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Chapter 17

Chapter 17 How Humans Evolved - Bio 1M03.docx

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McMaster University
James S Quinn

How Humans Evolved Part 4: Evolution And Modern Humans Chapter 17: Human Mate Choice and Parenting The Psychology of Human Mate Preference  Evolutionary theory generates some testable predictions about the psychology of human mate preferences o Humans lived in foraging societies for much of evolutionary history – adaptive challenges in these societies likely shaped mating strategies o Women – choose men who could provide them with resources  Recall that women consume more than they produce o Men – choose women who are young and healthy  Reproductive success depends on fertility of partner  Visual cues that predict youth and health – smooth skin, good muscle tone, symmetrical features, shiny hair o Both – value traits that help sustain relationship; compatibility, agreeableness, reliability, tolerance  Parental investment lasts many years  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  Men and women show the differences in mate preferences predicted by parental investment theory  Men and women differ about the preferred ages of their partners o Men seek younger women; more fertile o Women seek older men; able to provide more resources  Men and women vary about the preferred number of partners o Women desire less sexual partners than men  Women have to invest time and energy into having a child  Women prefer stable, committed relationships – if they invest so much into having a child, their partner must be able to provide for her and her offspring  Women would prefer to decrease the risk of having a child  Differences in mating tactics may contribute to misunderstandings between men and women o Errors and misunderstandings are costly  False Positive – when you believe the other person is attracted to you --- could lead you to make an overture that would be rejected  False Negative – if you think the other person doesn’t like you when they do --- could prevent you from making an overture at all o Hypothesis – Natural selection predisposes men and women to bias their judgments about new partners sexual intentions and commitment in different ways  Women are more likely to underestimate men’s commitments – women who could become pregnant are cautious about partners intentions  More false negative errors than false positive  Men are more likely to overestimate women’s sexual interest – men minimize the chance of missing sexual opportunities  More false positive errors than false negative  Culture predicts people’s mate preferences better than gender does o Chastity shows the greatest variability among populations out of 18 traits  Statistics showed more similarity between men and women in the same country, than among same gender from different populations o Evolutionary explanations that invoke an evolved psychology and cultural explanations that are based on the social and cultural milieu are not mutually exclusive  Evolutionary analyses of mate choice have generated considerable controversy over at least two different issues o Critics – evolutionary analyses reflect and reinforce Western cultural values; celebrate women’s youth and beauty, and men’s wealth and power  Researchers are not studying evolved preferences, but rather learning about cultural values and beliefs o Advocates – cross-cultural uniformity of mate preferences and mating tactics reflects evolved psychological predispositions that are modified, but not created by culture o Sex differences in jealousy  Men – more upset about sexual infidelity  Women – more upset about emotional infidelity Some Social Consequences of Mate Preferences Kipsigis Bridewealth  Evolutionary theory explains marriage patterns among the Kipsigis, a group of East African pastoralists o Grooms father makes a bridewealth payment to the father of the bride at the time of marriage  Tendered in livestock and cash – compensates for family’s loss of brides labour and gives groom rights to her and her children’s labour o Polygyny occurs – there is competition for wives o Grooms father  Prefer brides who will bear many healthy children – bridewealth offer reflects the potential reproductive value of the prospective bride  Prefer brides who will devote labour to sons household – prefer woman whose natal family is distant to sons household, because then she won’t focus much of her time on her own family o Brides Father  Prefer groom to be wealthy to provide bride with more resources  Prefer groom who lives nearby so that bride can help with her own family o Bride and Grooms father must negotiate and weigh costs and benefits  Plump women whose menarche (first menstruation) occurred at an early age fetched the highest bridewealth payments o Age of menarche is a reliable index of women’s reproductive potential o Early menarche = longer reproductive life span, higher annual fertility, higher survivorship among offspring o Women who have been pregnant or produced a child – good indicator of fertility o Plumpness was an indicator of health and fertility Nyinba Polyandry  Polyandry is rare in humans and other mammals o Polyandry – mating system in which one female is paired with two or more males o Polygyny is more common  Females are usually limiting resources for males; males compete for access to females  Males who share a female produce fewer offspring than males that maintain exclusive access to one or more females o Fraternal Polyandry – brothers share access to a female; reduce reproductive cost of polyandry  Male is more likely to care for his brothers offspring than for children unrelated to him (Hamilton’s Rule)  Polyandrous marriage occurs in several societies in the Himalayas o Three brothers married to one female – Nyinba consider this ideal o All brothers marry one female, regardless of the number  Evolutionary theory helps explain why some polyandrous marriages are successful and other fail o The more men married to a single woman, the lower the mans reproductive success  More men = more likely for partition o In Nyinba – wife is a few years younger than oldest son; sometimes youngest cohusband is younger than wife  Men like younger women – younger men tend to initiate partition o Order of reproduction – oldest son has first child, second son has second child etc.  Reproductive success depends on birth order – oldest brother has more children than youngest brother o Kin Selection Theory does not predict accurately in this case  No difference in degree of relatedness among cohusbands that remained intact and households that dissolved  Evolutionary theory explains certain aspects of polyandry but not others o Men leave marriages  Women are older  When they have not fathered many children  Ignoring kinship Raising Children Parenting Effort and Mating Effort  Some human paternal investment is parenting effort, but some is mating effort o The Theory of Kin Selection – predicts that men and women will direct care selectively to kin; they might favour genetic offspring over step children o If men and women value their mates investment in their children – caring for their children might be a form of mating effort o Caring for child from own previous marriage – parenting effort, not mating effort o Hadza, foraging group in Tanzania – mating and parenting effort tradeoff  Marriages are relatively impermanent – men live with women and her children from previous marriages  Men bring home food – men who live with biological children bring a substantially larger amount of food than men who live with at least 1 stepchild  Men spend 2-5% of day caring directly for children  When mating opportunities are limited more time is spent on caring for children – mating parenting tradeoff
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