What is genetic drift?

Genetic drift refers to the random changes in allele frequencies within a population from one generation to the next, primarily due to chance events. It is a mechanism of evolution that can lead to significant shifts in genetic variation, particularly in smaller populations where random events can have a more pronounced impact. This unpredictability arises because allele frequencies can increase or decrease not due to selective pressures but rather due to random sampling of the population.

For example, if a natural disaster drastically reduces the size of a population, the surviving members' genetic makeup may not represent the original population's genetic diversity. Over time, certain alleles may become more common or completely lost from the population purely by chance, which demonstrates the essence of genetic drift.

Genetic drift contrasts with methods of natural selection, which are predictable and involve differential survival and reproduction based on advantageous traits. Additionally, it does not systematically increase genetic variation, as it can lead to the loss of alleles and reduce diversity within a population.