NaturalSelection2010

NaturalSelection2010 - Natural Selection! Galapagos Land...

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Natural Selection Galapagos Land Iguana
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Fact 1 : populations will increase exponentially unless constrained. (evidence = mathematical models & observation) Fact 2 : Size of populations of most organisms tends to remain fairly stable over time. (Evidence = observation) Population size (n)
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Fact 3 : The resources available to each species are limited. (evidence = observation, reinforced by Malthus) Therefore, we can infer that a struggle for existence will occur. Fact 4 : No two individuals within a population are identical due to mutation and recombination (evidence = observation). Therefore, they probably differ in their ability to survive and reproduce, and so some will do better than others (Natural Selection).
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Fact 5 : Many of the differences among individuals are at least in part heritable. (evidence = “like breeds like”) Therefore, natural selection, operating over many generations, results in evolution. Biological evolution is change in the properties of groups of organisms over the course of generations. The changes must be passed via genes from one generation to the next. For example, if large body size is favored over small size, then a population (or species) will come to be dominated by individuals of larger size over time. The mean size will increase. Individuals do not evolve. Populations or species do. Time
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What is a population? A local subset of a species. Also sometimes called a deme and described as a community of potentially interbreeding individuals at a given locality. What is a species? Collection of individuals that interbreed or potentially interbreed with one another - and produce viable, fertile offspring - under natural conditions. Usually species have patchy distributions that follow habitat preferences. Evolution occurs within each population, potentially creating differences among them. Gene Fow (breeding between populations) will counteract the tendency to diverge.
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Time Natural selection is a process of elimination , unlike artiFcial selection in which we choose who breeds. Natural selection is mindless - the “blind watchmaker” in which “design” or “improvements” occur as a result of selective death of some individuals but without a goal and no knowledge of the future. I.E. Natural selection is not goal directed. Natural selection results in “survival of the fittest” but what do we mean by “fittest?” Two aspects of Ftness: 1) survival Ftness : the ability to live long enough to reproduce. 2) reproductive Ftness : the ability to reproduce. The features shared by individuals who have a long lifespan and produce many offspring are likely to dominate future populations. Survival Ftness : Consider the peppered moth - melanistic forms were more likely to survive when the trees were darkened by pollution.
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The quest for high Reproductive Ftness drives SEXUAL SELECTION . Sexual selection is a form of natural
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NaturalSelection2010 - Natural Selection! Galapagos Land...

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