random drift

The term random drift actually encompasses a number of distinct processes, sometimes referred to as outcomes. They include indiscriminate parent sampling, the founder effect, and fluctuations in the rate of evolutionary processes such as selection, migration, and mutation. Parent sampling is the process of determining which organisms of one generation will be the parents of the next generation. Parent sampling may be discriminate, that is, with regard to fitness differences, or indiscriminate, without regard to fitness differences. Discriminate parent sampling is generally considered natural selection, whereas indiscriminate parent sampling is considered random drift.