Moritz8Notes-1 - Biology1BEvolu tionLecture8(...

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Biology 1B – Evolution Lecture 8 (March 12, 2010) – altruism, speciation Moritz Lecture 8 Notes – page 1 1 Altruism How can we explain the evolution of altruism , or behavior that promotes an individual to make sacrifices to help others? For example, if a bird sees a predator and gives an alarm call to alert other birds to the danger, that action makes the bird more visible to the predator and increases the chance the predator will target it. Altruism will be favored if it increases the fitness of close relatives who share your genes by descent. However, the degree of altruism varies with the degree of relatedness: consider full siblings and first cousins. A full sibling shares 50% of your genes (relatedness factor r = 0.5) A first cousin shares 12.5% of your genes (relatedness factor r = 0.125) Therefore: “I would not lay down my life for a brother, but would do so for 2 brothers or 8 cousins” (Haldane). Haldane says this as a way to show how relatedness affects how many genes would be passing. For example, 2 brothers* ½ relatedness = 1. However, 8 first cousins * 0.125 relatedness = 1. This concept was further formalized into Kin-Selection Theory , which explains when altruism will be beneficial in a reproductive sense. Altruism will be favored if r*B > C, where r is relatedness, B is benefit to the recipient of altruism, and C is the cost to you. For example, consider ground squirrels. They give alarm calls when predators are near: however, it turns out the female squirrels are the only gender to give an alarm call. Further, females reside in the same territory from infanthood to adulthood, while males disperse. Therefore, all the females in one area will be related, and by giving alarm calls that female is
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This note was uploaded on 09/06/2010 for the course CHEM 10894 taught by Professor Pederson during the Fall '10 term at Berkeley.

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Moritz8Notes-1 - Biology1BEvolu tionLecture8(...

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