Grandfather Investment Versus Grandmother Investment
The investment of grandfathers and grandmothers includes different types of support and resources grandparents can target toward their grandchildren. Grandparental investments can include different types of actions, for instance, financial transfers, emotional support, and care. Grandparents can invest in their grandchildren either directly or indirectly via a third party (e.g., via the grandchildren’s parents). Typically, grandfathers tend to invest less in their grandchildren than grandmothers, except when comparing paternal grandmother’s and maternal grandfather’s investment.
Grandparents share, on average, 25% of the same genes with their grandchildren, and thus, they can increase their inclusive fitness by investing time and resources in their descendants. Nonetheless, all grandparent types tend not to be in the same position with each other in their relations with grandchildren (Tanskanen and Danielsbacka 2018). Only maternal grandmothers can be 100% certain of their relatedness to grandchildren, while maternal grandfathers (via themselves and their daughters) and paternal grandmothers (via their sons and their children) have one link of uncertain paternity, and paternal grandfathers have two (via themselves and sons and via sons and sons’ children). Hence, within the kin lineages, grandmothers are more likely to be genetically related to their descendants compared to grandfathers, meaning that maternal grandmothers are expected to invest more than maternal grandfathers and paternal grandmothers more than paternal grandfathers. This entry considers the role of grandfather investment compared to grandmother investment.
Grandfather and Grandmother Investment
Although the role of grandfathers could have been relatively minor in traditional and historical populations (Sear and Mace 2008), in contemporary nations, grandfathers are often highly involved in their grandchildren’s lives. Indeed, in some circumstances, the investment of grandfathers can approach that of grandmothers. For instance, based on cross-national evidence from Europe, 58% of grandmothers and 49% of grandfathers look after their grandchildren at least occasionally (Hank and Buber 2009). Moreover, in current societies, the investment of both grandmothers and grandfathers is observed to be associated with improved child well-being (Sear and Coall 2011), although it is unclear whether there is a causal association between grandparental investment and child outcomes (Tanskanen and Danielsbacka 2017).
In addition to sex-based differences (i.e., sex effect), grandparental investment varies by lineage, meaning that maternal grandmothers usually invest the most, followed by maternal grandfathers, then paternal grandmothers, and, finally, paternal grandfathers (Coall and Hertwig 2010; Euler 2011). Among evolutionary scientists, the most important explanation for this biased grandparental investment pattern is based on paternity uncertainty. However, paternity uncertainty cannot directly explain why maternal grandfathers often invest more than paternal grandmothers.
With regard to preferential investment in more certain kin theory, the amount of grandparental investment changes according to the availability of other “investment options” (Laham et al. 2005). If grandmothers and grandfathers have grandchildren via both daughters and sons, they are expected to invest more in their daughter’s children compared to their son’s children. If grandchildren via daughters do not exist, grandparents are expected to invest more in grandchildren via sons. Often, maternal grandfathers may invest more than paternal grandmothers because the latter typically have more certain investment options (i.e., grandchildren via daughters). If more certain investment options are unavailable, maternal grandfather and paternal grandmother should invest equally in their grandchildren. A previous study including over 22,000 European grandparents provided evidence in support of the preferential investment theory (Danielsbacka et al. 2011).
In recent decades, there has been increasing academic interest in the grandparental role in human families. However, an obvious limitation in many of these studies is that older men have often been ignored and, in practice, “grandparents” have been used as a synonym for “grandmothers” (Coall et al. 2016). Although grandmothers are known to invest more time and resources in grandchildren than grandfathers, the role of grandfathers is far from negligible. Thus, when one considers grandparental investment, it is important to consider also the role of grandfathers.
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- Tanskanen, A. O., & Danielsbacka, M. (2017). Multigenerational effects on children’s cognitive and socioemotional outcomes: A within-child investigation. Child Development, 88. https://doi.org/10.1111/cdev.12968.
- Tanskanen, A. O., & Danielsbacka, M. (2018). Intergenerational family relations. An evolutionary social science approach. London: Routledge.Google Scholar