Anthro 7 Practice MT 4 - Midterm Exam Key Anthro 7 Winter...

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Midterm Exam Key, Anthro 7, Winter 2008 (1) (9 points) Briefly describe three rules of thumb that evolutionary biologists use to decide whether a character is ancestral or derived . Ancestral traits tend to appear earlier in individual development than derived traits. Traits that appear earlier in the fossil record are more likely to be ancestral. Traits of outgroups (a group of organisms outside the group within which the phylogenetic analysis is being done) are likely to be ancestral. (2) Part A. (6 points) According to Darwin’s theory, what three conditions must occur in order for natural selection to occur? Describe each condition in a phrase or a complete sentence, not a single word. More offspring are produced than can survive. Organisms within populations vary, and this variation affects their ability to survive and reproduce. Variation is heritable, i.e. offspring tend to resemble their parents. Part B. (10 points) Use what you wrote in Part A to explain why group selection is usually too weak to produce traits that benefit a group or population but are disadvantageous to the individuals that have these traits. For selection to act on groups, the above three conditions must hold for groups. Variation between groups is reduced by migration between groups. In most animal populations, there is enough migration between groups to keep between- group variation low. This means that, when a trait is disadvantageous to individuals but benefits the groups to which they belong, selection against the trait will probably be much stronger than selection for the trait. (3) (11 points) You tell your roommate that complex adaptations, such as the eye, have evolved gradually from simpler traits. Your roommate says “How can that be, when an eye won’t work at all unless every part is complete? Of what use is 5% of an eye? And how could a complex eye evolve from a very simple eye?
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