Grandparental investment: the influence of reproductive timing and family size

David A Coall, University of Western Australia
Marc Meier, University of Basel
Ralph Hertwig, University of Basel
Michaela Wänke, University of Basel
François Höpflinger, University of Zürich

Some grandparents make substantial investments in their grandchildren while others make none. Several evolutionary concepts have been used to identify stable patterns of grandparental investment. We use data on six aspects of 580 Swiss grandparent-grandchild relationships to examine whether grandparents’ reproductive timing and their number of children and grandchildren influence the investment they make in their grandchildren. Generally, having more children or grandchildren reduced grandparental investment. After adjustment for a wide range of factors, having more children or grandchildren and having a first child or grandchild at a younger age were associated with reduced investment in 7 out of 12 analyses (all Ps < 0.09). Controlling for the grandparent’s family size accounted for more of the association between reproductive scheduling and investment than did adjusting for the grandchild’s family size. Conceptualizing grandparental investment as part of a grandparent’s reproductive strategy provides useful insights into the grandparent-grandchild relationship.