Coall & Hertwig (C&H) argue that in contemporary affluent societies grandparental investments are no longer likely to have a substantial positive effect on classical fitness indicators like child mortality. However, child mortality is only one component of fitness. Other components such as fertility and age at first reproduction have gained more importance in modern societies. In these societies, grandparental investments may relieve some of the important impediments on women's reproduction and in this way have a positive influence on fertility. Recent, yet unpublished, research supports this hypothesis.
Even though under modern conditions almost all children stay alive after birth, there are considerable impediments to women's reproduction. Partly these impediments have biological causes and are not limited to modern societies. Other impediments are more typical for contemporary societies. First, as C&H indicate (sect. 5.3.), the parental investments required to enable a child to compete with its peers have increased exponentially. These high costs of children limit the number of children the parents can raise. Second, paid employment and motherhood are hard to reconcile. When women are confronted with the dilemma of combining work and motherhood, they tend to reduce their fertility. This phenomenon is reflected in total fertility rates, which generally are lower in countries where work and motherhood are less compatible (Hoem Reference Hoem2008; McDonald Reference McDonald2000). Third, the acceptance and large-scale use of contraceptives have made fertility subject to conscious choice. In liberal societies, women's lifestyle preferences have a bigger impact on fertility decisions. Women's preferences are heterogeneous and some women prefer to be “childfree” (Hakim Reference Hakim2002; Reference Hakim2003).
The diverse impediments that women and couples face are likely to affect their reproductive success. It is our hypothesis that grandparental investments, especially investments in the form of childcare, alleviate these impediments and thus have a positive impetus on fertility. By reducing some of the burden of raising children, grandparental investments may lower the costs of a child for the parents. Grandparental childcare may also ease women's dilemma of combining paid employment and motherhood, and give the mother more possibilities to spend free time without the children. We tested this hypothesis in a representative sample of the contemporary Dutch older population for which information on grandparental babysitting, as well as the fertility of their children, was available. In this prospective study (yet unpublished), we found that grandparental childcare support has a positive effect on their children's fertility. This suggests that grandparental investments may also positively affect their children's fitness in a contemporary affluent society.
A positive relationship between grandparental investments and children's fertility on an individual level is not at odds with a negative relationship between grandparental investments and fertility on a population level as reported by C&H (sect. 8.3.), but rather points to the importance of the institutional context in which grandparental investments take place. It may well be that on a country level, grandparental childcare does not outweigh fertility constraining factors. Our findings are limited to a Dutch population and do not allow conclusions on the role of contextual factors. But, like C&H, we think this is an important new field of inquiry. Besides C&H's emphasis on the importance of economic and institutional factors, we want to stress that cultural factors may also be very important, both in shaping the preferences for care from grandparents, and in its impact on fertility.
The literature on European welfare state regimes (Esping-Andersen Reference Esping-Andersen1990; Pfau-Effinger Reference Pfau-Effinger2005) typically links the availability of care to cultural traditions about the role of women and kin in providing care. Roughly speaking, the farther south one gets, the greater the responsibility of women for their children, and the greater the reliance on kin for providing care. The northern countries provide more formal arrangements. The Netherlands stands out for its relatively high availability of child-care in combination with a strong preference of many working women for care from grandparents (Portegijs et al. Reference Portegijs, Cloin, Ooms and Eggink2006). This suggests first that the reliance on grandparents may be informed by cultural preferences, which are not only reflected in the institutional care arrangements, but also in the choices individual parents make.
Second, from an evolutionary perspective, the main question would be how child-care arrangements affect fertility. Does it make a difference if grandparents take care of the children, as compared to non-kin or even relative strangers? Or have our collective institutions simply taken over the role of grandparents in our evolution, as C&H suggest? The latter could be the case if we see our social institutions and society at large as an extension of the kin groups that presumably existed when the grandmother effect first emerged in humans. Recent findings indicate that fertility may be increasing in better-developed welfare states (Myrskylä et al. Reference Myrskylä, Kohler and Billari2009), and older generations often use the transfers they receive from the welfare state to invest in their children (Kohli Reference Kohli1999). This suggests that the mechanisms behind intergenerational transfers are similar at both macro and micro levels.
However, C&H show that most evolutionary perspectives on grandparental investments would predict a fitness advantage of taking care of grandchildren. When, as in the Dutch case, grandparents are willing to provide this care, and many parents prefer such care over other possibilities, it seems logical to expect that it also makes a greater difference for the parents' fertility. In that case, cultural preferences could reflect evolutionary advantages of grandparental care. The question then is if and why cultural differences occur in the relevance of grandparents for fertility. We have no answers yet, and at this moment we only have one study to suggest that grandparents do matter for fitness in low-risk countries. We hope this does make a case for further research on grandparental fitness effects, either by looking into the parents' situation in more detail, or by comparing data from countries with contrasting child-care and cultural backgrounds.
