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How do gene frequencies vary among human populations?

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Overhead view of a diverse group of people standing in a circle, holding each other's hands in a gesture of unity and teamwork. — Race Skin color is one of the variables that has been used to classify people into different racial categories.

In the context of human biology, it is important to clarify that the concept of biological "race" as a division of humanity into distinct subspecies is scientifically invalid. Human populations do not fall into neat, bounded racial categories; rather, genetic differences are expressed in subtle gradations across geographic space, and internal variation within any given population is often greater than the variation between different populations.12

Gene frequencies vary among human populations due to several evolutionary processes:

Genetic Drift: This is a change in gene frequency caused by pure chance, which has a more pronounced effect in small populations. The founder principle occurs when a new population is established by a few individuals, whose specific allele frequencies may differ significantly from the parent population. Similarly, population bottlenecks—drastic reductions in population size due to disease or disaster—can permanently alter the genetic composition of a group.345
Natural Selection: Environmental pressures drive variations in gene frequency. For example, populations in equatorial regions were historically under selective pressure favoring darker skin to protect against sun exposure, while populations in polar latitudes experienced pressure favoring lighter skin to facilitate vitamin D synthesis.5
Gene Flow: The migration of individuals and subsequent interbreeding between populations introduces new alleles into a gene pool, altering the frequency of existing genes.6

Ultimately, while scientists use genetic markers to track human migration and ancestry, these data demonstrate that all humans share a common ancestry and that no genetic evidence supports the existence of biological races.251