Abstract
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. 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. 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. 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.
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