Bio PPT 12 - The Evolution of Altruism & Cooperation...

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The Evolution of Text © Kurland, 2005
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The Conundrum of Altruism How can reproductively self-sacrificing behavior evolve by natural selection?
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Some Possible Answers Group Selection: group benefit Kin Selection: kin-biased altruism Reciprocity: pay-back altruism
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Dyadic Social Interactions Transaction Actor Recipient Selfishness + Cooperation + + Altruism + Spite + = increase in fitness, Benefit = decrease in fitness, Cost
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Group Selection Indiscriminate altruism benefits the group Altruists incur Fitness-Cost … not Non-Altruists “Altruism allele” decreases each generation
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Kin Selection (W.D.Hamilton,1936-2000) B = Benefit to recipient (+ fitness) C = Cost incurred by actor ( − fitness) r = Relatedness = probability that two individuals share a gene due to descent from a common ancestor
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Hamilton’s Rule for Adaptive Altruism Altruism allele will increase iff Benefit outweighs the Cost: rB > C EX: r = ½ between full-siblings ½ B > C B > 2C
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Bio PPT 12 - The Evolution of Altruism & Cooperation...

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