Evolutionary Psychology - Problem of Kinship PDF

PSYC205 Evolutionary Psychology Problem of Kinship Edison Tan Evolutionary Psychology Singapore Management University Recall: Inclusive Fitness Theory Altruism refers to a behavior or an act that (a) incurs a cost to self in order to...

PSYC205 Evolutionary Psychology Problem of Kinship Edison Tan Evolutionary Psychology Singapore Management University Recall: Inclusive Fitness Theory Altruism refers to a behavior or an act that (a) incurs a cost to self in order to The Hamilton Rule Altruism is favored by natural (b) provide benefits to another person. selection when: Cost and benefits are measured in reproductive currencies (i.e., differential odds of reproductive success) rB >C Natural selection will favor altruism (e.g., parental investment) between the altruist and target (e.g., parent and child, r = 0.5) if fitness benefits to kin are r – proportion of shared genes (in probability) more than the fitness cost to the altruist (B = 2, C =1). B – fitness benefits in terms of If you are to lose your life to save family members, you are more how many offspring are likely to do so if you will save three sibling siblings [rB >C = (0.5)(3) > produced 1] than one sibling [rB Maternal Grandfather/Paternal Grandmother> Paternal Grandfather Edison Tan Evolutionary Psychology Singapore Management University Grandparents and grandchildren DeKay(1995,). Grandparental investment and the uncertainty of kinship. …why do maternal grandfathers invest more than paternal Paper presented to Seventh Annual Meeting of the Human Behavior and Evolution Society grandmothers when they face identical opportunities to sever genetic links? Paternal grandmothers are also likely to be maternal grandmothers since they are likely to have at least one daughter who has children. What is going on here? Secure alternative outlets 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 Channel more resources toward daughter’s children than do paternal grandmothers. Paternal grandmothers should devote fewer resources than maternal grandfathers only when paternal grandmothers also have daughters. (Laham, Gonsalkorale, & von Hippel, 2005) Rule out the alternate hypothesis that grandparental investment is an extension of parental investment – grandmothers do not always invest more than grandfathers Edison Tan Evolutionary Psychology Singapore Management University Grandparents and grandchildren Absent Father Hypothesis Why do grandmothers even invest at all? Men tend to die at a younger age than their mates, and—if they live, they sometimes leave their aging partners to mate with Grandmother Hypothesis younger partners—it would have been beneficial for women to Menopause served an evolutionary function of ceasing stop reproducing directly and instead invest in existing reproduction to invest in children and grandchildren, children and grandchildren. enabling increased inclusive fitness with declining reproductive value. Edison Tan Evolutionary Psychology Singapore Management University Aunts and Uncles On average, siblings of parents are genetically related to individuals at 0.25 coefficient. How would aunts and uncles invest? Findings from Gaulin et al. (1997) 7-point Likert scale; order of presentation counterbalanced How much concern does the maternal (paternal) uncle (aunt) show about your welfare?” If you have both a maternal and a paternal uncle (aunt), which one shows more concern about your welfare?” Two Main Effects Sex effect – aunts invest more than uncles Men may tend more to invest excess resources into mating efforts than kins Laterality Effect – maternal aunts invest more than paternal aunts, and maternal uncles invest more than paternal uncles. Paternal Uncertainty may sever genetic relatedness Edison Tan Evolutionary Psychology Singapore Management University Cousins On average, cousins are genetically related to individuals at 0.125 coefficient. How would cousins help each other? Findings from Jeon & Buss (2007) Genetic Relatedness and probability of paternal uncertainty predicts kin-altruism between cousins 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). Edison Tan Evolutionary Psychology Singapore Management University  03 Evolution of Families Why do families even exist? Edison Tan Evolutionary Psychology Singapore Management University  Definition of a Family in Evolutionary Sciences Simple Family - a single parent or conjugal pair in which only one female reproduces (e.g., a mother and her pre-reproductive offspring). Extended families - groups in which two or more relatives of the same sex may reproduce. The presence of a breeding male is not essential to the definition of family. When the male is present, 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. Edison Tan Evolutionary Psychology Singapore Management University  The Solitary Sandpiper vs the Black-naped Blue Flycatcher Families are rare Only 3% of avian and mammalian mammalian species form families. Remaining in the parental nest carries a tremendous cost Why so few? In simple families, offspring do Two primary costs on offspring: not reproduce while living at Reproduction is delayed and sometimes directly suppressed home. Competition for resources such as food