Transcript Lecture 2 - Organic Origins Debate

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?
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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
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Some Hypothetical Scenarios
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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
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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)
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Patterns of Inheritance
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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
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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)
Mother Daughter Sister Father Son Brother
Female 0.5
0.5
0.75 0.5 0.5 0.5
Male
1
1
0.5
NA NA 0.5
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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)
The Evolution of the Family (2)

Davis & Daly (1997)
 Human families are somewhat unique
 Families give advantages in group-ongroup competition
 Reciprocal altruism
 Nonreproductive helping
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
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Things to Come
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Cooperation
 Reciprocal altruism
 Game theory
 Cheater detection
 Friendship