Sharing and caring: Testosterone, fathering, and generosity among BaYaka foragers of the Congo Basin

Hormone physiology and sleep dynamics among BaYaka foragers of the Congo Basin: Gendered associations between nighttime activity, testosterone, and cortisol

Sleep quality is an important contributor to health disparities and affects the physiological function of the immune and endocrine systems, shaping how resources are allocated to life history demands. Past work in industrial and post-industrial societies has shown that lower total sleep time (TST) or more disrupted nighttime sleep are linked to flatter diurnal slopes for cortisol and lower testosterone production. There has been little focus on these physiological links in other socio-ecological settings where routine sleep conditions and nighttime activity demands differ. We collected salivary hormone (testosterone, cortisol) and actigraphy-based sleep data from Congolese BaYaka foragers (N = 39), who have relatively short and fragmented nighttime sleep, on average, in part due to their typical social sleep conditions and nighttime activity. The hormone and sleep data collections were separated by an average of 11.23 days (testosterone) and 2.84 days (cortisol). We found gendered links between nighttime activity and adults' hormone profiles. Contrary to past findings in Euro-American contexts, BaYaka men who were more active at night, on average, had higher evening testosterone than those with lower nighttime activity, with a relatively flat slope relating nighttime activity and evening testosterone in women. Women had steeper diurnal cortisol curves with less disrupted sleep. Men had steeper cortisol diurnal curves if they were more active at night. BaYaka men often hunt and socialize when active at night, which may help explain these patterns. Overall, our findings indicate that the nature of nighttime activities, including their possible social and subsistence contexts, are potentially important modifiers of sleep quality-physiology links, meriting further research across contexts.

The prosociality of married people: Evidence from a large multinational sample

Single people are more likely to die from COVID-19. Here we study whether this higher death rate could be partly explained by differences in compliance with protective health measures against COVID-19 between single and married people, and the drivers of this marital compliance gap. Data collected from 46,450 respondents in 67 countries reveal that married people are more likely to comply with protective measures than single people. This marital gap in compliance is higher for men (approximately 5%) than for women (approximately 2%). These results are robust across a large range of countries and independent of country level differences with respect to culture, values or infection rates. Prosocial characteristics linked to morality and social belonging explain more than 38% of the marital gap, while individual risk perceptions play a minor role. These findings help explain single people's and particularly single men's greater vulnerability to COVID-19, which in turn can be leveraged to improve the effectiveness of international public policy campaigns aimed at promoting protective health measures.

Links between household and family social dynamics with sleep profiles among BaYaka foragers of the Congo Basin

Given the contributions of sleep to a range of health outcomes, there is substantial interest in ecological and environmental factors, including psychosocial contexts, that shape variation in sleep between individuals and populations. However, the links between social dynamics and sleep are not well-characterized beyond Euro-American settings, representing a gap in knowledge regarding the way that local socio-ecological conditions interrelate with sleep profiles across diverse settings. Here, we focused on data from a subsistence-level society in Republic of the Congo to test for links between the household/family social environment and sleep measures. Specifically, we used actigraphy-derived sleep data (N = 49; 318 nights) from two community locations (a village and rainforest camp) among BaYaka foragers, who are members of a remote, non-industrialized subsistence society in the Congo Basin. We drew on social dynamics that have been previously linked to sleep variation in Euro-American contexts, including: household crowding, same surface cosleeping, and marital conflict. We examined the following sleep measures: total sleep time (TST), total 24-h sleep time (TTST), and sleep quality (fragmentation). BaYaka adults had shorter and lower quality sleep when their shared sleeping space was more crowded. In the village, parents with breastfeeding-aged infants had longer TTST and higher quality sleep than adults without infants, contrasting with results from other cultural contexts. Based on peer rankings of marital conflict, husbands showed longer and higher quality sleep in less conflicted marriages. Women showed the opposite pattern. These counter-intuitive findings for women may reflect the limitations of the measurement for wives' marital experiences. In total, these results point to the importance of considering local socio-ecological conditions to sleep profiles and underscore the need for expanded study of sleep and health outcomes in settings where shared sleep in constrained space is routine practice.

