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

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Spouses OtherNonrelative

Offspring Parent Otherrelatives

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

– 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...