AI quiz split_17-22.pdf

234 ChALLENGES OF PARENTiNG AND KiNShiP the father would be in the younger generation, than for the mother’s father. If this hypothesis receives further empirical support, it would suggest that grandparents might be sensitive either to prevailing rates of infdelity or to personal circumstances tha...

234 ChALLENGES OF PARENTiNG AND KiNShiP the father would be in the younger generation, than for the mother’s father. If this hypothesis receives further empirical support, it would suggest that grandparents might be sensitive either to prevailing rates of infdelity or to personal circumstances that might jeopardize the genetic link between them, their children, and their grandchildren. An alternative hypothesis was suggested by Professor Bill von Hippel (personal communication, October 10, 2002). He proposed a competing explanation that centers on the presence or absence of other outlets for investing one’s resources. Specifcally, paternal grandmothers are also likely to be maternal grandmothers, since they are likely to have at least one daughter who has children. Thus, they have a very secure alternative outlet for investment—in their daughter’s children—and so invest less in their son’s children. In contrast, maternal grandfathers have no better outlet for investment than in their daughter’s children and so channel more resources toward those children than do paternal grandmothers. In essence, maternal grandfathers have a reliable outlet through their daughter’s children, whereas paternal grandmothers might cut back on investing in their son’s children because they have their daughter’s children as a more secure outlet. The beauty of this hypothesis is that it can be easily tested: Paternal grandmothers should devote fewer resources than maternal grandfathers only when paternal grandmothers also have daughters. When they have only sons, in contrast, paternal grandmothers should be roughly comparable in the resources they allocate. Preliminary support for this hypothesis has been found in a study that examined how emotionally close 767 individuals felt to each of their four grandparents (Laham, Gonsalkorale, & von Hippel, 2005), although another study with a smaller sample size failed to fnd this efect (Bishop, Meyer, Schmidt, & Gray, 2009). The grandparental investment hypothesis also was tested by Harald Euler and Barbara Weitzel, who studied a sample of 1,857 participants recruited in Germany (Euler & Weitzel, 1996). Of this sample, 603 cases were selected using the criterion that all four grandparents had to be living at least until the participant reached the age of 7. Subjects were asked how much each grandparent had gekummert, a German verb that has both a behavioral and cognitiveemotional meaning. It includes “(1) to take care of, to look after, and (2) to be emotionally and/ or cognitively concerned about” (Euler & Weitzel, 1996, p. 55). The results of the German sample showed precisely the same pattern as the frst study of U.S. grandchildren. The maternal grandmother—the relationship showing no relational uncertainty— was viewed as having the most gekummert. The paternal grandfather—the most genetically uncertain of all—was viewed as having the least gekummert. As in the U.S. study, the MoFa showed more investment than the FaMo. The latter fnding is especially interesting because it rules out a potential alternative explanation: that perhaps women in general are more likely to invest than men, a sex diference that might extend to relationships with grandparents. The fndings from both studies contradict this alternative. In each study, the maternal grandfathers invested more than the paternal grandmothers. In sum, the general expectation of a sex diference in investment cannot explain the fact that grandfathers, under some circumstances, invest more than grandmothers. Essentially the same patterns of grandparental solicitude have now been replicated in Greece, France, and Germany (Euler, Hoier, & Rohde, 2001; Pashos, 2000), and in a sample of older grandparents residing in the United States (Michalski & Shackelford, 2005). When a grandchild dies, the grief experienced by the grandparents shows the same pattern, with maternal grandmothers grieving the most and paternal grandfathers grieving the least (Littlefeld & Rushton, 1986). People generally have the best relationship with their maternal grandmother and the least good relationship with their paternal grandfather (Euler et al., 2001). A Study of 831 people from the Netherlands found that maternal grandmothers were signifcantly more likely than paternal grandfathers or grandmothers to maintain frequent faceto-face contact, even as the physical distance between grandchild and grandparent increased (Pollet, Nettle, & Nelissen, 2007). The authors conclude that “maternal grandmothers do [literally] go the extra mile” (2007, p. 832)—fndings that are robust across cultures (Euler, 2011; Tanskanen, Rotkirch, & Danielsbacka, 2011). There is some evidence that the maternal grandmother’s investment makes a diference in the survival of grandchildren. A study of families living during the years of 1770 to 1861 in Cambridgeshire, England, found that maternal grandmother’s