How much genetic variation exists within versus between human populations?
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Executive summary
Most human genetic diversity is found within local populations, not between them: classical estimates put roughly 80–95% (commonly cited as ~85%) of variation within populations and only about 5–15% between populations, a result replicated by many modern genomic studies; however, a small fraction of variants and some traits do show geographically structured differences that allow ancestry inference and local adaptation studies [1] [2] [3] [4].
1. The headline numbers and where they come from
Early and continuing population-genetic analyses—starting with Lewontin’s apportionment and summarized in authoritative resources—report that roughly 85% of human genetic variation is found within populations and about 15% between populations, with the broader literature putting the within-population share in the 80–95% range depending on markers and sampling [1] [2] [5].
2. What “within” versus “between” actually means in practice
“Within-population” variation refers to differences among individuals living in the same local group; “between-population” variation denotes average allele-frequency differences across groups or regions, often quantified by fixation indices like FST—human continental groups typically show modest FST values (e.g., ~0.05–0.15 in many studies), indicating more similarity than difference at most loci [6] [7] [2].
3. Modern genomics confirms the pattern but adds nuance
Large-scale whole-genome sequencing of diverse populations finds many previously undocumented common variants that are private to particular regions (especially in Africa and Oceania) yet also finds an absence of variants fixed between major geographical regions, emphasizing continuous clines of variation and deep, gradual separations rather than discrete genetic blocks [4] [8].
4. Why so much variation is inside groups: drift, migration and demography
Population-genetics theory and empirical work attribute the dominance of within-group variation to processes like gene flow (which homogenizes populations), random genetic drift in small groups, and demographic events (bottlenecks and expansions) that shape allele frequencies over time; gene flow in particular decreases inter-population differences while increasing intra-population diversity [9] [10].
5. Limits of the “most variation is within” slogan — classification and important exceptions
Although most variation is within groups, a sufficiently large set of genetic markers can classify individuals to geographic ancestry with high accuracy because the small among-population component is structured and consistent across loci; moreover, traits under strong local selection—skin pigmentation, lactose tolerance, high-altitude adaptations, some drug-response alleles—can show substantial between-population differences relevant to medicine and anthropology [3] [7] [4].
6. Gene expression and phenotype: parallels to DNA-level findings
Work decomposing gene-expression variation echoes DNA results: most expression differences arise among individuals rather than among populations, though population-differentially expressed genes exist and may point to disease susceptibilities or adaptation loci—thus the within-vs-between partition applies across molecular phenotypes, with caveats about tissue, environment and selection [11] [12].
7. Implications for “race” and for research or medicine
The quantitative fact that most genetic diversity is within populations has been used to argue that traditional racial categories lack sharp biological boundaries, a conclusion reinforced by genomic gradients and continuous variation; simultaneously, researchers caution that population structure matters for disease mapping, pharmacogenomics and understanding human history, so social and medical contexts require both the acknowledgement of shared variation and attention to real population-specific patterns [1] [13] [14].