Bio+120+Natural+selection%2C+sexual+selection%2C+and+adaptation+Pt-2.+1+CT

Bio+120+Natural+selection%2C+sexual+selection%2C+and+adaptation+Pt-2.+1+CT

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Natural selection, sexual  selection, and adaptation  Evolution in Action
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Evolution:  a definition Some heritable traits help an individual to survive or reproduce better than other individuals. These are the traits that will, over time, increase in frequency in the population, causing evolution the genetically based change in a population's traits over time.
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Natural Selection A population experiences natural selection whenever the following four conditions apply: individuals vary in their traits some of these variations are heritable some individuals survive and reproduce better than other individuals differential survival and reproduction ( fitness ) is influenced by the heritable traits of individuals
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Adaptation An adaptation is a heritable trait that increases an individual's fitness in a particular environment relative to individuals lacking that trait. This concept assumes that the ancestors of the bearers of the trait had the trait and it was advantageous to them. Not all traits are adaptive, and even structures that currently function in organisms may be subject to genetic or historical constraints. We must be attentive to claims that particular traits are adaptations and we will turn to this when we discuss human sexual behavior.
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Constraints on Evolution When selection on alleles for one trait causes a correlated but suboptimal change in another trait, the possible evolutionary outcomes are limited. This type of constraint is called genetic correlation. Lack of genetic variation can also constrain evolution, because natural selection can work only on existing variation in a population. Because all traits evolve from previously existing traits, adaptations are constrained by history. This is called historical constraint. For example, why haven’t we evolved wheels?
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Directional selection Directional selection
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This note was uploaded on 02/17/2011 for the course BIOLOGY 120 taught by Professor Fink during the Winter '11 term at University of Michigan.

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Bio+120+Natural+selection%2C+sexual+selection%2C+and+adaptation+Pt-2.+1+CT

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