survival, but not the survival of any 8 PRObLEMS OF KiNShiP of the other grandparents, increased the odds that the grandchildren would survive (Ragsdale, 2004). Interestingly, this efect occurred through two paths. First, the MoMo’s survival increased the odds of the grandchild’s survival as a result of the increased survival of the mother. Second, even controlling for the mother’s survival, the MoMo’s survival increased the odds of the grandchild’s survival. These results support the hypothesis that maternal grandmothers invest more in grandchildren than do other grandparents—support that makes a real diference in the currency of survival. A meta-analysis of 17 studies also found that presence of maternal grandparents increased the survival rates of grandchildren (Strassmann & Garrard, 2011). One explanation for why grandmothers help has been called the grandmother hypothesis: The idea that women evolved such a long post-menopausal lifespan precisely because grandparental investment (e.g., help, care, food, wisdom) enabled women to increase their inclusive ftness (Hawkes, O’Connell, Blurton Jones, Alverez, & Charnov, 1998; Williams, 1957). As a complement to the grandmother hypothesis, Kuhle (2007) proposed the absent father hypothesis—the idea that because men die at a younger age than their mates and—if they live, they sometimes leave their aging partners to mate with younger partners—it would have been benefcial for women to stop reproducing directly and instead invest in existing children and grandchildren. Evidence that grandmothers do have benefcial efects on grandchildren, especially under harsh or risky circumstances, has been cumulating, although the issue of whether these efects explain why women live so long after reaching menopause remains hotly debated (see Coall & Hertwig, 2010, and associated commentaries). Many questions remain unanswered by this research. How do prevailing rates of infdelity in each generation afect the psychology of grandparents’ investment? Do grandparents monitor the likelihood that their sons might be cuckolded and shift their investment accordingly? Do grandparents scrutinize grandchildren for their perceived similarity to them as part of their decision making about investing in those grandchildren? These questions about the evolutionary psychology of grandparental investment will likely be answered within the next decade. For now, we can conclude that fndings from several diferent cultures support the hypothesis that grandparents’ investment is sensitive to the varying probability that genetic relatedness might be severed by paternity uncertainty in each generation. (See Box 8.2 for a parallel discussion on investment by aunts, uncles, and cousins.) 8.2 Investment by Aunts, Uncles, and Cousins Selection should favor adaptations that result in investing in kin as a function of genetic relatedness. Expected relatedness is a function of two factors: (1) genealogical linkage (e.g., sisters are more closely related than uncles and nephews) and (2) paternal uncertainty. In this chapter, we have looked at evidence suggesting that as paternal uncertainty increases through the paternal line, investment in grandchildren decreases. Is this efect limited to grandparents’ investment, or does the logic extend to other kin relationships, such as aunts and uncles? According to this logic, maternal aunts (sisters of the mother) should invest more than paternal aunts (sisters of the father). Similarly, maternal uncles (brothers of the mother) should invest more than paternal uncles (brothers of the father). Paternity certainty, and hence genetic relatedness, should be highest on average through the maternal line. Genetic relatedness should be lowest on average through the paternal line. A team of researchers studied 285 U.S. college students, all of whom reported that both of their biological parents were living (Gaulin, McBurney, & Brakeman-Wartell, 1997). Each participant was asked to rate a series of questions using a seven-point scale: (1) “How much concern does the maternal (paternal) uncle (aunt) show about your welfare?” (2) If you have both a maternal and a paternal uncle (aunt), which one shows more concern about your welfare?” (1997, p. 142). The researchers selected the phrase “concern about your welfare” so that participants would think broadly about the various types of benefts they might receive. Findings support the hypothesis that maternal aunts invest more than paternal aunts and maternal uncles invest more than paternal uncles. Two main efects are noteworthy. First, there is a main efect for sex: Aunts tend to invest more than uncles, regardless of whether they are maternal or paternal. Second, maternal aunts and uncles tend to invest more than paternal aunts and uncles—the predicted laterality efect. According to the researchers, these two efects are likely to have diferent causes. They suggest that the sex efects (aunts invest more than uncles) occur because men tend to invest surplus resources into mating opportunities, whereas women do not. The laterality efect, in contrast, has a diferent explanation, based on the probabilities of paternity 235 ChALLENGES OF PARENTiNG AND KiNShiP 236 uncertainty that occur through