Genetic drift

Genetic drift is the random change in genetic composition of a population across generations, driven by chance rather than Natural selection. Unlike selection, which favors beneficial traits, drift is indifferent—alleles can increase or decrease in frequency purely by accident, especially in small populations.

Imagine a jar of colored marbles representing different gene variants. Each generation, you randomly draw marbles to "reproduce." Sometimes, by sheer luck, you'll draw more of one color, shifting the jar's contents. Draw long enough, and colors vanish entirely—that's drift.

This phenomenon has profound consequences. In small, isolated populations—like island colonists or endangered species—drift can eliminate valuable genetic diversity faster than selection can maintain it. It explains why genetic variation differs among indigenous populations and why some rare alleles persist in small communities despite offering no survival advantage.

Drift also complicates Genetic engineering and conservation efforts: protecting populations requires maintaining size to resist random genetic loss. The process interacts subtly with selection, mutation, and migration, making real evolutionary dynamics messier than textbook simplicity suggests.

Related

Evolution, Population genetics, Allele, Biodiversity, Statistical variation, Mutation