Genetic drift

Genetic drift is a contributing factor in biological evolution, in which traits which do not affect reproductive fitness change in a population over time. Whereas natural selection causes traits to become more prevalent when they contribute to fitness, or eliminates those which harm it, genetic drift is a somewhat random process which affects traits that are more neutral.

Genetic drift in populations

Drift can have profound and often bizarre effects on the evolutionary history of a population. These effects may be at odds with the survival of the population.

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In a population bottleneck, where the population suddenly contracts to a small size and then grows again to a large population (believed to have occurred in the history of human evolution), genetic drift can result in sudden and dramatic changes in allele frequency that occur independently of selection. In such instances, many beneficial adaptations may be eliminated.

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Similarly, migrating populations may see founder's effect, where a few individuals with a rare allele in the originating generation can produce a population that has allele frequencies that seem to be at odds with natural selection. Founder's effects are sometimes held to be responsible for high frequencies of some genetic diseases.

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