Importance of Grandparental Investment
Grandparental investment can be defined as all actions that may increase grandchildren’s fitness at any opportunity cost to grandparents’ own fitness. Grandparental investment includes conscious and unconscious investments grandparents channel toward their grandchildren. Grandparents can invest in their grandchildren either directly or indirectly via a third party (mostly via grandchildren’s parents). Grandparental investments include, for instance, contacts with grandchildren, care, financial help, emotional support, and practical help. Evolutionary importance of grandparental investment refers to fitness benefits that grandparents may gain by providing support to their offspring. By investing in their grandchildren, grandparents can increase their own inclusive fitness (i.e., spreading their genes in future generations) by two important ways. First, by investing in their offspring, grandparents can boost parental fertility. Second, grandparental investment may increase grandchild health, well-being, and survival.
Because of the demographic chances, grandparents today have a potential to be more important for child well-being than ever before. Increased life expectancy in modern Western countries means that grandparents and grandchildren have more shared years than before. Decreased fertility rates in turn denote that grandparents have fewer grandchildren, and thus they may be able to invest more in any particular grandchild. Regardless of this, grandparental effect in contemporary societies tends to be relatively small.
Grandparental Importance in Past and Present Societies
In premodern and historical populations, grandparental effect is measured by grandparental presence in same household or same village with their offspring rather than grandparental investment per se. In these populations grandparental presence is often found to correlate with both improved parental fertility and grandchild survival. However, all grandparents are not found to have similar effects. Studies have shown that paternal grandparents may improve fertility more than maternal grandparents (Sear and Coall 2011). In contrast, maternal grandmothers tend to increase grandchild survival more than maternal grandfathers or paternal grandparents (Sear and Mace 2008). These results can be explained by different sex-specific reproductive interests between women and men, which can be expanded to maternal and paternal grandparents (Euler 2011). Although, in several studies grandparental presence is found to benefit parents and grandchildren, kin relations include also conflicts. If grandparents push higher fertility and shorter birth intervals in females, this may have detrimental effects for both parents and grandchildren (Mace and Sear 2005). Moreover, in older age grandparents can be net consumers rather than net producers and could compete over local resources with grandchildren. This competition, in turn, may have detrimental effects for grandchildren (Strassmann 2011).
Grandparental investment can still be associated with parental fertility and grandchild well-being in modern Western societies. In the case of parental fertility, the existing evidence is, however, scarce and mixed. While some have found that grandparental investment is associated with increased fertility (e.g., Tanskanen et al. 2014), some others have not detected such an association (e.g., Aassve et al. 2012). Moreover, the form of grandparental investment is found to influence the results. For instance, a study from the UK found no association between grandparental child care help and parents’ childbearing, although emotional closeness between parental and grandparental generations was associated with improved fertility (Waynforth 2011). In contrast, a study from the Netherlands showed that grandparental support with child care was indeed associated with parental childbearing (Kaptijn et al. 2010).
In modern affluent countries, grandparents are not needed to keep their grandchildren alive as much as they were in subsistence societies. However, in present-day societies grandparental investment can still benefit grandchildren by improving grandchild well-being measured by, for instance, early years development, school success, and psychological well-being (Coall and Hertwig 2010). In particular, research has shown that in the cases of parental divorce, severe illness, and other family instabilities, grandparents can provide a buffer against these potentially harmful events (Sear and Coall 2011). As it was in premodern and historical populations, also in present-day societies, all grandparents tend to not benefit grandchildren similarly. In contemporary societies maternal grandparents are often found to improve grandchild well-being more than paternal grandparents (Sear and Coall 2011). Although in past populations the importance of grandfathers was small, in modern societies grandfathers may have as beneficial effect on grandchild well-being as grandmothers, at least in some circumstances (Sear and Coall 2011).
Evidence from both past and present societies shows that grandparents often boost parental fertility and child well-being. However, in some circumstances grandparents tend to have no effect at all, or they may have even detrimental effect. Thus, more research is needed to show in what circumstances grandparental investment may increase and in what circumstances decrease parental fertility and child well-being.
- Euler, H. A. (2011). Grandparents and extended kin. In C. A. Salmon & T. K. Shackelford (Eds.), The oxford handbook of evolutionary family psychology (pp. 181–207). New York: Oxford University Press.Google Scholar
- Mace, R., & Sear, R. (2005). Are humans cooperative breeders. In E. Voland, A. Chasiotis, & W. Schiefenhöve (Eds.), Grandmotherhood: The evolutionary significance of the second half of female life (pp. 143–159). New Brunswick: Rutgers University Press.Google Scholar