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Natural selection is easy to understand, but it often is misunderstood much too. Natural selection is not synonymous with evolution. Evolution refers to any hereditary change in a people, whereas natural selection specifies a definite way in which such changes are brought about. Natural selection is the most crucial agent of evolutionary change due to the fact it results in adaptation of an organism to its environment.
Other possible mechanisms of progression besides natural selection include gene circulation, meiotic drive, and genetic drift. A persistent misconception is that natural selection occurs mainly through differences between organisms in death rates, or differential mortality. Differential mortality can be selective but only to the degree that it creates distinctions between individuals in the amount of reproductive offspring they produce. Reproductive rate, rather than death rate, drives natural selection. A careful tomcat that rarely crosses busy streets might live to a ripe later years without leaving behind as much descendent kittens as another less staid tomcat wiped out on the highway at a much more youthful age.
If the short-lived cat leaves more descendants, its genes will spread faster than those of the long-lived cat, and natural selection will prefer a short life span. Unless living longer allows or results in higher reproductive success, long life is not favored by natural selection. Adaptations designed by natural selection suit an organism to its particular environment.
For example, a maple tree’s wide leaves are well adapted to temperate climates, but unsuited to arctic chilly. Similarly, a human’s ability to store fat is an version to environments in which body fat is scarce, but is badly suited to the present day fast-food environment. In this respect, natural selection is shortsighted somewhat, since it cannot “see” beyond another generation.
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Natural selection cannot preferentially create favorable variations, but must use what is at hand instead. For instance, treatment with antibiotics does not create antibiotic-resistant mutants. Instead, it favors microbes that, by chance, curently have genes for level of resistance. Phrases such as “the struggle for existence” and “survival of the fittest” have had an unfortunate consequence.
They tend to emphasize predation and fighting for food as the common means of selection. This reinforces erroneous emphasis on differential death rates, with the strongest and fastest individuals being regarded as creating a selective advantage over weaker and slower individuals. But if this were true, every types would constantly gain in power and rate. Because this is not happening, selection against increased strength and speed (counterselection) must be occurring and must limit the procedure.
Natural selection will not operate “for the advantage of the varieties.” Birds lay fewer eggs during drought years. Is this because competition for limited food materials would be detrimental to the types, and do wild birds restrain “for the nice of their types”? Such arguments have a fatal flaw: “cheaters” that laid as much eggs as is possible would reap an increased reproductive success than individuals that voluntarily reduced their clutch size. As time passes, cheater genes would spread through a people, and genes for holding-back would become uncommon. However, the same phenomenon can be interpreted more plausibly in conditions of natural selection at the level of individuals.
During droughts, parental wild birds cannot bring as many insects to their nest and for that reason cannot feed and fledge as much chicks as they can when food items are more adequate. Laying extra eggs means most chicks would perish of starvation. Birds can in fact leave more making it through offspring to breed within the next generation by laying fewer eggs.