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Coall & Hertwig (C&H) argue that in contemporary affluent societies grandparental investments are no longer likely to have a substantial positive effect on classical fitness indicators like child mortality. However, child mortality is only one component of fitness. Other components such as fertility and age at first reproduction have gained more importance in modern societies. In these societies, grandparental investments may relieve some of the important impediments on women's reproduction and in this way have a positive influence on fertility. Recent, yet unpublished, research supports this hypothesis.
Even though under modern conditions almost all children stay alive after birth, there are considerable impediments to women's reproduction. Partly these impediments have biological causes and are not limited to modern societies. Other impediments are more typical for contemporary societies. First, as C&H indicate (sect. 5.3.), the parental investments required to enable a child to compete with its peers have increased exponentially. These high costs of children limit the number of children the parents can raise. Second, paid employment and motherhood are hard to reconcile. When women are confronted with the dilemma of combining work and motherhood, they tend to reduce their fertility. This phenomenon is reflected in total fertility rates, which generally are lower in countries where work and motherhood are less compatible (Hoem Reference Hoem2008; McDonald Reference McDonald2000). Third, the acceptance and large-scale use of contraceptives have made fertility subject to conscious choice. In liberal societies, women's lifestyle preferences have a bigger impact on fertility decisions. Women's preferences are heterogeneous and some women prefer to be “childfree” (Hakim Reference Hakim2002; Reference Hakim2003).
The diverse impediments that women and couples face are likely to affect their reproductive success. It is our hypothesis that grandparental investments, especially investments in the form of childcare, alleviate these impediments and thus have a positive impetus on fertility. By reducing some of the burden of raising children, grandparental investments may lower the costs of a child for the parents. Grandparental childcare may also ease women's dilemma of combining paid employment and motherhood, and give the mother more possibilities to spend free time without the children. We tested this hypothesis in a representative sample of the contemporary Dutch older population for which information on grandparental babysitting, as well as the fertility of their children, was available. In this prospective study (yet unpublished), we found that grandparental childcare support has a positive effect on their children's fertility. This suggests that grandparental investments may also positively affect their children's fitness in a contemporary affluent society.
A positive relationship between grandparental investments and children's fertility on an individual level is not at odds with a negative relationship between grandparental investments and fertility on a population level as reported by C&H (sect. 8.3.), but rather points to the importance of the institutional context in which grandparental investments take place. It may well be that on a country level, grandparental childcare does not outweigh fertility constraining factors. Our findings are limited to a Dutch population and do not allow conclusions on the role of contextual factors. But, like C&H, we think this is an important new field of inquiry. Besides C&H's emphasis on the importance of economic and institutional factors, we want to stress that cultural factors may also be very important, both in shaping the preferences for care from grandparents, and in its impact on fertility.
The literature on European welfare state regimes (Esping-Andersen Reference Esping-Andersen1990; Pfau-Effinger Reference Pfau-Effinger2005) typically links the availability of care to cultural traditions about the role of women and kin in providing care. Roughly speaking, the farther south one gets, the greater the responsibility of women for their children, and the greater the reliance on kin for providing care. The northern countries provide more formal arrangements. The Netherlands stands out for its relatively high availability of child-care in combination with a strong preference of many working women for care from grandparents (Portegijs et al. Reference Portegijs, Cloin, Ooms and Eggink2006). This suggests first that the reliance on grandparents may be informed by cultural preferences, which are not only reflected in the institutional care arrangements, but also in the choices individual parents make.
Second, from an evolutionary perspective, the main question would be how child-care arrangements affect fertility. Does it make a difference if grandparents take care of the children, as compared to non-kin or even relative strangers? Or have our collective institutions simply taken over the role of grandparents in our evolution, as C&H suggest? The latter could be the case if we see our social institutions and society at large as an extension of the kin groups that presumably existed when the grandmother effect first emerged in humans. Recent findings indicate that fertility may be increasing in better-developed welfare states (Myrskylä et al. Reference Myrskylä, Kohler and Billari2009), and older generations often use the transfers they receive from the welfare state to invest in their children (Kohli Reference Kohli1999). This suggests that the mechanisms behind intergenerational transfers are similar at both macro and micro levels.
However, C&H show that most evolutionary perspectives on grandparental investments would predict a fitness advantage of taking care of grandchildren. When, as in the Dutch case, grandparents are willing to provide this care, and many parents prefer such care over other possibilities, it seems logical to expect that it also makes a greater difference for the parents' fertility. In that case, cultural preferences could reflect evolutionary advantages of grandparental care. The question then is if and why cultural differences occur in the relevance of grandparents for fertility. We have no answers yet, and at this moment we only have one study to suggest that grandparents do matter for fitness in low-risk countries. We hope this does make a case for further research on grandparental fitness effects, either by looking into the parents' situation in more detail, or by comparing data from countries with contrasting child-care and cultural backgrounds.