Dozens of scientific papers published since 1981 describe worldwide mtDNA variation. In most continental, national, or regional databases, it is characteristic to observe many rare types with frequencies well below 1% and a few common types with frequencies exceeding 1%. For example, one type is present in about 4% of North Americans. A few other common types have frequencies of less than 3%.

Exceptions to this overall high diversity are Native Americans, African Pygmies, and other groups that tend to be anthropologically interesting because of their geographic isolation. Most have had small population sizes in recent history that limited or reduced their genetic diversity, including their mtDNA variation.

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