BIO 126 Lecture Notes - Lecture 21: Herbivore, Directional Selection, Crystallin

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Individuals vary within a population with respect to a particular character. There is nonrandom survival and reproduction of variants: result = population evolves. Microevolution: changes with in a species: processes occurring here give rise to macroevolution (new species, change between species) Selection acts only on existing traits, but new traits can evolve through multiple (small) steps. Traits cannot evolve by natural selection unless they increase the individual"s reproductive output. Survival of the fittest : survival + reproduction. Natural selection is non-random, but is not perfect or progressive. Trade-off between speed and resistance level of snake. Directional selection: one trait is favored to either extreme. As seen in previous example, higher toxicity of the newt is favored, so only those with the highest toxicity survive: next generation will become even more toxic, and so on. Favors either extreme, but not the middle or a mix of two traits. Found in environments that are patchy (more than one environment mixed together)

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