We conducted a meta-analysis of 17 studies that tested for an association between grandparental survival and grandchild survival in patrilineal populations. Using two different methodologies, we found that the survival of the maternal grandmother and grandfather, but not the paternal grandmother and grandfather, was associated with decreased grandoffspring mortality. These results are consistent with the findings of psychological studies in developed countries (Coall and Hertwig Behavioral and Brain Sciences 33:1-59, 2010). When tested against the predictions of five hypotheses (confidence of (...) paternity; grandmothering, kin proximity, grandparental senescence, and local resource competition), our meta-analysis results are most in line with the local resource competition hypothesis. In patrilineal and predominantly patrilocal societies, the grandparents who are most likely to live with the grandchildren have a less beneficial association than those who do not. We consider the extent to which these results may be influenced by the methodological limitations of the source studies, including the use of retrospective designs and inadequate controls for confounding variables such as wealth. (shrink)

Matriliny has long been debated by anthropologists positing either its primitive or its puzzling nature. More recently, evolutionary anthropologists have attempted to recast matriliny as an adaptive solution to modern social and ecological environments, tying together much of what was known to be associated with matriliny. This paper briefly reviews the major anthropological currents in studies of matriliny and discusses the contribution of evolutionary anthropology to this body of literature. It discusses the utility of an evolutionary framework in the context (...) of the first independent test of Holden et al.’s 2003 model of matriliny as daughter-biased investment. It finds that historical daughter-biased transmission of land among the Mosuo is consistent with the model, whereas current income transmission is not. In both cases, resources had equivalent impacts on male and female reproduction, a result which predicts daughter-biased resource transmission given any nonzero level of paternity uncertainty. However, whereas land was transmitted traditionally to daughters, income today is invested in both sexes. Possible reasons for this discrepancy are discussed. (shrink)

What motivates grandparents to their altruism? We review answers from evolutionary theory, sociology, and economics. Sometimes in direct conflict with each other, these accounts of grandparental investment exist side-by-side, with little or no theoretical integration. They all account for some of the data, and none account for all of it. We call for a more comprehensive theoretical framework of grandparental investment that addresses its proximate and ultimate causes, and its variability due to lineage, values, norms, institutions (e.g., inheritance laws), and (...) social welfare regimes. This framework needs to take into account that the demographic shift to low fecundity and mortality in economically developed countries has profoundly altered basic parameters of grandparental investment. We then turn to the possible impact of grandparental acts of altruism, and examine whether benefits of grandparental care in industrialized societies may manifest in terms of less tangible dimensions, such as the grandchildren's cognitive and verbal ability, mental health, and well-being. Although grandparents in industrialized societies continue to invest substantial amounts of time and money in their grandchildren, we find a paucity of studies investigating the influence that this investment has on grandchildren in low-risk family contexts. Under circumstances of duress there is converging evidence that grandparents can provide support that helps to safeguard their children and grandchildren against adverse risks. We conclude by discussing the role that grandparents could play in what has been referred to as Europe's demographic suicide. (shrink)

Low birth rates in developed societies reflect women’s difficulties in combining work and motherhood. While demographic research has focused on the role of formal childcare in easing this dilemma, evolutionary theory points to the importance of kin. The cooperative breeding hypothesis states that the wider kin group has facilitated women’s reproduction during our evolutionary history. This mechanism has been demonstrated in pre-industrial societies, but there is no direct evidence of beneficial effects of kin’s support on parents’ reproduction in modern societies. (...) Using three-generation longitudinal data anchored in a sample of grandparents aged 55 and over in 1992 in the Netherlands, we show that childcare support from grandparents increases the probability that parents have additional children in the next 8 to 10 years. Grandparental childcare provided to a nephew or niece of childless children did not significantly increase the probability that those children started a family. These results suggest that childcare support by grandparents can enhance their children’s reproductive success in modern societies and is an important factor in people’s fertility decisions, along with the availability of formal childcare. (shrink)

