Abstract
Because cross-species evidence suggests that high testosterone (T) may interfere with paternal investment, the relationships between men's transition to parenting and changes in their T are of growing interest. Studies of human males suggest that fathers who provide childcare often have lower T than uninvolved fathers, but no studies to date have evaluated how nighttime sleep proximity between fathers and their offspring may affect T. Using data collected in 2005 and 2009 from a sample of men (n = 362; age 26.0 ± 0.3 years in 2009) residing in metropolitan Cebu, Philippines, we evaluated fathers' T based on whether they slept on the same surface as their children (same surface cosleepers), slept on a different surface but in the same room (roomsharers), or slept separately from their children (solitary sleepers). A large majority (92%) of fathers in this sample reported practicing same surface cosleeping. Compared to fathers who slept solitarily, same surface cosleeping fathers had significantly lower evening (PM) T and also showed a greater diurnal decline in T from waking to evening (both p<0.05). Among men who were not fathers at baseline (2005), fathers who were cosleepers at follow-up (2009) experienced a significantly greater longitudinal decline in PM T over the 4.5-year study period (p<0.01) compared to solitary sleeping fathers. Among these same men, baseline T did not predict fathers' sleeping arrangements at follow-up (p>0.2). These results are consistent with previous findings indicating that daytime father-child interaction contributes to lower T among fathers. Our findings specifically suggest that close sleep proximity between fathers and their offspring results in greater longitudinal decreases in T as men transition to fatherhood and lower PM T overall compared to solitary sleeping fathers.
Highlights
Humans are one of the few mammalian species in which fathers are heavily invested in their offspring and, often assist mothers in the direct care of young [1]
Like other mammals in which fathers care for offspring, human males must shift behavioral and energetic priorities after becoming parents in order to fulfill the requirements of paternal investment [2,3]
These findings suggest that elevated T likely facilitates somatic growth and behavioral priorities that enhance men’s mating effort but may reduce resources fathers have available for parental investment and diminish their sensitivity to offspring needs
Summary
Humans are one of the few mammalian species in which fathers are heavily invested in their offspring and, often assist mothers in the direct care of young [1]. Because T has been found to facilitate and enhance male mating effort through its influences on traits such as skeletal muscle and ornamentation as well as behaviors related to competition with other males and attraction of females [5,6,7,8,9], high T may conflict with effective fathering [10,11,12,13], potentially reducing offspring well-being and survival. Fathers with lower baseline T have been found to engage in more hands-on caregiving behaviors in observed parent-child interactions [30] These findings suggest that elevated T likely facilitates somatic growth and behavioral priorities that enhance men’s mating effort but may reduce resources fathers have available for parental investment and diminish their sensitivity to offspring needs
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