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Variations on natural selection

Variations on natural selection. Explaining altruism. I win I lose. How can altruistic behaviors evolve?. you win. cooperation. altruism. Natural selection acts on individuals therefore indv.altruists must benefit. you lose. selfishness. spitefulness.

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Variations on natural selection

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  1. Variations on natural selection Explaining altruism I win I lose How can altruistic behaviors evolve? you win cooperation altruism Natural selection acts on individuals therefore indv.altruists must benefit you lose selfishness spitefulness How can altruism benefit the altruistic individual? Two possible explanations: Kin selection – natural selection based on fitness of relatives Reciprocal altruism – altruistic acts are repaid

  2. Variations on natural selection Kin selection – natural selection based on fitness of relatives direct fitness indirect fitness inclusive fitness + = individual’s own RS benefits through improved RS of relatives Mom Dad x x

  3. Variations on natural selection Kin selection – natural selection based on fitness of relatives direct fitness indirect fitness inclusive fitness + = individual’s own RS benefits through improved RS of relatives increase in relative’s RS Mom Dad = x relatedness x = x B r x “benefit to recipient” “coefficient of relatedness” r= 0.5 r = 0.5

  4. Variations on natural selection Kin selection – natural selection based on fitness of relatives Example: A young bird can either help his parents raise his younger sibs or attempt to breed on his own. With his help, his parents can raise 2 additional young. What is the benefit to the young bird? Should this behavior evolve? indirect fitness benefit =Bxr = 2 x 0.5 = 1 Mom Dad x x What are the costs? direct fitness cost=C = 1 x 0.5 = 0.5 r= 0.5 r = 0.5

  5. Variations on natural selection Kin selection – natural selection based on fitness of relatives Hamilton’s rule: IFB x r–C> 0 THEN the altruistic behavior can evolve indirect fitness gained direct fitness lost because there is a net gain in inclusive fitness B x r>C helping increases inclusive fitness B x r<C helping decreases inclusive fitness direct fitness indirect fitness inclusive fitness + = individual’s own RS benefits through improved RS of relatives

  6. Variations on natural selection Explaining altruism I win I lose How can altruistic behaviors evolve? you win cooperation altruism Natural selection acts on individuals therefore indv.altruists must benefit you lose selfishness spitefulness How can altruism benefit the altruistic individual? Two possible explanations: Kin selection – natural selection based on fitness of relatives Reciprocal altruism – altruistic acts are repaid

  7. Variations on natural selection Reciprocal altruism – altruistic acts are repaid Can helpful behaviors among non-kin evolve? Is the benefit of getting help in the future ≥ the cost of helping? What is the probability of getting help in the future? • Reciprocal altruism is possible when: • Altruism is symmetrical (benefit ≥ cost) • Many opportunities for helping • Individuals interact repeatedly • Individuals have good memories • Cheaters can be punished high probability of getting help

  8. Variations on natural selection Explaining altruism I win I lose How can altruistic behaviors evolve? you win cooperation altruism Natural selection acts on individuals therefore indv.altruists must benefit you lose selfishness spitefulness How can altruism benefit the altruistic individual? Two possible explanations: Kin selection – natural selection based on fitness of relatives Reciprocal altruism – altruistic acts are repaid OR: the apparent altruism may actually help the “altruist”  cooperation

  9. Variations on natural selection Parent-offspring conflict applying Hamilton’s rule to parent-offspring interactions But each kid is more related to itself (r=1.0) than to its sibs (r=0.5) Kids Mom Mom is equally related to all her kids (r = 0.5) Dad

  10. Variations on natural selection Parent-offspring conflict applying Hamilton’s rule to parent-offspring interactions Example: A young bird can continue begging for food from her parents, or she can quit begging, allowing more food for her younger siblings. When should the young bird stop begging? When should the parents cut her off? B = one kid’s survival x 0.5 C = other kid’s survival x 0.5 Benefit = my survival x 1 Cost = sib’s survival x 0.5 Kids Mom As kids gets older, B decreases B Dad age

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