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Chapter 17

BIOLOGY 1M03 Chapter 17: Chapter 17 - Human Mate Choice and Parenting

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Ben Evans

1 Chapter 17: Human Mate Choice and Parenting The Psychology of Human Mate Preferences  Evolutionary theory generates some testable predictions about the psychology of human mate preferences o For much of evolutionary history, humans have lived in foraging societies o The adaptive challenges that men and women face in these kinds of societies are likely to have shaped their mating strategies o For women, this might have meant choosing men who would provide them with access to resources o It might be important for women to choose a mate who will be a good provider o Men’s reproductive success depends largely on the fertility of their partners so it is plausible that selection favoured men who focused on this attribute o Women’s fertility is highest when they are in their 20s and declines to zero when women reach menopause o Thus, selection should have favoured men who chose young and healthy mates o For both genders, it is important to find mates that they can get along with  If evolution has shaped the psychology of human mating strategies, then we would expect to find common patterns across societies  People generally care most about the personal qualities of their mates o Men and women around the world rate mutual attraction or love above all other traits o The next most highly desirable traits for both are personal attributes, such as dependability, emotional stability and maturity and a pleasing disposition o Interesting and surprising that neither sex seems to value chastity highly o Perhaps because people were asked to evaluate the desirability of sexual experience before marriage, not fidelity during marriage  Men and women show the differences in mate preferences predicted by parental investment theory o Consistent differences between men and women in how desirable each gender thinks traits are o As evolutionary model predicts, women value good financial prospects and ambition more than men do and men value good looks more than women do o No populations in which women value chastity significantly more than men do  Men and women differ about the preferred ages of their partners o Evolutionary reasoning suggests that men’s mate preferences will be strongly influenced by reproductive potential of prospective mates o Thus, we predict that men would choose mates with high fertility or high reproductive value o A considerable amount of evidence suggests that men consistently seek and marry partners who are younger than they are and that women seek and marry partners somewhat older than themselves 2 o As men get older, the age difference between them and their wives increases o As women get older, there is little change in the age difference between them and their husbands  Men and women vary about the preferred number of partners o Women are likely to prefer stable, committed relationships with men who are willing and able to help care for them and their offspring o Men can afford to be more flexible in their mating tactics, which makes them more open to mating opportunities that do not involve long-term commitments  Differences in mating tactics may contribute to misunderstandings between men and women o Some uncertainty arises because you don’t know what the other person’s intentions are o This uncertainty generates different kinds of problems for men and women o A false positive arises if you think that the other person is attracted to you, when in fact they aren’t o A false negative occurs if you think the other person doesn’t like you, when they really do o Both kinds of errors are costly ▪ A false positive could lead you to make an overture that would be rejected ▪ A false negative could prevent you from making any overture at all o Pregnant women are expected to be cautious about their partner’s intentions and as a result, will make more false negative errors than false positive errors ▪ Evolutionary reasoning predicts that women are more likely to underestimate men’s commitment than to overestimate it o Men, who are interested in pursuing both short-term and long-term relationships, are expected to minimize the chance of missing sexual opportunities and as a result will make more false positive errors than false negative errors ▪ They are likely to overestimate women’s sexual interest more often than underestimate it  Culture predicts people’s mate preferences better than gender does o Results showed that country of residence has a greater effect than gender does on variation in all 18 traits o This means that knowing where a person lives tells you more about what he or she values in a mate than knowing the person’s gender does o Ex. Chastity is considered essential in China, but not in Sweden o Data suggests that human mate preferences are strongly influenced by the cultural and economic environment in which they live  Evolutionary analyses of mate choice have generated considerable controversy over at least two different issues o Many people have complained that evolutionary analyses simply reflect and reinforce Western cultural values 3 o Others have questioned the methods used to assess mate preferences and mating tactics o Results derived from “forced choice” tests, in which subjects are asked which of the two alternatives they would choose, sometimes deviate from results in which subjects are asked to rate the same alternatives o This problem arises in studies of sex differences in jealousy o Men will be more upset about their partner’s sexual infidelity than about their emotional infidelity (concerned about being cuckolded) o Women will be more upset about their partner’s emotional infidelity than about their sexual infidelity (concerned about access to resources for themselves and offspring) o Results support this when there are only those two choices o But when both are asked how much they focused on each type of infidelity, sex differences disappeared o One researcher suggests that the forced-choice paradigm provides a misleading picture of sex differences underlying jealousy o It’s possible that men find