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Types of natural selection
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Natural Selection. Natural selection simply refers to differences in survivorship and reproduction among individuals with different phenotypes in a population where reproductive success is correlated with phenotype. Natural selection then is analogous to the artifcial selection practiced by animal and plant breeders in which the breeder selects those organisms which have desired characteristics and breeds those individuals in an attempt to produce off spring who also have the same characteristics. In natural selection, the environment itself is the agent of selection rather than a person intentionally choosing the organisms to be bred. Natural selection is believed to be the mechanism by which adaptations, features of the organism which enhance survival in a particular environment, develop. An adaptation may be a new enzyme varient which functions better at the temperature of the environment or it may be a physical feature of the organism such as color or hair texture which makes the organism less able to be found by a predator or it might be a change in beak size which gives birds with that size beak a competitive edge in gathering food. Some key points: Natural selection need not lead to rapid (if any) evolution, unless the aspect of the phenotype being selected for has a genetic component. It's not always true that the strong survive. A butterfly with white wings living in a dark environment is more likely to be picked off by a predator than a butterfly with wings matching the back ground. Natural selection does not necessarily have any direction, but will track the environment. For example in a population of birds, the smaller birds might be at a disadvantage in a particularly cold winter since they do not have good fat reserves and have more surface area relative to their volume than do larger birds. But in a mild winter with lots of available food, the smaller birds might be an advantage if they are able to hide better from predators or nest in areas the bigger birds can't.
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