Chapter 7

1. Chapter 7 Altruism, Kin Selection, and Parenting

2. (Basic) Altruism • Cost to self for the benefit of another • Evolutionary interpretation doesn’t require intent • Kin selection

3. Fitness • Direct and indirect fitness • Together make inclusive fitness • Coefficient of relatedness, r • Explains issues of kin selection

4. Kin Selection • Selection that operates on an individual in any way that effects the frequency of genes shared by common descent in relatives • Hamilton’s rule: rb>c

5. Proximate or Ultimate • Levels of causation • Altruistic act • Proximate level: altruistic • Consider the individual as the active unit/agent • Donor loses out, but recipient gains • Ultimate level: selfish • Consider the genes as the active units/agents • Donor loses direct fitness, but gains enough indirect fitness to offset loss in long run

6. Domestic Violence • High proportion of murders • Approximately 25% • Conflict with fitness accounts? • Maybe not… • Approximately 4/5 domestic murders are relatives by marriage • Only 1 in 5 are relatives by blood

7. Risk 4 3 2 1 Relative Risk of Homocide Spouses Other Nonrelative Offspring Parent Other relatives

8. Alliances • Mothers and sons • Ally against father • Oedipus complex • Sexual competition between fathers and sons • Evolutionary interpretation • Successful polygamist • Resources • Mother’s interest coincides with son’s

9. Henry II and Eleanor of Aquitane • King of England 1154-1189 • Married 1152 • Eleanor 12 years older • Henry unfaithful • 5 sons, 3 daughters • Richard the Lionhearted, John I • Division of lands • Rebellion in 1173 • Eleanor sides with sons • Imprisoned until 1189

10. Kin Selection and Kin Conflict • Doesn’t predict altruism must occur • Just that altruism is more likely to occur, all else being equal • Costs and benefits • If benefits high enough, kin can be sacrificed • Altruism shifts to selfishness

11. Take Home Message • Biological kinship is important • Discriminate in favour of kin • E.g., Shavit et al. (1994), air raid shelters • E.g., Burnstein et al. (1994), hypothetical life/death situations and the giving of aid • But, favourable kinship discrimination is not inviolable • Kinship is only one factor in behaviour determination • Inclusive vs. direct fitness

12. Adoption • Violation of kin selection? • Hamilton’s rule • rB > C • Maladaptive, neutral, adaptive? • Who? When? Why? • EEA? • Silk’s (1990) work on South Pacific society • Chimpanzee aunts

13. Step Parenting • One biological parent, one non-biological • Conflict • Resources, energy, reproduction

14. Females stay with pride, young males leave Dominant male displaced New male needs to impregnate females quickly Systematic killing of predecessor’s cubs Effects of nursing Reduction in ovulation --> reduced probability of conception Selected for through evolution Lactation stops, ovulation returns to normal --> increases male lion’s direct fitness Similar pattern of behaviour seen in primates (e.g., langurs) and birds Lions

15. Human Condition • Martin Daly and Margo Wilson • Step-children stand an increased risk of maltreatment from their step-parent • Canadian step children • 60 times more likely to suffer fatal abuse by step-parent than children living with genetic parents • Step-parent investment • Sacrifice of reproductive success

16. Resource Limitation • Finite parental resources • Examples • Homeless adolescents in New York • In Britain, genetic and step parent have lower educational aspirations for stepchild • In USA, stepchildren in university receive less financial help from parents

17. Human Complexity • Network of: • Connections • Obligations • Step-child and step parent • Parent and step parent • Half-siblings

18. Trends • Severity/incidence of child maltreatment decreases with age of child • Disagrees with non-evolutionary theory • Wide range of abuse types • Abuse decreases as mother’s age increases • Type of fatal abuse • Step-parent: bludgeoned, kicked, battered • Genetic parent: “less assaultive”; murder-suicide

19. Cross Cultural • USA, Canada, Great Britain, Australia, Finland, Japan, Korea, Nigeria, Hong Kong, Trinidad • Not identical, but similar patterns

20. An Adapted Trait? • Sexually selected infanticide • Currently non-adaptive or maladaptive in humans • Humans aren’t lions or langurs • Reciprocity • Risky • e.g., child abusers in prison

21. Parental Considerations • Present and future survivorship • Future fertility • Personal genetic fitness • Gain from reproduction vs. loss from change in life cycle • Environmental constraints

22. Having Multiple Offspring • Insurance hypothesis • Opportunism hypothesis • Resource dependent

23. Infanticide • Non-normative behaviour • Cross-cultural • Last resort

24. Optimization Decisions • Abandonment of young and/or old • Personal vs. offspring survival • Survive to reproduce another day • RV

25. Limited Parental Resources • Abandonment • Personal parental survival ranked above offspring survival • Live to reproduce another day • Abortion • Age dependent

26. Foetal Fitness: Spontaneous Abortions • 30-75% • Low quality embryo • Human chorionic gonadotrophin (hCG) • Signal’s embryo’s fitness --> progesterone • Mother’s ability • Environmental constraints • Genotype

27. Poor Infant Quality • Physical and/or mental disability • Investment cost vs. genetic pay-off • Disabilities may be relatively minor • Phenotypic signals of genotype • e.g., breech birth correlated with SIDS

28. Sex Ratios • Fisher’s principle • Male births infrequent --> male finds many mates • Parents that produce more males will get more grandchildren • Male-producing gene spreads • Males outnumber females • Now, female births infrenquent --> female can pick mate • Selection favours female-producing genes • Feedback loop ---> 50/50 sex ratio

29. Trivers-Willard Effect • Slight modification of Fisher’s principle • Not equal numbers of each sex • Preference for children of a particular sex • Biased sex ratio • Investment in each sex balanced against the sex’s reproductive potential • Which sex is going to be more reproductively successful?

30. Trivers-Willard Reasoning • Large, healthy males mate more than small males; almost all females mate • Healthiest females produce healthiest offspring, which grow into largest adults • Therefore: • healthy females should produce more males than females • less healthy females should produce more females than males

31. Factors • In utero differentiation • Maternal stress --> higher male fetal mortality • Infanticide • Intentional and unintentional • Adult sex ratio • Sex ratio at birth • Differences in male/female maturation times • Differential male/female mortality

32. Local Resource Enhancement • Offspring of one sex provide greater assistance to parents • Increase parents’ reproductive output • Greater investment in this sex • Helpers-at-the-nest model • Local resource competition

33. Teen Pregnancy • Ignorance or unintended • Deliberate attempt to gain resources • Social security and/or husband • Adaptive reproductive strategy?

34. Female Shared Childrearing • Lower socio-economic women • Poor job and marriage prospects • May improve with age • Have child at about 15 • Over three generations • Mother: age 15 (reproductive) • Grandmother: age 35 (worker) • Great grandmother: age 50 (childcare)

35. Cost/Benefit • Mother sacrifices resource acquisition (RA), gains personal reproductive fitness (PRF) • Grandmother sacrifices PRF, gains inclusive fitness (IF), gains RA • Great grandmother sacrifices RA and PRF, gains IF

36. Evidence: Trinidadian Study • Only one reproductive female per household • Daughters only become pregnant after their mother’s last child is 4+ years old • Mother-daughter conflict • Greatest if daughter of childbearing age and mother still reproducing • Correlational

37. Issues • How is reproduction regulated? • Multi-daughter families? • Historical evidence? • Cross-cultural? • Correlational results • Interesting, but...