is concentrated rather In extended families, parents than dispersed, making life more challenging for both parents will often actively suppress and offspring. the reproduction of their Families can only evolve if the benefits of staying with offspring (e.g., by interfering with mating attempts your family outweigh these cost Edison Tan Evolutionary Psychology Singapore Management University  Evolution of Families Ecological Constraints Model Familial Benefit Model Families emerge when there is a scarcity of Family form because family provides immense reproductive vacancies (i.e., resource niches benefit for the offspring that provide the opportunity for reproduction) Enhanced survival as a result of aid and that might be available to the sexually mature protection from family members, offspring within the local ecology. An enhanced ability to compete subsequently, perhaps by acquiring skills or greater size and maturity as a result of staying at home The high cost of delayed reproduction is The possibility of inheriting or sharing the family minimized because early reproduction is not territory or resources as a result of staying at possible anyway due to the lack of home reproductive vacancies. Inclusive fitness benefits gained by being in a position to help and be helped by genetic relatives while staying at home. Edison Tan Evolutionary Psychology Singapore Management University  Emlen’s (1995) Theory of the Family Predictions Rationale Prediction #1: Families will form when there is a shortage of Families are unstable. Sexually mature children who are not in a reproductive vacancies but will break up when the vacancies position to compete for mates or mating resources tend to remain in become available. the family. Those that do will leave the nest when reproductive vacancies are available. Prediction #2: Families that control many resources will be Resourceful families present more of a chance where that the children more stable and enduring than families that lack resources. might inherit the parental resources or territory. Prediction #3: Help with rearing the young will be more An older sister or brother might assist in raising a younger sibling, prevalent among families than among comparable groups providing inclusive fitness benefit to the family. lacking kin relatives. Prediction #4: When a breeder is lost because of death or The loss of a parent opens up a new vacancy, creating the perfect departure, family members will get into conflict over who will opportunity for offspring to inherit the natal resources. The higher the quality of the vacancy, the more competition and conflict there will be fill the breeding vacancy. to fill it. Prediction #:5 The loss of an existing breeder and replacement When a mother is divorced, widowed, or abandoned, and she remates by a breeder who is genetically unrelated to family members with an unrelated male, the strong aversions against incest are relaxed. Stepfathers might be sexually attracted to stepdaughters, for example, already present will increase sexual aggression. thus pitting the mother and daughter against each other in intra- sexual rivalry. Edison Tan Evolutionary Psychology Singapore Management University  Davis & Daly’s (1997) critique on the Theory of the Family Predictions Proposed Modification to the Theory Critique #1: Human families might remain together because of Add on to Prediction #1: competition from other groups, such that remaining in a large Families will stay together if staying together is more beneficial than the kin-based coalition is advantageous in such group-on-group cost imposed by family staying together: competition. When a kin-based coalition faces intensive outgroup threats, the family is a reliable source of help. Critique #2: Humans engage in extensive social exchange based on Add on to Prediction #3: reciprocal altruism with non-kin; Women often form friendships with non-kin and engage in reciprocal help with childrearing. Unreciprocated help with rearing the young should be more prevalent among families than among comparable groups lacking kin relatives. Critique #3: Nonreproductive helpers, such as post-menopausal Add on to Prediction #1: women, have little incentive to encourage their offspring to Families will stay together if staying together is more beneficial than the cost imposed by family staying together: disperse, which might help to stabilize families. If a woman is post-menopausal and hence incapable of further reproduction, it would clearly not be beneficial for her to abandon her family and the help she could provide when a breeding vacancy arose elsewhere. She is better off remaining with her remain with her kin and continue to provide help. Edison Tan Evolutionary Psychology Singapore Management University  Family Conflicts Sibling Conflict Siblings compete with one another for access to parental and grandparental resources. Parent-offspring conflict Parental conflict Parents conflict with how much parental investment each will give to the offspring within the family. It is sometimes beneficial, for example, for one parent to withhold his or her own resources for other avenues of reproduction. Parents might divert resources to his or her own kin and will profit