Marital Status and Sleeping Arrangements Predict Salivary Testosterone Levels in Rural Gambian Men

Variation in male testosterone has been hypothesized to reflect the evolved hormonal regulation of investment in mating versus parenting effort. Supporting this hypothesis, numerous studies have observed lower testosterone in married men and fathers compared with unpartnered and childless men, consistent with relatively elevated resource allocation to parenting as opposed to mating effort. Furthermore, lower testosterone has been reported among fathers more actively engaged in direct caregiving. However, it remains unclear whether these findings generalize cross-culturally. Most studies have been conducted in relatively urban, affluent, and low fertility settings where marriage is predominantly monogamous. We contribute new data on testosterone variation in 100 rural Gambian men from a polygynous, high fertility population, where cultural norms dictate that marriage and fatherhood occur in close succession. Married men (almost exclusively fathers) had lower average morning salivary testosterone than unmarried men (almost exclusively childless). This difference, however, could not be statistically differentiated from declines in testosterone observed with age. Independently of age differences and other potential confounds, we find that (i) among married men, polygynously married men had higher afternoon testosterone than monogamously married men; and (ii) fathers who sleep in the same room as their children had lower morning and afternoon testosterone than those who sleep apart from their children. We also document that body mass index was positively associated with afternoon testosterone. These findings, from a novel setting, provide additional support for the hypothesis that testosterone regulates human paternal care.