Coall & Hertwig (C&H) present a wonderfully comprehensive and admirable review on the investing roles that grandparents play in traditional and modern societies. I would direct any of my students to this article if they were beginning research on the topic. Given that the article is so comprehensive, I restrict my comments to the history of this research in anthropology, especially as it relates to kin selection theory and some measurement issues that would better assess the ways in which grandparents matter.
There are several strands of research in evolutionary anthropology that deal with the role that grandmothers may play in enhancing the fertility of their children and survival of their grandchildren, beginning with the work of Turke (Reference Turke1989) and Kaplan (Reference Kaplan1994) on intergenerational resource transfers, the literature on “helpers at the nest” (for a review, see Hames & Draper Reference Hames and Draper2004), as well as reviews of the grandmother literature (Sear & Mace Reference Sear and Mace2008). To a limited extent, the theme of extended family intergenerational transfers is picked up by the authors in section 8.2 (under the heading of the “one-way street?”) and elsewhere. Turke and Kaplan criticized the work of the influential development demographer Caldwell (Reference Caldwell1976), who argued that high fertility in the developing world is a kind of social security mechanism whereby the elderly through high fertility produce children and eventually grandchildren who will support them in their old age. This strategy functions as insurance in social systems that lack effective social security. Turke and Kaplan note that Caldwell's model is a challenge to evolutionary demography and kin selection theory because the fitness concerns of family members, especially grandparents, should lead to a flow of wealth and resources from those who have low reproductive value to those who have greater reproductive value, adjusted by the coefficient of relatedness. If the flow were opposite, from younger to older, the fitness of the younger would be reduced, as well as the inclusive fitness of the older generation. The literature C&H review tends to support Turke and Kaplan's view in the modern context, but we need more research in the developing world, as exemplified by the research reviewed by Sear and Mace (Reference Sear and Mace2008).
The next research thread moved the focus from the extended family to a close examination of the impact of grandparents and was initiated by Hawkes and colleagues, beginning with their work on Hadza grandmothers (Hawkes et al. Reference Hawkes, O'Connell, Blurton Jones, Standen and Foley1989). These researchers argued that menopause was designed by natural selection to channel resources to grandoffspring. This insight generated a large amount of high quality research on grandmother effects on the survivorship of grandoffspring and the fertility of their children. C&H point out that much of this research is summarized in Hrdy's conceptualization of communal breeding (Hrdy Reference Hrdy, Hewlett and Lamb2005a) and in the general literature on helpers at the nest.
Viewing grandparental investment from a kin selection perspective would be methodologically useful for several reasons. First, grandparents have a wide variety of lineal and collateral kin as potential recipients of their benefits. It seems that research might be more profitably centered on how grandparents allocate their resources to all kin, including grandchildren, instead of focusing on how much grandchildren have received from grandparents. The grandparent to grandchild focus may hide transfers that grandparents may make to other kin. Although grandchildren are related by one-quarter to grandparents, the latter are related to their nephews and nieces to the same degree, even though the reproductive value of grandchildren is likely to be higher. Secondly, another problem that needs to be methodologically addressed is what can be called indirect transfers or the problem of targeting (Hames Reference Hames1987). Parents may be motivated to invest in their children because they know that such investments will be passed on to their grandchildren. For example, a monetary transfer to a child with a new-born grandchild may be motivated by a desire to invest in the grandchild by allowing its parents to make purchases that ultimately enhance the well-being of the grandchild. I would also add that the character of transfers should be sensitive to the age of the grandchild, such that initial investments may be in the form of direct grandparental care such as babysitting, to monetary transfers later in life for assistance in higher education.
Most of the studies in anthropology are demographic, in that they show correlations between grandmother presence and either enhanced survivorship of grandchildren or greater fertility of mothers. It is clear that we need more observational or more detailed survey research to learn exactly what grandparents do to cause these effects. This is particularly true of much of the ethnographic research in traditional societies, but much less true in wealthy countries, as C&H show. In ethnographic research, how grandchild survivorship and offspring fertility is achieved by the presence of grandparents is largely speculative, and C&H rightly note that such research only “highlight[s] potential behaviors that promote these beneficial effects” (sect. 2.5). Are mothers, for example, spared child-care activities to enhance their productivity, or do Hawkes et al.'s “hardworking Hadza grandmothers” (Hawkes et al. Reference Hawkes, O'Connell, Blurton Jones, Standen and Foley1989) produce food that is transferred to their daughters' households to enhance grandchild growth and development? These crucial sorts of investment could be measured in a variety of ways, such as carefully tracking data on actual transfers or through time allocation data (time diaries or direct observation). These measures are particularly important because they more accurately gauge the exact kinds of benefits from grandparents to offspring and their likely effects.
