Chapter 7 Altruism, Kin Selection, and Parenting

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

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

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

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

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

Risk Relative Risk of Homocide Spouses Other Nonrelative OffspringParent Other relatives

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

Henry II and Eleanor of Aquitane King of England 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

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

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

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

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

Lions 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

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

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

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

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

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

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

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

Having Multiple Offspring Insurance hypothesis Opportunism hypothesis –Resource dependent

Infanticide Non-normative behaviour Cross-cultural Last resort

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

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

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

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

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

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?

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

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

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

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

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)

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

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

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