Chapter Summary

A basic theory of evolution involves the production of new genetic variation by mutation and the continual mixing of that variation at reproduction. Gene flow and the forms of genetic drift (fission, the founder effect that results from fission, and gamete sampling) act to randomly change allele frequencies within populations of a species. The resulting phenotypic variation becomes the raw material for natural selection that selects individuals for reproductive success, thus accumulating adaptive traits across generations and decreasing the frequency of poorly adapted traits.

The basic unit of evolution is the species, an interbreeding population that is reproductively isolated from other populations. Because the evolution of new species is a process that occurs over time and at differing rates, species are not always equally distinct from one another and can often be difficult to define. Species are characterized genetically by allele frequency, the percentage of times each possible allele of a gene occurs. Evolution is thus technically defined ads a change in allele frequency over time.

The processes of evolution, based on this definition, are:

1. Mutation—mistakes in the genetic mechanism that add new variation to a species’ gene pool.
2. Natural Selection—the differential reproduction of individuals based on the relative adaptive value of their traits.
3. Gene Flow—the mixing of genes as populations within a species move about interbreed.
4. Genetic drift—the splitting of populations to found new populations with new sets of allele frequencies 9fission and the founder effect) and the nonrepresentative sampling of genes as each new generation is produced (gamete sampling).

Sickle cell anemia is not only an example of the processes of evolution at work but is also an example of anthropology’s holistic approach—the search for connections among the various aspects of its subject.

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