sexual infidelity more upsetting than emotional infidelity in the forced-choice paradigm because they assume that their partners would not sleep with someone else unless they were emotionally involved with them ▪ Thus, sexual infidelity is more upsetting because it implies both emotional and sexual betrayal o Women may be more upset by emotional infidelity because they assume that if their partners are more emotionally involved with someone else, they are also sleeping with them, but not vice versa Some Social Consequences of Mate Preferences  Kipsigis Bridewealth o Evolutionary theory explains marriage patterns among the Kipsigis, a group of East African pastoralists ▪ Women usually marry in late teens and men usually marry for first time in early 20s ▪ Common for men to have several wives (polygyny) ▪ Groom’s father makes a bridewealth payment to father of bride at time of marriage ▪ The payment compensates for loss of bride’s labour and gives the groom rights to her labour and the children she bears during marriage ▪ Often the bride’s father entertains several competing marriage offers before he chooses a groom for his daughter ▪ Groom’s father is likely to prefer a bride who will bear his son many healthy children ▪ His bridewealth offer is expected to reflect the potential reproductive value of the prospective bride 4 ▪ The groom’s father is also expected to prefer that his son marry a woman who will devote her labour to his household ▪ Kipsigis woman who remain near their own family’s household are likely to be called on to help their mothers with harvest and childbirth ▪ Thus, groom’s father may prefer a women whose natal family is distant from his son’s household ▪ Bride’s father would prefer that his daughter marry a wealthy man and one who lives nearby ▪ Fathers of bride and groom are expected to weigh the costs and benefits of prospective unions in their negotiations over bridewealth payments o Plump women whose menarche occurred at an early age fetched the highest bridewealth payments ▪ Menarche is her first menstruation ▪ Among Kipsigis, age at menarche is a reliable index of women’s reproductive potential ▪ Kipsigis women who reach menarche early have longer reproductive life spans, higher annual fertility and higher survivorship among their offspring than do women who mature at later ages ▪ One way to be sure of a woman’s ability to produce children would be to select one who had already demonstrated her fertility by becoming pregnant ▪ However, bridewealths for such women were typically lower than bridewealths for women who had never conceived ▪ Instead, bridewealth payments were associated with physical attributes of women ▪ Fathers of brides who were considered plump received higher bridewealth payments ▪ Plumpness of prospective brides may be a reliable correlate of age at menarche since menarcheal age is determined partly by body weight ▪ Plumpness may also be valued because a woman’s ability to conceive is determined partly by her nutritional status  Nyinba Polyandry o Polyandry is rare in humans and other mammals ▪ Polyandry is a mating system in which one female is paired with two or more males ▪ Rare because males that share access to a single female produce fewer offspring than do males that maintain exclusive access to one or more females ▪ Reproductive costs may be somewhat reduced if brothers share access to a female, called fraternal polyandry o Polyandrous marriage occurs in several societies in the Himalayas o Evolutionary theory helps explain why some polyandrous marriage are successful and others fail 5 ▪ The more men who are married to a single woman, the lower each man’s reproductive success is likely to be ▪ We might expect marriages with many cohusbands to be less stable than marriages with fewer cohusbands ▪ Results support this ▪ Some Nyinba marriages are arranged by parents, others are set up by the oldest brother ▪ In either case, the wife is usually a few years younger than the oldest cohusband ▪ In some marriages, the youngest cohusbands are considerably younger than their wives ▪ This we might expect that men would be dissatisfied with marriages to women much older than themselves ▪ Men’s decisions to terminate their marriages are associated with their reproductive performance • Men who remained in stable polyandrous marriages fathered an average of 0.1 children per year • Men who terminated their marriages had produced on average only 0.04 children per year during their relationships ▪ Finally, kin selection theory predicts that close kinship among cohusbands would help stabilize polyandrous marriages because men should be more willing to invest in brother’s children ▪ But contrary to predictions, there is no difference in the degree of relatedness among cohusbands in households that remained intact and households that dissolved o Evolutionary theory explains certain aspects of polyandry, but not others Raising Children  In most human societies, parents take on the responsibility of raising their children  Why do people not buy and sell babies like domesticated animals o Many advantages  It seems likely that people do this because their evolved psychology causes them to value their own children very differently from other people’s children  Parenting Effort and Mating Effort o Some human paternal investment is parenting effort, but some is mating effort ▪ Lengthy period of parental investment means that some marriages will end before children are grown ▪ Theory of kin selection generally predicts that men and women will direct care selectively to kin and this might lead them to favour genetic offspring over stepchildren ▪ At the same time, if men and women value their mates’ investment in their children, then care for children might also be a form of mating effort 6 ▪ Results from experiments show that investment in stepchildren reflects mating effort, but not parenting effort ▪ On the other hand, investment in one’s own offspring from a previous marriage reflects parenting effort, but not mating effort ▪ Investment in a mate’s stepchildren from a previous relationship does not constitute parenting effort or mating effort ▪ Anoth
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