Importance of Maternal Grandmother
KeywordsMaternal Grandmother Paternal Grandmother Maternal Grandfather Grandchild Care Paternal Grandfather
If one asks people which of their four grandparents provided the most care for them when they were a child or to which grandparent they feel closest, the most people will answer the maternal grandmother.
Indeed, many research studies found that the intensity of caregiving by the four grandparents is not the same but regularly different. In most urban societies, grandmothers typically invest more in grandchildren than grandfathers, and maternal grandparents invest typically more than paternal. Thus, grandparental caregiving (i.e., their grandchild care, investment of resources, solicitude, involvement, and contact frequency) follows the asymmetric pattern: maternal grandmother provides on average the most caregiving for grandchildren, followed by the maternal grandfather and the paternal grandmother, and the paternal grandfather provides the least caregiving (Smith 1988; Euler and Weitzel 1996; Salmon 1999; Pashos 2000; Pashos and McBurney 2008; Danielsbacka et al. 2011; Pashos et al. 2016). The same asymmetric pattern exists also for emotional closeness: on average, grandchildren are closest to the maternal grandmother and least close to the paternal grandfather (Russell and Wells 1987; Laham et al. 2005; Pashos and McBurney 2008; Pashos et al. 2016). The asymmetric pattern cannot be explained by the different survival chance or age of the grandparents that follows the same order (the maternal grandmother is on average the youngest; the paternal grandfather is the oldest), as analyses have shown (Euler and Weitzel 1996; Pashos 2000). Also residential distance, which in general strongly affects the grandparental caregiving, does not explain the caregiving biases. Same is true for other potential confounding factors which are however only inconsistently found, such as birth order, parent age, and grandchild age (for an overview, see Euler 2011).
Also in anthropological studies that deal with the evolution of grandparenthood, the maternal grandmother plays a central role. The classical grandmother hypothesis, also called prudent mother hypothesis, assumes that menopause has evolved in humans to stop the risky female reproduction in older age, in favor of investing in already existing children or grandchildren. According to Kristin Hawkes’ newer version of the grandmother hypothesis, grandparenting along with longevity evolved through the grandmothers, who helped their daughters with provisioning the offspring (Hawkes et al. 1998). A number of studies using medical health data (Sear et al. 2000) or historical data (Sorenson Jamison et al. 2002; Beise 2005; Ragsdale 2004) found support for this view. These studies found lower child mortality or a better nutritional status in families where the maternal grandmother was present. In a German study, using historical data from Frisia, the paternal grandmother had even a negative effect on child survival (Voland and Beise 2002). However, other research studies revealed a rather mixed picture. Although most studies showed indeed positive effects for maternal grandmothers regarding child survival, some studies also found positive effects for paternal grandmothers, maternal grandfathers, or other kin, and some studies could not find a particular significance for any grandmothers (Sear and Mace 2008; Strassmann and Garrard 2011). Leonetti et al. (2005), for example, found a positive effect of the maternal grandmother, for maternal health, and child survival among the matrilineal Khasi. However, among the patrilineal Bengali, they found a positive effect of the paternal grandmother on their daughter-in-law’s fertility. From an evolutionary point of view, these mixed results might however very well represent different reproductive strategies. The maternal grandmother is biologically related to both her daughter and her grandchildren and hence also interested in her daughter’s health, whereas the mother-in-law’s reproductive interest is to invest in further grandchildren, however, not in her genetically unrelated daughters-in-law.
Maternal grandmothers were often found to be related to lower child mortality and this has been usually associated with their grandchild investment. However, cross-culturally they are not always the most important kin investors. In patrilocal societies, for example, maternal grandmothers do not live close to their grandchildren. Furthermore, many grandmothers are already deceased when grandchildren grow up. Some researchers therefore criticized the grandmother hypothesis in general, stating that the role of grandmothers may be overestimated. Their research results showed the importance of males for the provision of food and not the importance of grandmothers (Hill and Hurtado 2009). As an alternative for the grandmother hypothesis, also a patriarch hypothesis was proposed that assumes the evolution of longevity through males and not through females (Marlowe 2000).
