Altruism and the Family The Genetical Evolution of Social Behaviour

The Problem of Altruism “The quality of unselfish concern for the welfare of others” Darwin recognised that it posed a problem for evolutionary theory How could it evolve? Group selection vs. selfish genes

Kin Selection Theory Based on Hamiltonian inclusive fitness Hamilton’s rule: c < br  c = cost, in reproductive terms, to focal individual  b = benefit, in reproductive terms, to related individuals  r = degree of genetic relatedness

Some Hypothetical Scenarios You walk by a house one evening to see it on fire. Through the windows, you can see:  A complete stranger  A sibling  Three strangers  Three siblings Whom do you save?

Relations and Relatedness Full sibs:.50 Offspring:.50 Parents:.50 Half-sibs:.25 Grandparents:.25 Nieces/Nephews:.25 First cousins:.125

Universal Nature of Kinship Ego-centred terminology Sex & generation are distinguished  Reproductive problems (e.g., variance, paternity certainty, etc.) & value “Close” relations are typically closely genetically related Generational conflict over degree of altruism

Ground Squirrels Hypotheses: predator confusion, predator deterrence, reciprocal altruism, parental investment, inclusive fitness Risk increases for alarm-caller (nix 1 & 2) Alarm calling not related to length of interaction with surrounding squirrels (nix 3) Females without offspring but with genetic relatives present still sound alarm (nix 4)

Patterns of Inheritance Knowing kin selection theory, what pattern would we predict? Smith, Kish, & Crawford (1987)  1° Kin (r=.50): 46.5% (mostly to offspring)  Spouse: 36.9% (assumed to provide for offspring)  2° Kin (r=.25): 8.3%  3° Kin (r=.125): 0.6%  Nonkin: 7.7%

Grandparental Investment Since grandparents are (typically) past their reproductive prime, we might expect investment in grandchildren Due to paternity uncertainty, though, there should be differences in investment (“discriminative grandparental solicitude”) Grandmother & Patriarch explanations of menopause

The Eusocial Insects (1) The order Hymenoptera  Bees, ants, wasps  Sterile female worker castes  Haplodiploid system of genetic inheritance Unfertilised eggs become male (haploid) Fertilised eggs become females (diploid)

The Eusocial Insects (2) Sisters help mother produce more sisters, which increases inclusive fitness

The Evolution of the Family (1) Emlen (1995)  Families form when More offspring produced than available reproductive vacancies Offspring must wait until they are ready to compete for reproductive vacancies Benefits of remaining together are high (e.g., resources)

Davis & Daly (1997)  Human families are somewhat unique Families give advantages in group-on- group competition Reciprocal altruism Nonreproductive helping The Evolution of the Family (2)

The Wrap-Up Kin altruism: explainable by Hamilton’s rule Examples of nepotistic behaviour Haplodiploidy and the evolution of altruism in the order Hymenoptera The evolution of the family

Things to Come Cooperation  Reciprocal altruism  Game theory  Cheater detection  Friendship