Based on historical data pertaining to the Krummhörn population (eighteenth and nineteenth centuries, Germany), we compared reproductive histories of mothers according to whether the maternal grandmother (MGM) or the paternal grandmother (PGM) or neither of them was resident in the parents’ parish at the time of the mother’s first birth. In contrast to effects of PGMs, we discovered conditional differences in the MGM’s effects between landless people and wealthier, commercial farmers. Our data indicate that the presence of the MGM only (...) lowers the woman’s age at marriage (AAM) and her age at the birth of her first child (AFB) in the case of landless families. However, among commercial farmers, who can generally be characterized by a lower AAM and AFB, we found opposite tendencies for the MGM’s effect leading to a relatively small delay in AAM and AFB. Moreover, we also analyzed differences in the completed fertility (i.e., children ever born: CEB). Results indicate that landless families in general do have fewer CEB compared with commercial farmers except for those families in which the MGM has been present. Emphasizing that the adaptiveness of investment decisions should depend on the interaction of genetic, lineage-specific (intrinsic) and ecologically imposed (extrinsic) constraints, we conclude that kin strategies consequently address different fitness components under different conditions. (shrink)

The mother–adult daughter relationship has been highlighted in both the social sciences and the public health literature as an important facet of social support networks, particularly as they pertain to maternal and child health. Evolutionary anthropologists also have shown positive associations between support from maternal grandmothers and various outcomes related to reproductive success; however, many of these studies rely on proximity as a surrogate measure of support. Here I present data from the Puerto Rican Maternal and Infant Health Survey (PRMIHS) (...) comparing geographic proximity of mother and daughter with a self-reported measure of mother-to-daughter support. These two measures were used to predict infant health outcomes as well as various measures of instrumental and emotional aid provided during pregnancy and after birth. Primary support was shown to have a positive effect across the analyses, whereas geographic proximity was associated with an increased risk of infant mortality and low birth weight as well as reduced odds of receiving support. This paradox was then examined using a combination variable that teased out the interactions of maternal support and proximity. Women who were geographically close to their mothers but who did not consider them a primary source of support had increased odds of infant death and low birth weight, and were less likely to receive either tangible or intangible forms of aid, while women whose mothers were both close and primary showed uniformly positive outcomes. These results place the role of propinquity within the larger context of social support and highlight the need for more detailed studies of social support within evolutionary anthropology. (shrink)

Coall & Hertwig (C&H) demonstrate the importance of grandparents to children, even in low fertility societies. We suggest policy-makers interested in reproductive timing in such contexts should be alerted to the practical applications of this cooperative breeding framework. The presence or absence of a supportive kin network could help explain why some women begin their reproductive careers or.

Under poor circumstances, co-residence of a grandmother is generally considered to be beneficial for children. Empirical evidence does not unequivocally support this expectation and suggests that the grandmother’s importance depends on the family’s circumstances. We study the relationship between grandmother’s co-residence and children’s schooling in sub-Saharan Africa under a broad range of circumstances. Results make clear that the effect of a co-residing grandmother varies but is almost always positive. Grandmothers over age 60 are most effective in helping their children. They (...) are particularly important for girls, and when the mother is deceased or not living in the household. Grandmothers are less effective in situations with few opportunities, as in very poor regions or in communities with few schooling opportunities. Our findings indicate that providing support to grandmothers should not be overlooked when designing policies aimed at strengthening the position of women and children in the sub-Saharan African context. (shrink)

This response outlines more reasons why we need the integrative framework of grandparental investments and intergenerational transfers that we advocated in the target article. We discusses obstacles that stand in the way of such a framework and of a better understanding of the effects of grandparenting in the developed world. We highlight new research directions that have emerged from the commentaries, and we end by discussing some of the things in our target article about which we may have been wrong.

The target article emphasizes the need to identify psychological mechanisms underlying grandparental investment, particularly in low-risk family contexts. We extend this approach by addressing the changing demands of balancing work and family in low-risk families. Taking a lifespan psychological perspective, we identify additional motivators and potential benefits of grandparental investment for grandparents themselves and for subsequent generations.

