Investigating potential hormonal associations of grandmaternal care in Jamaica

There has been increasing scholarly interest in the role of grandmothers in human evolution and cross-culturally. An unaddressed question is the proximate mechanisms associated with human grandmaternal care. Here, we report on results of a naturalistic study conducted in greater Kingston, Jamaica designed to test for betweenand within-subject effects of grandmaternal care on women’s cortisol, oxytocin, vasopressin, and prolactin levels. We recruited 25 women who lived with and provided care for a biological grandchild aged five or younger (grandmothers) in addition to 20 women of similar ages, socioeconomic status, and health status who did not similarly provide such care (controls). Women were aged 50-67 and postmenopausal. Interviews and biological sample collection took place either in women’s homes or a nearby church. While control women participated on a single day, grandmothers participated on two days: one day when they had been caring for their youngest grandchild the previous four hours, and another day when not providing such care the previous four hours. Hormonal data revealed that grandmothers had significantly higher vasopressin levels than control women, but did not exhibit differences in cortisol, oxytocin, and prolactin compared with control women. Results also revealed no significant differences in hormone levels on days grandmothers provided vs. did not provide care the previous four hours. Findings from this first study investigating hormones associated with grandmaternal care can be situated in light of the comparative physiology of affiliative behavior and methodological considerations.