EvoPrint - Evolution (Caption Pending) Evolution When...

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(Caption Pending) Evolution
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When evolution is discussed, the user is normally trying to convey the idea of descent with modification . Charles Darwin first used this phrase in his revolutionary book, “The Origin of Species”, which was published in 1859. In “The Origin of Species” Darwin outlined his ideas describing how the earth came to be populated with the diversity of species alive past and present. Descent with modification explains how new species arise from ancestral species by undergoing incremental changes that are inherited and passed onto new generations. Descent with modification also works on a smaller scale and can describe changes in the traits of a population from one generation to the next. The force that determines which changes are beneficial and thus are passed along with a higher frequency is called natural selection . Natural selection is a mechanism of evolution. Natural selection comes into play because the environment of a population of organisms is unable to support all of the offspring that could theoretically be produced by the population. Let's consider a population of black and yellow argiope spiders living in a meadow and estimate that the population consists of approximately 1000 female spiders and 1000 male spiders. Members of this species of spider die after they reproduce leaving their children to repopulate the meadow. There is room for 2000 spiders in the meadow, however a single argiope Evolution
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spider couple produces from 300-1400 offspring. If every female spider produced the maximum amount of offspring she could, there would be 1.4 million spiders running around a meadow that can handle only 2000! Obviously most of the potentially new argiope spiders will not be born at all or will die in the meadow while competing for the scarce resources. If natural selection were not a reality, then the death of each non-surviving spider would be completely random. The abilities and actions of the spiders themselves would have no role in if they or their offspring live or die. While chance does play a role in survival, natural selection also has a great effect. Resources such as energy and shelter are an important consideration when it comes to ensuring the survival of an organism. If an argiope spider is to survive, it must be able to catch food to feed itself. Spiders who build weaker webs might not catch as many insects and could starve to death meaning they will not reproduce while spiders who build strong webs will have a steady food supply and will be able to reproduce. This difference in abilities and others like it means there is variation among spiders though to our undiscriminating eye, all spiders might “look” identical. Another important aspect of survival is avoiding predators.
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This note was uploaded on 04/21/2008 for the course BIOL 100 taught by Professor Lee during the Winter '07 term at San Diego State.

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EvoPrint - Evolution (Caption Pending) Evolution When...

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