Levels of Selection

Levels of Selection - Levels of Selection Second important...

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Levels of Selection Second important clarification of adaptation concept has to do with what is called "levels of selection problem" Key issue here is, What level of biological organization (gene, cell, organ, individual, group, population, species, ecosystem, biosphere. ..) are adaptations generally designed to benefit? Darwin had no workable mechanism of inheritance, but the discovery of genes as the primary mechanism of inheritance in organic evolution had many profound consequences for evolutionary theory, including a clarification of the levels of selection issue In particular, linkage of natural selection theory to Mendelian inheritance provided answer to query "survival of the fittest what ?" The ultimate answer is, the fittest gene or gene combination; but of course genes express their fitness (i.e., relative rates of replication) thru their phenotypic effects But what kind of phenotypic effects will be favored by natural selection? In past, biologists often spoke of evolved traits as serving "the good of the species," or even the stability of ecosystems; but there is no basis in evol. biology for supposing that natural selection favors any trait for that reason That's because selection acts via differential fitness of heritable variants, and this process works much more rapidly and effectively on variants that affect individual survival and reproduction than those that affect populations, species, or higher-level categories Thus, in most cases individual-level selection outpaces any higher-level selection To see why, consider example of population regulation discussed by Irons (pp 11-12) If population increases beyond the sustainable limits, it will overharvest its food, and perhaps crash to low levels or even go extinct So wouldn't natural selection favor populations that limit size to sustainable level? Well, population growth is function of individual reproduction; so this really means
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Levels of Selection - Levels of Selection Second important...

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