Chapter 7 Altruism Kin Selection and Parenting Basic

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

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

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 – r. B > 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 (h. CG) • 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. . .