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Why do genetic studies support an African origin for Homo sapiens?

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Illustration showing side-by-side reconstructions of five hominins in the human lineage: Australopithecus afarensis, Homo habilis, Homo erectus, Homo neanderthalensis, and Homo sapiens, with each figure labeled and depicted in a walking pose to highlight evolutionary changes in posture and body structure. A scale bar at the top right indicates relative height. — human evolution An artist's depiction of five species of the human lineage.

Genetic studies, particularly those analyzing mitochondrial DNA (mtDNA) and the Y chromosome, provide compelling evidence for an African origin of Homo sapiens through the following key findings:

Greater Genetic Diversity: African populations exhibit significantly higher levels of variability in their mtDNA compared to populations on other continents. This suggests that African populations have been diversifying for a longer period, indicating that the species originated there.1
Nested Lineages: Genetic data show that the mtDNA lineages found in native populations outside of Africa are subsets of the broader, more diverse lineages present in Africa. Specifically, the L3 lineage appears to be the founder from which Asian and European groupings derived.21
Common Ancestry: Comparisons of genetic markers across global populations point to a common descent from a small ancestral population that existed approximately 150,000 years ago, consistent with the "out of Africa" model of human emergence.1

These molecular insights, which align with the fossil record, support the theory that modern humans evolved as an anatomically distinctive species in Africa before migrating to populate the rest of the world.31