Lecture VII - Social Evolution and Kin Selection

Lecture VII - Social Evolution and Kin Selection -...

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LectureVII – Social Evolution and Kin Selection
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Individuals and Groups Natural selection occurs on the individual, i.e., every individual attempts to optimize its own fitness Nonetheless, many animal species, especially social species, seem to act altruistically, that is they help other individuals at their own expense http://www.chimpanzoo.org/pics/african_notecards/soc.jpg
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Individuals and Groups Even when they don’t actively assist other individuals, most individual animals do not interact aggressively, even when foraging for resources Different rules seem to determine interactions between individuals of a species http://pictopia.com/perl/get_image?provider_id=318&size=550x550_mb&ptp_photo_id=283080
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Social Animals and Altruism The first explanation for altruism was “group selection” The idea behind this is that cooperative groups have higher success than groups comprised of selfish individuals This idea has some theoretical background Furthermore, it appeals to a certain moral sense of it’s supporters
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Group Selection The main supporter of this idea, M. J. Wade, sees this type of mechanism working in cases where the unit of selection is the group This may occur when most populations are established by small groups of individuals and are replaced by another groups spreading and replacing it In this scenario, an altruistic group will be more successful and replace a group comprised of selfish individuals http://www.ento.vt.edu/~sharov/biosem/txt/selfish2.gif
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Group Selection However, the scenario envisioned for group selection rarely, if ever occurs in nature Groups are not, in most cases, the unit of selection: A selfish individual living within a altruistic group will have higher fitness than its altruistic neighbors In very few generations, selfish individuals will have replaced all others
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Group Selection How does this look? Let us say: p = frequency of altruists in the group c = cost of altruism, or the reduction in individual fitness of altruist to help others b = benefit to the group due to altruistic behavior • w A = Fitness of an Altruist • w S = Fitness of a Selfish individual http://biology.mcgill.ca/faculty/hendry/shallow.jpg
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Group Selection So, assuming that b > c for each individual Fitness of a population of altruists: w A = (1+ ( p ×( b c ))/ n ) × n Individual fitness for each member of this population:
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Lecture VII - Social Evolution and Kin Selection -...

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