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Coall & Hertwig (C&H) present a wonderfully comprehensive and admirable review on the investing roles that grandparents play in traditional and modern societies. I would direct any of my students to this article if they were beginning research on the topic. Given that the article is so comprehensive, I restrict my comments to the history of this research in anthropology, especially as it relates to kin selection theory and some measurement issues that would better assess the ways in which grandparents matter.
There are several strands of research in evolutionary anthropology that deal with the role that grandmothers may play in enhancing the fertility of their children and survival of their grandchildren, beginning with the work of Turke (Reference Turke1989) and Kaplan (Reference Kaplan1994) on intergenerational resource transfers, the literature on “helpers at the nest” (for a review, see Hames & Draper Reference Hames and Draper2004), as well as reviews of the grandmother literature (Sear & Mace Reference Sear and Mace2008). To a limited extent, the theme of extended family intergenerational transfers is picked up by the authors in section 8.2 (under the heading of the “one-way street?”) and elsewhere. Turke and Kaplan criticized the work of the influential development demographer Caldwell (Reference Caldwell1976), who argued that high fertility in the developing world is a kind of social security mechanism whereby the elderly through high fertility produce children and eventually grandchildren who will support them in their old age. This strategy functions as insurance in social systems that lack effective social security. Turke and Kaplan note that Caldwell's model is a challenge to evolutionary demography and kin selection theory because the fitness concerns of family members, especially grandparents, should lead to a flow of wealth and resources from those who have low reproductive value to those who have greater reproductive value, adjusted by the coefficient of relatedness. If the flow were opposite, from younger to older, the fitness of the younger would be reduced, as well as the inclusive fitness of the older generation. The literature C&H review tends to support Turke and Kaplan's view in the modern context, but we need more research in the developing world, as exemplified by the research reviewed by Sear and Mace (Reference Sear and Mace2008).
The next research thread moved the focus from the extended family to a close examination of the impact of grandparents and was initiated by Hawkes and colleagues, beginning with their work on Hadza grandmothers (Hawkes et al. Reference Hawkes, O'Connell, Blurton Jones, Standen and Foley1989). These researchers argued that menopause was designed by natural selection to channel resources to grandoffspring. This insight generated a large amount of high quality research on grandmother effects on the survivorship of grandoffspring and the fertility of their children. C&H point out that much of this research is summarized in Hrdy's conceptualization of communal breeding (Hrdy Reference Hrdy, Hewlett and Lamb2005a) and in the general literature on helpers at the nest.
Viewing grandparental investment from a kin selection perspective would be methodologically useful for several reasons. First, grandparents have a wide variety of lineal and collateral kin as potential recipients of their benefits. It seems that research might be more profitably centered on how grandparents allocate their resources to all kin, including grandchildren, instead of focusing on how much grandchildren have received from grandparents. The grandparent to grandchild focus may hide transfers that grandparents may make to other kin. Although grandchildren are related by one-quarter to grandparents, the latter are related to their nephews and nieces to the same degree, even though the reproductive value of grandchildren is likely to be higher. Secondly, another problem that needs to be methodologically addressed is what can be called indirect transfers or the problem of targeting (Hames Reference Hames1987). Parents may be motivated to invest in their children because they know that such investments will be passed on to their grandchildren. For example, a monetary transfer to a child with a new-born grandchild may be motivated by a desire to invest in the grandchild by allowing its parents to make purchases that ultimately enhance the well-being of the grandchild. I would also add that the character of transfers should be sensitive to the age of the grandchild, such that initial investments may be in the form of direct grandparental care such as babysitting, to monetary transfers later in life for assistance in higher education.
Most of the studies in anthropology are demographic, in that they show correlations between grandmother presence and either enhanced survivorship of grandchildren or greater fertility of mothers. It is clear that we need more observational or more detailed survey research to learn exactly what grandparents do to cause these effects. This is particularly true of much of the ethnographic research in traditional societies, but much less true in wealthy countries, as C&H show. In ethnographic research, how grandchild survivorship and offspring fertility is achieved by the presence of grandparents is largely speculative, and C&H rightly note that such research only “highlight[s] potential behaviors that promote these beneficial effects” (sect. 2.5). Are mothers, for example, spared child-care activities to enhance their productivity, or do Hawkes et al.'s “hardworking Hadza grandmothers” (Hawkes et al. Reference Hawkes, O'Connell, Blurton Jones, Standen and Foley1989) produce food that is transferred to their daughters' households to enhance grandchild growth and development? These crucial sorts of investment could be measured in a variety of ways, such as carefully tracking data on actual transfers or through time allocation data (time diaries or direct observation). These measures are particularly important because they more accurately gauge the exact kinds of benefits from grandparents to offspring and their likely effects.