5.3. If possible, I would like to include a revised version of this figure that appeared in an Annual Review of Anthropology article (by Reiches). That file is attached below.

The nervous system and the endocrine system interact to integrate behavior and physiolo­gy. Hormones play an important role in this interaction, particularly steroid hormones. Other molecules, notably oxytocin, can serve both as hormones in the soma and neuro­modulators in the central nervous system. Understanding the influence of the endocrine system on human behavior, both individual and social, has been a primary focus of behav­ioral endocrinology for many decades, though technical and methodological challenges have been formidable. The recent enthusiasm for enzyme-linked immunoassay kits for measuring steroid hormones in saliva has been found to be largely unsound, for example. Despite these difficulties, advances in many areas have been made and new areas, such as the endocrinology of paternal behavior and the role of oxytocin in social interactions, have emerged. Reproductive ecology provides a theoretical framework for integrating the di­verse content of human behavioral ecology.

Objectives Establish the variability of C‐reactive protein (CRP) within a population of first‐generation immigrants living in the United States. Prior work has theorized that individuals with high levels of childhood pathogen exposure may have lower CRP levels in adulthood, and therefore that for these individuals, CRP may not be as accurate an index of chronic disease risk related to low‐level inflammation as is presumed based on data from wealthy populations. This potentially has major implications for the interpretation of CRP as a biomarker of chronic inflammation. Methods This longitudinal study collected a total of 125 dried blood spot (DBS) samples from 31 participants (median 4 samples each) and CRP levels in these DBS were assayed by enzyme‐linked immunosorbant assay. Surveys were administered to characterize childhood pathogen exposure, and current illness. Variance was estimated using mixed effects regression models. Results On average, participants were adults (mean = 41.9 years old) who had immigrated to the United States nearly 20 years prior to the study and had nearly universally experienced childhood helminth infection and other major pathogen exposures. Median serum‐equivalent CRP was 0.77 mg/L. Individuals reliably differed in subacute CRP levels, and, depending on whether untransformed or log‐transformed CRP was the outcome variable, 45% or 62% of variance in CRP was attributable to between‐individual differences. Conclusions The variability of CRP levels in individuals with relatively high childhood pathogen exposure is comparable to previously reported studies in North America and Europe. However, CRP values are relatively low. CRP is an appropriate measure of subacute inflammation in this sample.

Objectives Relative to industrialized populations, men from subsistence groups exhibit lower testosterone values and more modest declines with age. Limited energy availability has been hypothesized to suppress testosterone production, particularly during young adulthood when testosterone levels are highest, resulting in a flatter trajectory of age-decline. Energetic constraint, however, is not unique to the evolutionary ecology of humans, and yet significant age-related testosterone decline is observed in numerous species of wild primates. Conversely, human life history is distinguished by extensive bi-parental care and male provisioning. Because fathers show decreased testosterone with parenting effort, we argue that within more naturalistic and evolutionarily relevant ecologies, natural fertility and earlier reproduction suppresses testosterone in emerging adulthood such that a lower relative baseline dictates less age-decline across the remaining lifespan. Methods We examine men’s testosterone levels as contrasting functions of energetic status and paternal involvement across three traditional populations with substantial variability in men’s nutritional condition and parental investment. Anthropometric and demographic data along with saliva samples were collected from 70 Datoga, 29 Hadza, and 43 Qom men, ages 20–72 years. Results Population variation in salivary testosterone was greatest at younger ages and patterned so paternal involvement associated with lower morning and evening testosterone, along with diminished age-decline in both measures. Men’s energetic status as indicated by body mass index was not associated with testosterone values or age-related decline. Conclusions Within socioecological contexts of smaller scale society, these data suggest that blunted age-decline in men’s testosterone levels is primarily due to population variation in parental investment rather than energetic constraint.

Human reproductive ecology developed as a field beginning in the 1980s from an intersection of demography, physiology, and evolutionary biology. Studies of numerous populations around the world living under diverse conditions have shown that female fecundity varies with energetic conditions, that male testosterone varies less sensitively, and that there are age patterns to gonadal function in both sexes, among other basic findings. Most of these patterns have analogs among nonhuman primates as well. More recent work is illuminating developmental influences on reproductive function, and exploring additional areas such as interactions with immune function.

Significance The energetic impact of immune function on human growth remains unclear. Using data from Amazonian forager-horticulturalists, we show that diverse, low-level immune activity predicts reduced childhood growth over periods of competing energy use ranging from 1 wk to 20 mo. We also demonstrate that modest body fat stores (i.e., energy reserves) protect children from the particularly detrimental impact of acute inflammation on growth. These findings provide evidence for considerable energetic tradeoffs between immune function and growth among humans, highlighting the energy constraint of childhood and the characteristic ability of our species to respond sensitively to dynamic environmental conditions. We outline the possible role of immune-related tradeoffs in driving patterns of human growth faltering, developmental metabolic plasticity, and life history evolution.