the male line. Uncertainty of paternity, and hence a lower likelihood of genetic relatedness, is the best explanation for the evolution of psychological adaptations that lead to the investment decisions of aunts and uncles. When paternity certainty is guaranteed, as when you are a sibling of the mother of your niece or nephew, you will invest a lot. Aunts who are themselves childless are especially likely to invest in their nieces and nephews (Pollet, Kuppens, & Dunbar, 2006; Pollet et al., 2007). When paternity is uncertain, as when you are a sibling of the father of your niece or nephew, you are likely to invest less. The same logic can be used to predict altruism toward cousins (Jeon & Buss, 2007). People should be most willing to help their mother’s sister’s (MoSis) children, who have the highest probability of genetic relatedness, and least willing to help their father’s brother’s (FaBro) children, who have the lowest probability of genetic relatedness. Helping toward father’s sister’s (FaSis) and mother’s brother’s (MoBro) children should fall in between. A study to test these predictions asked people the following: “As you make your way throughout the city you walk past a building that is blazing with fames. You instantly realize that the building has been housing a meeting attended by your cousin ___ (fll in the initials). Your cousin ___ in the rapidly burning building badly needs your help, yet entering the building to save him or her would risk injury to you” (Jeon & Buss, 2007, p. 1182). As shown in Figure 8.3, willingness to help the diferent categories of cousins occurs precisely as predicted. The results support the hypothesis that humans have adaptations sensitive to varying probabilities of genetic relatedness; in this case, through varying probabilities of paternity uncertainty. Findings show that people express a greater willingness to help cousins with a higher likely degree of genetic relatedness (e.g., cousins through one’s mother’s sister) than cousins with a lower likely degree of genetic relatedness (e.g., cousins through one’s father’s brother). In sum, genetic relatedness, as predicted by inclusive ftness theory, appears to be a major factor in investment in relatives. When genetic relatedness is jeopardized through paternity uncertainty, investment falls of. This efect is robust across diferent sorts of relationships, including those with aunts, uncles, grandmothers, grandfathers, and cousins (Pashos & McBurney, 2008). Figure 8.3 Altruism Toward Cousins Source: Jeon, J., & Buss, D. M. (2007). Altruism toward cousins. Proceedings of the Royal Society of London (Figure 8.2). A Broader Perspective on the Evolution of the Family What is a family? Various disciplines defne this entity diferently, and social scientists have not reached frm agreement about what constitutes a family (Emlen, 1995). Sociologists ofen emphasize the childrearing function of the family, defning families as groups of adults living together, bearing the responsibility for producing and raising children. Anthropologists, in contrast, tend to stress kinship, defning families as groups of parents, unmarried children, and sometimes extended kin through which lines of descent can be traced. Evolutionary biologist Stephen Emlen defnes families as “those cases where ofspring continue to interact regularly, into adulthood, with their parents” (Emlen, 1995, p. 8092). He distinguishes two types of families: (1) simple families, a single parent or conjugal pair in which only one female reproduces (e.g., a mother and her pre-reproductive ofspring), and (2) extended families, 8 PRObLEMS OF KiNShiP groups in which two or more relatives of the same sex may reproduce. Notice that the presence of a breeding male is not essential to the defnition of family. When the male is present, however, the family is called biparental because both the mother and the father share some responsibility for parenting. When the male is absent, the family is called matrilineal because the females (or the female and her female relatives) are responsible for parenting. One defning feature of all families is that ofspring continue to live with their parents past the age at which they are capable of reproducing on their own. Families are so much a fact of life for humans that we take their existence for granted. The astonishing fact, however, is that a mere 3 percent of all bird and mammalian species form families (Emlen, 1995). Why are families so rare? Why do most ofspring throughout the animal world leave the nest as soon as evolution has made them biologically capable of doing so, and so few remain with their parents past sexual maturity? The most likely reason is that remaining in the parental nest (or delaying departure from the nest) carries a tremendous reproductive cost. In simple families, ofspring do not reproduce while living at home. In extended families, however, parents will often actively suppress the reproduction of their ofspring (e.g., by interfering with mating attempts). In both cases, the ofspring sacrifce reproduction by delaying departure from the family unit. Families thus infict two primary costs on ofspring: (1) Reproduction is delayed and sometimes directly suppressed (perhaps the heaviest cost), and (2) competition for resources such as food is concentrated rather than dispersed, making life more challenging for both parents and ofspring. The only way families can evolve is when the reproductive benefts of remaining in the family are so great that they outweigh the heavy costs of forgoing early reproduction. Two major theories have been proposed to explain the evolution of families. The frst is the ecological constraints model. According to this theory, families emerge when there is a scarcity of reproductive vacancies that might be available to the sexually mature ofspring. Under these conditions, both the cost of staying within the family and the benefts of leaving are low. The heavy cost of staying within the family—delayed reproduction—vanishes because early reproduction is not possible owing to a lack of reproductive vacancies (i.e., resource niches that provide the opportunity for reproduction). The second theory is the familial benefts model. According to this theory, families form because of the bounty of benefts they provide for ofspring. These benefts include (1) enhanced survival as a result of aid and protection from family members, (2) an enhanced ability to compete subsequently, perhaps by acquiring skills or greater size and maturity as a result of staying at home, (3) the possibility of inheriting or sharing the family territory or resources as a result of staying at home, and (4) inclusive ftness benefts gained by being in a position to help and be helped by genetic relatives while staying at home. Emlen (1995) synthesizes these two theories into one unifed theory of the origins of the family. His theory of family formation has three premises. First, families form when more ofspring are produced than there are available reproductive vacancies to fll. This premise stems from the ecological constraints model. Second, families will form when ofspring must wait for available reproductive vacancies until they are in a good position to compete for them. Third, families will form when the benefts of staying at home are large—in the form of increased survival, increased ability to develop competition skills, increased access to familial resources, and increased inclusive ftness benefts. Emlen’s theory of the family is thus a synthesis of the ecological constraints and the family benefts models. Several predictions follow from Emlen’s theory. The frst set of predictions involves the family dynamics of kinship and cooperation. Prediction 1: Families will form when there is a shortage of reproductive vacancies but will break up when the vacancies become available. Families will be unstable, forming and breaking up depending on the circumstances. This prediction has been tested in several avian species (Emlen, 1995). When new breeding vacancies were created where there previously had been none, mature ofspring “few the coop” and left home to fll those vacancies, splitting apart an intact family. Sexually mature children who are not yet in a position to compete successfully for mates or are not in a resource position to maintain a home on their own will tend to remain with their family unit. 237 ChALLENGES OF PARENTiNG AND KiNShiP 238 Prediction 2: Families that control many resources will be more stable and enduring than families that lack resources. Among humans, the expectation would be that wealthy families will be more stable than poor families, especially when there is a chance that the children might inherit the parental resources or territory. Children coming from high-resource homes are predicted to be especially choosy about when and under what conditions they decide to leave home. By sticking around, mature children may inherit the wealth, so wealthier families should show greater stability over time than poor families. Among many species of familial birds and mammals, ofspring do indeed sometimes inherit their parents’ breeding place. Davis and Daly (1997) provide empirical support for this prediction by fnding that high-income families are indeed more likely to maintain social ties with their extended kin than are low-income families. Prediction 3: Help with rearing the young will be more prevalent among families than among comparable groups lacking kin relatives. A sister or brother, for example, might assist in raising a younger sibling, providing a key inclusive ftness beneft by living with the family. They are “helpers at the nest.” A study of the Hadza hunter-gatherers of Tanzania found support for this prediction—closely related females (sometimes called “allomothers”) spent the largest percentage of time holding and caring for the children of their relatives (Crittenden & Marlowe, 2008). Prediction 4: When a breeder is lost because of death or departure, family members will get into confict over who will fll the breeding vacancy. The loss of a parent opens up a new vacancy, creating the perfect opportunity for ofspring to inherit the natal resources. The higher the quality of the vacancy, the more competition and confict there will be to fll it. Among red-cocked woodpeckers, for example, in each of 23 cases of the death of a father, one of the sons took over the breeding role, and the