Evolutionary versus socio-economic perspectives

The evolutionary biology view and the socio-economic view differ significantly in one point. Evolutionary biology does not assume that grandparents decide rationally when caring for grandchildren. Most behaviors are irrational, although humans have the ability to consider things from a rational point of view.

Human biology searches for universal behaviors and their variety. These behaviors have emerged over the course of evolution because they had an advantage for survival and reproduction. Human behaviors are influenced by emotions and shaped by the social and cultural environment in which we grow up. We learn from an early age what is expected from grandparents and their duties. This means that evolution affects human behavior in terms of both inner motivations and cultural learning. This is because evolution also shapes cultural systems. Grandparental roles must be learned, such as mothering behavior, by observation and experiences. This is not true only for humans, but also for other mammals, not the least being other primates (e.g., Lancaster et al. Reference Lancaster1971; Suomi Reference Suomi2003).

Sociology, by contrast, focuses on differences caused by social factors and the economic framework: How is grandparental caregiving characterized within a society, given the socio-economic conditions? And what has changed over time? Biology and sociology, in fact, do not overlap; however, they can complement each other. C&H combine the different interdisciplinary approaches, although they could make different perspectives clearer. When sociologists and economists analyze bidirectional intergenerational transfers within a modern Western society or the effects of government transfers, they have their focus on certain conditions. Evolutionary biologists, however, research the universal nature of human behavior, despite the different social-economical parameters.

Asymmetric grandparental care-giving is one such universal pattern that has been found in both sociology and evolutionary science independently of each other. Here, analyses of the underlying proximate mechanisms can be very helpful for an interpretation on an ultimate level. A strong correlation between the parent–grandparent relationship and the grandparents' care of grandchildren has been found (Michalski & Shackelford Reference Michalski and Shackelford2005; Pashos Reference Pashos2000; Steinbach & Henke Reference Steinbach and Henke1998; see also Korchmaros & Kenny Reference Korchmaros and Kenny2001), which can also explain the variance in asymmetric care-giving to a large degree (Pashos & McBurney Reference Pashos and McBurney2008). Understanding family relationships is hence not only a sociological topic, but also a key point for an evolutionary interpretation.

The Trivers–Willard hypothesis, or sex-biased grandparental investment, as it is called in the target article, should not be underestimated when explaining male-biased grandparental investment, as found in some traditional patrilineal rural societies (King et al. Reference King, Silverstein, Elder, Bengtson and Conger2003; Pashos Reference Pashos2000). In patrilateral systems, the investment in sons and grandsons appears to be superimposed upon the universal matrilineality of kin investment.

Significance of grandparents

Grandparental investment developed in evolutionary history because this help was necessary for the offspring's survival. In modern societies, there is an institutional infrastructure that supports parents with their childcare. Is the role of the helping family therefore dispensable nowadays? C&H correctly conclude that the positive effect of grandparental investment in Western societies should especially be seen with regard to “softer dimensions,” such as cognitive and verbal skills during child development and emotional support.

Grandparental investment involves solicitude, listening to problems, telling stories, having daily phone contact, giving protection and support, buying ice cream and toys, getting on one's knees to play with a toddler. These are universal grandparental roles, regardless of the economic conditions in a society. Thus, grandparents are not only “safeguards,” “when kids try to set fire to the carpet.” The problem is that these so-called softer dimensions, which can benefit child development, are difficult to measure.

Interpretations regarding the transfer of resources form grandparents to children and grandchildren using large socio-economical survey datasets must be done with care. Surveys such as SHARE or the German Aging Survey were not designed for evolutionary approaches. The “regular care” in the SHARE study is defined as “looking after any grandchildren without the presence of the parents.” That means that grandchild care can be equated with babysitting here, not with grandparental investment in general. Also, it was not recorded if the grandparents cared for all or only some of their grandchildren. An association of grandparental investment and fertility rates therefore cannot be interpreted with confidence, and is rather questionable.

Significance of grandparenthood for elderly people

Another important problem is the effects of grandparenthood on the elderly people. The authors draw a nonlinear relationship between grandchild care and grandparents' well-being. From an evolutionary theory point of view, the purpose of the mathematical function is not fully clear to me. Investment is always costly. The advantage of kin investment lies in the inclusive-fitness benefit. When your child falls into freezing water, and you jump after him, this is, of course, harmful to you. Grandchild care can be exhausting, especially in the “high-risk” context. Surely, it is no full substitute for parental care and the elderly's power is limited. Nevertheless, grandparents are often willing to sacrifice themselves for their grandchildren, more than other kin and non-kin.

But what are their motives? Well-being, life satisfaction, and happiness could be more clearly distinguished. In a data analysis using the German Aging Survey, I found that the existence of grandchildren, and even of children, does not make elderly people more satisfied with their lives (Pashos Reference Pashos2009). However, grandchildren were very often listed as persons who give great pleasure and happiness. Elderly people without grandchildren were much less able to name persons who gave pleasure and happiness to them, especially with increasing age (Fig. 1). Grandparents also were on average somewhat less lonely than their grandchildless counterparts.

Figure 1.

“Are there persons who currently give you great pleasure or great happiness? (Yes=1)” by “Age class” and “Presence of biological grandchildren.”

Source: German Aging Study (Tesch-Römer et al. Reference Tesch-Römer, Wurm, Hoff and Engstler2002). Available at: http://www.dza.de/nn_12036/SharedDocs/Publikationen/Alterssurvey_Instrumente,templateId=raw,property=publicationFile.pdf/Alterssurvey_Instrumente.pdf

These additional results suggest that the motivation for grandparents to care must not necessarily be looked for in physical and psychological well-being or even the satisfaction with life. Grandparenthood, however, does seem to have an emotional impact on elderly people. It might give them a happy feeling that they are still needed.