Altruism,%20Kin%20Selection,%20and%20Parenting

1
Chapter 7

• Altruism, Kin Selection, and Parenting

2
(Basic) Altruism

• Cost to self for the benefit of another
• Evolutionary interpretation doesnt 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
• Hamiltons rule rbgtc

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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

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

• Mothers and sons
• Ally against father
• Oedipus complex
• Sexual competition between fathers and sons
• Evolutionary interpretation
• Successful polygamist
• Resources
• Mothers interest coincides with sons

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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

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Kin Selection and Kin Conflict

• Doesnt 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

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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

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Adoption

• Violation of kin selection?
• Hamiltons rule
• rB gt C
• Maladaptive, neutral, adaptive?
• Who? When? Why?
• EEA?
• Silks (1990) work on South Pacific society
• Chimpanzee aunts

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Step Parenting

• One biological parent, one non-biological
• Conflict
• Resources, energy, reproduction

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Lions

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

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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

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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

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Human Complexity

• Network of
• Connections
• Obligations
• Step-child and step parent
• Parent and step parent
• Half-siblings

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Trends

• Severity/incidence of child maltreatment
  decreases with age of child
• Disagrees with non-evolutionary theory
• Wide range of abuse types
• Abuse decreases as mothers age increases
• Type of fatal abuse
• Step-parent bludgeoned, kicked, battered
• Genetic parent less assaultive murder-suicide

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Cross Cultural

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

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An Adapted Trait?

• Sexually selected infanticide
• Currently non-adaptive or maladaptive in humans
• Humans arent lions or langurs
• Reciprocity
• Risky
• e.g., child abusers in prison

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Parental Considerations

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

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Having Multiple Offspring

• Insurance hypothesis
• Opportunism hypothesis
• Resource dependent

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Infanticide

• Non-normative behaviour
• Cross-cultural
• Last resort

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Optimization Decisions

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

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Limited Parental Resources

• Abandonment
• Personal parental survival ranked above offspring
  survival
• Live to reproduce another day
• Abortion
• Age dependent

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Foetal Fitness Spontaneous Abortions

• 30-75
• Low quality embryo
• Human chorionic gonadotrophin (hCG)
• Signals embryos fitness --gt progesterone
• Mothers ability
• Environmental constraints
• Genotype

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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

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Sex Ratios

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

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Trivers-Willard Effect

• Slight modification of Fishers principle
• Not equal numbers of each sex
• Preference for children of a particular sex
• Biased sex ratio
• Investment in each sex balanced against the sexs
  reproductive potential
• Which sex is going to be more reproductively
  successful?

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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

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Factors

• In utero differentiation
• Maternal stress --gt 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

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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

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Teen Pregnancy

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

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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)

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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

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Evidence Trinidadian Study

• Only one reproductive female per household
• Daughters only become pregnant after their
  mothers last child is 4 years old
• Mother-daughter conflict
• Greatest if daughter of childbearing age and
  mother still reproducing
• Correlational

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Issues

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