if the other parent provides more resources directly to their offspring. Either parent might use resources to obtain additional mates and consequently produce children who are genetically unrelated to the other parent Edison Tan Evolutionary Psychology Singapore Management University  Discussion Edison Tan Evolutionary Psychology Singapore Management University Is Blood Thicker than Water? Or is the Blood of Covenant Thicker than the Water of the Womb? Genetic relatedness is a robust predictor of the act of altruism – we are far more likely to be helped by genetic relatives over non-relatives. However, altruism is not unique to kinship, much like the case of close friends. Between close friends and family, who do we help, and how much would we help? Edison Tan Evolutionary Psychology Singapore Management University  The Kinship Premium Although emotional closeness In Curry et al. (2013), participants (N =111) completed a self-report questionnaire about their is a psychological marker of willingness to be altruistic (donate a kidney) and genetic relatedness, which in their emotional closeness to 12 family members turn predicts altruistic and friends at 3 increasingly distant positions in behavior, people also feel close their extended social networks. to close friends. Why wouldn’t we help close Altruism was greater for family than friends and greater for more central layers of the network, friends at least just as much as even after controlling for emotional closeness. our kins? In other words, participants were more altruistic towards kin than expected if altruism depended on emotional closeness alone. The Kinship Premium- genetic relatedness has a unique contribution to altruism above and beyond. emotional closeness. Edison Tan Evolutionary Psychology Singapore Management University  The Kinship Premium Other studies have similar findings, using other potentially relevant psychological mediators. Bressan et al. (2009) found that emotional closeness predicts costly help – help that requires self-sacrifice – among step-siblings but not half or full siblings. Emotional closeness was not a significant predictor for either full siblings (β = −0.07, t < 1) or half siblings (β = 0.05, t < 1). On the contrary, emotional closeness was the only significant predictor for step-siblings, explaining 23% of the variance of costly help (β = 0.48, t = 2.64, p =.014). Co-residence duration explains 37% of the variance on costly in half-siblings (β = 0.44, t = 3.14, p =.003) Co-residence is an input cue to the kin-recognition mechanism Edison Tan Evolutionary Psychology Singapore Management University  The Kinship Premium Other studies have similar findings, using other potentially relevant psychological mediators. Kruger (2003) found no difference in emphatic concern towards siblings or close friends. However, people generally expect to help kin over non-kin and feel that their self-concept (oneness) is more in line with their friends than their siblings. Post-hoc analysis suggest that participants liked, r(444) = 0.36, p <.01, and felt more similar, r(444) = 0.21, p <.01, to their friends than their siblings Only expectancy mediates the relationship between kinship and costly helping intention. Edison Tan Evolutionary Psychology Singapore Management University The Kinship Stewart-William (2007, 2008) When the cost of helping is low (e.g., help with everyday Premium and the tasks), friends receive as much or more help than kin. Helping acquaintances require reciprocation When the cost is high (i.e., one that requires self-sacrifice), Cost of Help people are more likely to help kin. Reciprocation is impossible after altruist self-sacrifice Edison Tan Evolutionary Psychology Singapore Management University  Putting it all together In Curry et al. (2013) genetic relatedness has a unique contribution to altruism above and beyond emotional closeness. In Bressan et al. (2009), full siblings and half-siblings with whom participants had cohabited were helped in life or death most willingly; half-siblings with whom participants had never cohabited and step-siblings were helped least willingly. These preferences were independent of the degree of emotional closeness between siblings. Co-residence during development is a more reliable input to the kin-recognition mechanism than emotional closeness in indicating genetic relatedness. These findings cannot be explained by the tendency to empathize with kins more than with friends – Kruger (2003) found no differences in empathy towards friends or siblings. Findings from Stewart-William (2007, 2008) suggest that while we help close friends more than kin during everyday helping, we are more likely to sacrifice ourselves for kin than for close friends. We expect to help and will help genetic relatives over close friends, particularly for costly help. This is because reciprocal altruism – the basis of help between friends – is not possible in costly help. Altruists cannot enjoy altruistic returns after death. In contrast, costly help can benefit altruists via inclusive fitness enhancement. Edison Tan Evolutionary Psychology Singapore Management University NEXT WEEK: Mid-Terms Examination All the best! 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