Genetic drift is defined as a random change in allele frequencies within a population over time. This phenomenon occurs due to chance events that lead to the disproportionate survival or reproduction of certain genotypes, which can cause specific alleles to become more or less common independently of their influence on fitness.
In smaller populations, genetic drift can have a more pronounced effect because random events can significantly impact the genetic makeup from one generation to the next. For instance, if a natural disaster occurs, it might randomly eliminate a large number of individuals from the population, which could lead to certain alleles being lost entirely while others may become fixed simply due to the influence of chance rather than any selection for or against them.
This randomness is the key characteristic that distinguishes genetic drift from other mechanisms of evolution, such as natural selection which acts on phenotypes rather than directly influencing allele frequencies through chance alone.