Do Step- and Biological Grandparents Show Differences in Investment and Emotional Closeness With Their Grandchildren?

Human children are raised by a variety of caregivers including grandparents. A few studies have assessed potential differences in direct caregiving, financial expenditures, and emotional closeness between biological and step-grandparents. Drawing upon kin selection theory, we hypothesized that step-grandparents would provide less care and be less emotionally close to grandchildren than would biological grandparents. A sample of 341 heterosexual U.S. adults 25–35 years of age in a long-term partnership and with a biological child 5 years of age or younger were recruited via Amazon Mechanical Turk. Subjects provided sociodemographic information and answered questions about the dynamics between their own parent/stepparent and their own youngest biological child (hence, biological/step-grandparenting dynamics). Main analyses were restricted to within-subject comparisons. Results showed that biological grandmothers provided more direct childcare, financial expenditures, and had more emotionally close relationships with grandchildren than did step-grandmothers. Biological grandfathers provided less direct care and had less emotionally close relationships than step-grandfathers but did not exhibit differences in financial expenditures. Biological grandmothers provided more direct care, financial investment, and were more emotionally close to the referential grandchild than were biological grandfathers. Step-grandfathers were more emotionally close and more often played with grandchildren than step-grandmothers. These findings partially support kin selection theory. We discuss the relevance of factors such as competing demands on grandmothers’ investment in biological and step-grandchildren and grandfathering serving in part as mating effort. Sex differences in biological grandparenting also mirror those in parenting. We suggest directions for future research, including on grandfathers, particularly in patrilineal societies.