In discussing the effects of grandparents on child survival in natural fertility populations, Coall & Hertwig (C&H) rely extensively on the review by Sear and Mace (2008). We conducted a more detailed summary of the same literature and found that the evidence in favor of beneficial associations between grandparenting and child survival is generally weak or absent. The present state of the data on human alloparenting supports a more restricted use of the term Human stem family situations with celibate helpers-at-the-nest (...) can be described as cooperatively breeding, but the term is a poor fit to many human family systems. (shrink)

Weight- (WAZ), height- (HAZ), and BMI-for-age (BMIZ) are frequently used to assess malnutrition among children. These measures represent different categories of risk and are usually hypothesized to be affected by distinct factors, despite their inherent relatedness. Life history theory suggests weight should be sacrificed before height, indicating a demonstrable relationship among them. Here we evaluate impact of family composition and household economics on these measures of nutritional status and explore the role of WAZ as a factor in HAZ. Anthropometrics, family (...) demographics, and measures of household economy were collected from Sidama agropastoralist children in a peri-urban village in southwestern Ethiopia (n = 157; 79 girls). Just over half of the sample (50.9%) had z-scores of − 2SD or below on at least one measure, indicating an elevated risk of morbidity/mortality; 30% were at or below − 2SD on two or more measures. We used hierarchical linear regression with random intercept analysis to model WAZ and HAZ. Siblings and crop sales significantly decrease WAZ while electricity, agriculture, and polygyny improve z-scores; however, an interaction between polygyny and siblings indicates negative effects of siblings in polygynous families and positive effects in nonpolygynous ones (adj. R2 = 66.5%). For HAZ, agriculture and electricity are positively associated with z-scores whereas siblings have a negative effect; the interaction term again indicates that effects of siblings vary in polygynous and nonpolygynous families (adj. R2 = 74.2%). A mediation model exploring the role of weight in height outcomes suggests not only that WAZ has direct effects on HAZ but also that effects of electricity and agriculture on HAZ are partially mediated by WAZ. Our findings indicate that WAZ and HAZ are primarily affected by shared variables, but effects of siblings vary by polygyny status. Long-term outcomes (HAZ) among Sidama children would likely benefit from interventions focused on stabilizing WAZ across family members. (shrink)

This study analyzes the influence of grandmothers’ household residency on the presence of low height-for-age and excessive fat, waist circumference, and sum of triceps and subscapular skinfolds in a sample of 247 6- to 8-year-old urban Maya children from Yucatan, Mexico. Between September 2011 and January 2014, we obtained anthropometric and body composition data from children and mothers, as well as socioeconomic characteristics of participants and households. Grandmothers’ place of residence was categorized as either in the same household as their (...) grandchildren or in separate households. Multiple logistic regression models were used to analyze the association between grandmothers’ residency and outcome variables. Models were adjusted for maternal anthropometric characteristics and the following socioeconomic variables: family size, location, maternal education, monthly family income, and household crowding. Models showed that the presence of grandmothers in their grandchildren’s households was not associated with any of the outcome variables. In contrast, larger family size, overcrowding in the household, and lower family income predicted low height-for-age in children. Larger family size decreased the risk for being overweight based on the three parameters of body composition. Overcrowding in the household increased the risk for greater skinfolds thickness, while low family income increased the risk for higher fat mass index. The residency of grandmothers in their adult daughters’ households is not significantly associated with the outcome variables in this sample of urban Maya families. Instead, maternal anthropometric characteristics and socioeconomic conditions of the family have a greater influence on the overall growth of children. (shrink)

Alloparenting, wherein people provide care to children who are not their biological offspring, is a key aspect of human child-rearing. In the Pacific, many children are adopted or fostered by custodial alloparents even when both biological parents are still alive. From a behavioral ecology perspective, such behaviors are puzzling: why parent someone else’s child at your expense? Furthermore, little is known about how these arrangements are made in Pacific Islander societies today, who provides care, and what kinds of outcomes fostered (...) children experience. A better understanding of these proximate factors may help reveal the ultimate drivers behind custodial alloparenting. Here, we report findings from a survey carried out with the caregivers of 282 children in rural areas of Vanuatu, an island nation in Melanesia. Most fostered and adopted children lived with relatives such as aunts, uncles, and grandparents (87.5%) rather than unrelated caregivers, with a strong preference for maternal kin. The most common reasons for these arrangements were that the parents had separated (16.7%), were engaging in labor migration (27.1%), or a combination of both (27.1%). Results for investment in children’s education and their educational outcomes were mixed, although children removed from crisis situations did more poorly than children removed for aspirational reasons. Our findings suggest that custodial alloparenting helps families adapt to socioeconomic transitions and changing marriage practices. Outcomes may depend on a range of factors, such as the reason children were transferred out of the natal home to begin with. (shrink)