Evidence for an adolescent sensitive period to family experiences influencing adult male testosterone production

Across vertebrates, testosterone is an important mediator of reproductive trade-offs, shaping how energy and time are devoted to parenting versus mating/competition. Based on early environments, organisms often calibrate adult hormone production to adjust reproductive strategies. For example, favorable early nutrition predicts higher adult male testosterone in humans, and animal models show that developmental social environments can affect adult testosterone. In humans, fathers’ testosterone often declines with caregiving, yet these patterns vary within and across populations. This may partially trace to early social environments, including caregiving styles and family relationships, which could have formative effects on testosterone production and parenting behaviors. Using data from a multidecade study in the Philippines (n = 966), we tested whether sons’ developmental experiences with their fathers predicted their adult testosterone profiles, including after they became fathers themselves. Sons had lower testosterone as parents if their own fathers lived with them and were involved in childcare during adolescence. We also found a contributing role for adolescent father–son relationships: sons had lower waking testosterone, before and after becoming fathers, if they credited their own fathers with their upbringing and resided with them as adolescents. These findings were not accounted for by the sons’ own parenting and partnering behaviors, which could influence their testosterone. These effects were limited to adolescence: sons’ infancy or childhood experiences did not predict their testosterone as fathers. Our findings link adolescent family experiences to adult testosterone, pointing to a potential pathway related to the intergenerational transmission of biological and behavioral components of reproductive strategies.

Children's fingernail cortisol among BaYaka foragers of the Congo Basin: associations with fathers' roles

Children and mothers' cortisol production in response to family psychosocial conditions, including parenting demands, family resource availability and parental conflict, has been extensively studied in the United States and Europe. Less is known about how such family dynamics relate to family members' cortisol in societies with a strong cultural emphasis on cooperative caregiving. We studied a cumulative indicator of cortisol production, measured from fingernails, among BaYaka forager children (77 samples, n = 48 individuals) and their parents (78 samples, n = 49) in the Congo Basin. Men ranked one another according to locally valued roles for fathers, including providing resources for the family, sharing resources in the community and engaging in less marital conflict. Children had higher cortisol if their parents were ranked as having greater parental conflict, and their fathers were seen as less effective providers and less generous sharers of resources in the community. Children with lower triceps skinfold thickness (an indicator of energetic condition) also had higher cortisol. Parental cortisol was not significantly correlated to men's fathering rankings, including parental conflict. Our results indicate that even in a society in which caregiving is highly cooperative, children's cortisol production was nonetheless correlated to parental conflict as well as variation in locally defined fathering quality. This article is part of the theme issue 'Multidisciplinary perspectives on social support and maternal-child health'.

Not all "caregivers" are created equal: Liking, caring and facial expression responses to the baby schema as a function of parenthood and testosterone

The baby schema elicits care from potential caregivers. However, much of the research on the baby schema is based on self-report only. To address this issue, we explored the effects of baby schema and child age on facial expressions (EMG) and eye-blink startle, in addition to self-reported liking and caring for 43 men and 48 women (39 parents). Further, basal testosterone was assessed. All groups responded with liking and caring to high baby schema, but only women also responded with more positive facial expressions. Caring and smiling towards infants compared to first graders depended on parenthood and testosterone levels. Basal testosterone levels were negatively associated with overall responsiveness to children in women and fathers, but positively in non-fathers. Whereas the baby schema overall lead to positive affect and caring, the scope of these responses and the processes underlying them depended on gender, parenthood and hormonal status.

Fathers' oxytocin responses to first holding their newborns: Interactions with testosterone reactivity to predict later parenting behavior and father-infant bonds

Little is known about human fathers' physiology near infants' births. This may represent a period during which paternal psychobiological axes are sensitive to fathers' new experiences of interacting with their newborns and that can provide insights on how individual differences in fathers' biology relate to post-partum parenting. Drawing on a sample of men in South Bend, IN (U.S.), we report results from a longitudinal study of fathers' oxytocin, cortisol, and testosterone (N = 211) responses to their first holding of their infants on the day of birth and men's reported caregiving and father-infant bonding at 2-4 months post-partum (N = 114). First-time fathers' oxytocin was higher following first holding of their newborns, compared to their pre-holding levels. Contrasting with prior results, fathers' percentage change in oxytocin did not differ based on skin-to-skin or standard holding. Drawing on psychobiological frameworks, we modeled the interactions for oxytocin reactivity with testosterone and cortisol reactivity, respectively, in predicting father-infant outcomes months later. We found significant cross-over interactions for (oxytocin × testosterone) in predicting fathers' later post-partum involvement and bonding. Specifically, we found that fathers whose testosterone declined during holding reported greater post-partum play if their oxytocin increased, compared to fathers who experienced increases in both hormones. We also observed a similar non-significant interaction for (oxytocin × cortisol) in predicting fathers' post-partum play. Fathers whose testosterone declined during holding also reported less involvement in direct caregiving and lower father-infant bonding if their oxytocin decreased but greater direct care and bonding if their testosterone increased and oxytocin decreased. The results inform our understanding of the developmental time course of men's physiological responsiveness to father-infant interaction and its relevance to later fathering behavior and family relationships.