Learn & Understand

Reading Migrations in the Genome: Genetic Distance

Populations that have been separated for a long time drift apart genetically, accumulating differences in how common each gene variant is. Measuring this “genetic distance” lets scientists reconstruct the deep history of populations — including the great human journey out of Africa that peopled the world.

Populations Drift Apart

When groups of a species become separated, their gene pools begin to diverge. Chance, different selection pressures, and lack of interbreeding cause the frequency of gene variants to shift independently in each group. Over time, the populations grow genetically distinct — and the degree of that distinctness, the genetic distance, records how long and how completely they have been apart.

Measuring the Divergence

Genetic distance quantifies how different two populations' allele frequencies are, condensing many small differences into a single figure. A distance near zero means the populations are genetically almost identical; larger values mean greater divergence. Averaged across many genes, it gives a robust measure of how related or separated two populations truly are.

The Human Story

Applied to human populations, genetic distance helped reveal a profound story: that modern humans arose in Africa and spread outward across the globe. Populations show greatest genetic diversity in Africa and progressively less the farther one traces the migratory routes away from it — a genetic trail of the journeys by which our species populated every continent.

Trees of Relationship

By computing genetic distances among many populations, researchers build branching trees that depict how populations split and spread over time, much like a family tree at the scale of whole peoples. These reconstructions, drawn from the frequencies of genes, let us read migrations and separations that happened long before any written record — history recovered from the genome itself.

Calculating Distance

To compute genetic distance between two populations, use the Genetic Distance Calculator. Contrast it with individual relatedness via the Genetic Relatedness Calculator, and measure diversity with the Heterozygosity Calculator.