mother was forced to leave. Among humans, an analogous situation might occur if a father died and left behind a large inheritance. Children often engage in lawsuits concerning claims to an inheritance, and claims made by genetically unrelated individuals (e.g., a mistress of the father to whom he left resources) are often challenged (Smith et al., 1987). Prediction 5: The loss of an existing breeder and replacement by a breeder who is genetically unrelated to family members already present will increase sexual aggression. When a mother is divorced, widowed, or abandoned and she remates with an unrelated male, the strong aversions against incest are relaxed. Stepfathers might be sexually attracted to stepdaughters, for example, thus pitting the mother and daughter against each other in intrasexual rivalry. Among a variety of avian species, aggression between sons and stepfathers is common, since these unrelated males are now sexual competitors (Emlen, 1995). Among humans, having a stepfather in the home puts girls, both prepubescent and postpubescent, at a greater risk of sexual abuse (Finkelhor, 1993). Emlen’s theory, in sum, generates a rich set of testable predictions. Many of these predictions have received support from avian, mammalian, and primate species, but others remain to be tested. Especially intriguing is their applicability to human families. Critique of Emlen’s Theory of the Family Evolutionary psychologists Jennifer Davis and Martin Daly have criticized Emlen’s theory, ofering several useful modifcations as well as empirical tests of a few key predictions (Davis & Daly, 1997). Davis and Daly ofer three considerations that provide a unique context for examining human families: (1) Human families might remain together because of competition from other groups, such that remaining in a large kin-based coalition is advantageous in such group-on-group competition (see Webster, 2008); (2) humans engage in extensive social exchange based on reciprocal altruism with non-kin; and (3) nonreproductive helpers, such as post-menopausal women, have little incentive to encourage their ofspring to disperse, which might help to stabilize families. 8 PRObLEMS OF KiNShiP 239 These three considerations could afect the logic of Emlen’s predictions. Consider prediction 1, which suggests that families will dissolve when acceptable breeding opportunities become available elsewhere. If a woman is post-menopausal and hence incapable of further reproduction, it would clearly not be benefcial for her to abandon her family and the help she could provide when a breeding vacancy arose elsewhere. Because she is post-menopausal, she cannot exploit the breeding vacancy. Rather, it would pay to remain with her kin and continue to provide help. Another modifcation pertains to the fact that humans engage in extensive social exchange. Consider prediction 3: Help with rearing the young will be more prevalent among families than among comparable groups lacking kin relatives. Women often form friendships with non-kin in which they engage in reciprocal help with childrearing (Davis & Daly, 1997). Prediction 3 could be modifed—unreciprocated help with rearing the young should be more prevalent among families than among comparable groups lacking kin relatives. In summary, several of Emlen’s predictions need modifcation by considering factors unique to humans, such as extensive patterns of reciprocal alliances (see Chapter 9) and the prolonged post-menopausal period of women. Across species, families are exceedingly rare. Given current social interest in “family values,” evolutionary psychology has something to ofer by illuminating the conditions under which families remain stable or fall apart. In the next decade, researchers will undoubtedly test these predictions and uncover a rich array of evolved psychological mechanisms—those involving cooperation as well as confict—designed to deal with the varying adaptive problems posed by families. The Dark Side of Families We ofen think of families as harmonious social sanctuaries that involve the benevolent transfer of resources, protection, information, and status. Indeed, even in evolution biology, the “classical” view of the family was of a harmonious unit of cooperating individuals that functioned to maximize the number of surviving ofspring (Parker, Royle, & Hartley, 2002). Nonetheless, well-developed evolutionary theories over the past three decades have overthrown this harmonious view and point to a darker side of family life: pervasive conficts over resources, perhaps most centrally over the parental resources. There are three fundamental sources of confict within families (see Figure 8.4). The frst is sibling confict. Within the same family, siblings compete with one another for access to parental Figure 8.4 Three Major Forms of Confict Within Families Source: Modifed from Parker, G. A., Royle, N. J., & Hartley, I. R. (2002). Intrafamilial confict and parental investment: A synthesis. Philosophical Transactions of the Royal Society of London B, 357, 295–307. This fgure shows three major types of confict within families: sibling confict over parental resources, parent–ofspring confict, and confict between the mother and father.