Nevertheless, there is a relatively broad scientific consensus that extended kin members such as grandparents can be significant family helpers. Compared to other species, humans have a prolong childhood, and it requires many resources to raise children to adulthood. Thus, in an ancestral environment, additional family helpers appear to be essential for the mother. Because in mammals most frequently the mother is the only caregiver, these additional offspring-care helpers are often called allomothers in biology, i.e., individuals other than the mother providing childcare. Anthropological research in traditional societies has shown that these caregivers can be typically fathers, older siblings and grandparents, or any other related or unrelated adults (Crittenden and Marlowe 2008; Kramer 2010). Sarah Hrdy (2005), moreover, argued that humans could be classified as cooperative breeders. In a Pleistocene environment, two parent alone are not sufficient for bringing up offspring. Humans are rather characterized by a network of kinship members providing allomaternal assistance. In her view, help from fathers may be important but unreliable. For Hrdy, female helpers are even more important than male helpers; the most beneficial allomothers are, however, experienced elderly females, especially the maternal grandmothers.
For the consideration of maternal grandmothers as important caregiving helpers, not only nutrition and survival of infants should be taken into account. Also, help with childcare itself (Crittenden and Marlowe 2008) or to take responsibilities for children is already an important offspring investment. On the Trobriand islands, for example, it has been found that it is most often the maternal grandmother or other matrilineal kin (i.e., maternal aunts), who adopt children who became orphans (Schiefenhövel and Grabolle 2005). Also in Western countries, fostering roles were typically most frequently taken on by maternal grandmothers (Perry et al. 2014).
Paternity Certainty Hypothesis Explanation
A mother always knows when a child is hers, a father does not. The average degree of relatedness between a grandparent and a grandchild is r = 0.25, or, in other words, 25%. According to the rules of kin selection, under identical framework conditions, all grandparents should thus invest equally in grandchildren. However, due to the male uncertainty of relatedness in the family lineages, the average degree of relatedness to the grandchildren can vary. Therefore, Smith (1988) predicted and found that grandparental investment in grandchildren should be biased: (1) Grandmothers should invest in grandchildren more than grandfathers because of the grandfathers’ paternity uncertainty. (2) Grandparents should invest more in daughters’ children than in sons’ children (i.e., invest more as maternal grandparents than as paternal grandparents) because of the sons’ paternity uncertainty. (3) In combination this means, grandparental investment in grandchildren should follow the order: maternal grandmother (highest investment), maternal grandfather and paternal grandmother (being in the middle), and paternal grandfather (lowest investment, because two times affected by paternity uncertainty).
Russell and Wells (1987) presumed the same differences when they measured in a questionnaire study students’ feelings of closeness to parents and grandparents. The authors tried to estimate the level of paternity confidence by equating the measured differences in closeness mathematically with a factor for paternity uncertainty. In so doing, they calculated an average paternity confidence level of p = 0.874. In other words, they estimated 12.6% paternity uncertainty. Gaulin et al. (1997) used a similar method and estimated the paternity uncertainty between 9% and 17% for the grandparental caregiving results of Euler and Weitzel (1996). Because, the paternity uncertainty in the Western world was often estimated at that level then, the paternity certainty explanation became quickly popular. Newer studies, however, have estimated the level of actual paternity uncertainty in Western societies much lower, presumably less than 1–3% (Anderson 2006). Moreover, other researchers could not confirm an influence of actual paternity certainty in a society on measured caregiving biases. They therefore interpreted the universal asymmetric caregiving pattern as a reflection of paternity certainty in the environment of evolutionary adaptedness (EEA) rather than by current paternity confidence (McBurney et al. 2002). Reluctance in child caregiving might also be a result of a general tendency of mistrusting men’s paternity, which has evolved in order to avoid misinvestment in genetic unrelated individuals. Reluctance in investing in patrilineal descendants might be a result of this general tendency of mistrusting paternity.
Although direct kin recognition mechanisms for detecting kinship such as phenotype matching might exist in humans, from a proximate point of view, the caregiving differences between the grandparents appear to be too great to be only explained by actual paternity uncertainty. Some authors thus also have expanded the paternity certainty explanation by other explanations such as a sex-specific reproductive strategy which explains an additional bias in favor of daughters’ children (Euler and Weitzel 1996; Euler 2011).
Stronger Matrilineal Family Ties as Explanation
In explaining why in particular maternal grandmothers are the most prominent caregivers, however, it is not necessary to assume that differential investment by grandparents is triggered by underlying mechanisms of detecting the certainty of relatedness to a grandchild. The caregiving biases can also be interpreted on a proximate level as a result of stronger matrilineal family ties, which create pathways for discriminative or preferential kin investment (Pashos 2000).
Research results show that women generally have closer ties to their families than men have to theirs (Salmon 1999). Thus, matrilineal family connections are stronger than patrilineal. In particular, the strong relationship between mothers and maternal grandmothers was found to reinforce biased caregiving to a significant degree (Chan and Elder 2000; Pashos 2000). However, also in general, the grandparent-parent and the grandparent-grandchild closeness were found to be interrelated (Michalski and Shackelford 2005). Moreover, the quality of the grandparent-parent relationship can explain the asymmetric grandparental caregiving to a great extent (Monserud 2008; Pashos and McBurney 2008). In addition, the relationship dyad between the daughter-in-law and the mother-in-law is on average the least good of all parent and grandparent relationships (Euler et al. 2009; Lee et al. 2003). This additionally increases the matrilateral bias. If, however, the relationship between the mother and her mother-in-law (i.e., the paternal grandmother) was good, grandchildren were found to have closer feelings to their paternal grandmother (Monserud 2008).
These research results fit very well with the proximate explanation of stronger matrilineal family ties as cause and not as result of asymmetric caregiving. Because the relationship of a woman to her parents, especially to her mother, is more intimate than to her parents-in-law, and is more close compared to a man’s relationship to his parents, a mother brings her children into closer contact with her parents than her husband with his parents. A frequent contact between grandparents and grandchildren enables the development of social closeness which allows or triggers the emergence of emotional closeness and grandparental caregiving through evolutionary mechanisms (Pashos and McBurney 2008). Therefore, caregiving by maternal grandparents, especially by the maternal grandmother, is stronger than that by paternal grandparents.
In the social sciences, similar explanations have been proposed and discussed to explain the asymmetric grandparent-grandchild relationships, however, usually ignoring or rejecting evolutionary influences on human kinship behavior. The parents, in particular the mothers, are seen as mediators or gatekeepers, who can build a bridge or also a barrier between the grandparents and the grandchildren (Chan and Elder 2000). Alternatively, women have been described as kin-keepers, who hold the family networks together. In this view, matrilineally biased intergenerational relationships are seen as a result of the female kin keeping, in which gender is not only relevant for parents but also for grandparents and grandchildren (Dubas 2001; Monserud 2008).
Maternal Grandmother and Divorce
The caregiving by grandparents who live together as a couple, as well as their contact frequency with grandchildren, is higher than by grandparents who are divorced. This effect is in particular true for the grandfathers (Euler and Weitzel 1996; King 2003), whose grandchild caregiving might be positively influenced by the coresident grandmothers (Gaulin et al. 1997). Maternal grandmothers, however, play a special role when it comes to a separation of a grandparent couple. Pashos et al. (2016) found that divorced grandmothers, as maternal grandmothers, did not show a reduction of kin investment in daughters’ children, however, as paternal grandmothers, did invest less in sons’ children. This means that the caregiving by divorced grandmothers was even more biased in favor of their daughters’ children; in other words, the matrilateral bias was greater. Interestingly, when grandmothers were remarried after divorce, their new husbands mirrored this discriminative matrilateral behavior of the grandmothers pretty strongly (Pashos et al. 2016).
The asymmetric grandparental investment pattern is very reliable to measure. It appears to be quite universal in all urban Western societies. However, in rural or more traditional societies also cultural variation in the asymmetric order of grandparental caregiving has been found. In rural mainland Greece, a traditional patrilocal society, paternal grandparents, especially paternal grandmothers, provided more caregiving than maternal grandparents, whereas among urban Greeks, the universal matrilineal caregiving pattern was found (Pashos 2000). Also in the USA, for rural farmers in Iowa, it has been found that grandchildren had more frequent contact with their paternal grandparents and received more help from them as compared to grandchildren from urban Southern California (King et al. 2003). Paternal grandparents who take on the duties of caregiving have also been documented for further countries, for example, rural China (Kaptijn et al. 2013).
Even if one assumes a higher paternity certainty for patrilocal societies where mothers-in-law can exert control over daughters-in-law, the paternity certainty hypothesis can only explain matrilineal biases in kin investment. A patrilateral or patrilineal bias in itself cannot be explained using this theory, because in a society with high paternity certainty, all asymmetric biases should disappear (Pashos 2000). Therefore, additional evolutionary explanations for the investment in sons and grandsons must be proposed, such as the Trivers-Willard hypothesis (Pashos 2000; Pashos and McBurney 2008).
Maternal grandmothers play a prominent role as kin caregivers in urban modern societies. In traditional societies, however, also paternal grandparents can take the place of the maternal grandmother as most important caregivers. Differing cultural rules can superimpose the strong, universal matrilineal family ties. Anthropological studies have shown the need for family helpers in rearing and raising children, what highly likely also led to the evolution of grandparenthood. The mother’s mother appears to be especially predestined for this role, because she has not only a reproductive interest in helping her grandchildren but also in helping her daughter to whom she is related, as well.
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