The Cambridge Reference Sequence (CRS), the human mitochondrial sequence to which all other sequences are compared, belongs to haplogroup H.
About one half of Europeans are of mt-DNA haplogroup H. The haplogroup is also common in North Africa and the Middle East. The majority of the European populations have an overall haplogroup H frequency of 40%–50%. Frequencies decrease in the southeast of the continent, reaching 20% in the Near East and Caucasus, and <10% in the Persian Gulf, Northern India and Central Asia.
Several independent studies conclude that haplogroup H probably evolved in West Asia c. 30,000 years ago having arrived to Europe c. 20-25,000 years ago, spreading rapidly to the southwest of the continent. This would make its arrival roughly contemporary with Gravettian culture.
They are also coincident in that the spread of subclades H1, H3 and the sister haplogroup V reflect a second intra-European expansion from the Franco-Cantabrian region after the last glacial maximum, c. 13,000 years ago.
In July 2008, it was published that the ancient mtDNA from an individual whose remains were dated to 28,000 years ago and excavated from Paglicci Cave (Apulia, Italy) had been found to be identical to the Cambridge Reference Sequence in HVR1. The haplotype was different from all persons that had handled the Paglicci 23 remains since their discovery.
Among all these clades, the subhaplogroups H1 and H3 have been subject to a more detailed study and would be associated to the Magdalenian expansion from SW Europe c. 13,000 years ago :
Subhaplogroup H1 encompasses an important fraction of Western European mtDNA, reaching its peak among Basques (27.8%) and being also very important among other Iberians, North Africans and Sardinians. It is anyhow above 10% in many other parts of Europe (France, British islands, Alps, large portions of Eastern Europe) and above 5% in nearly all the continent. Its subclade H1b is most common in Eastern Europe and NW Siberia.
Subhaplogroup H3 represents a smaller fraction of European genome than H1 but has a somewhat similar distribution with peak among Basques (13.9%), Galicians (8.3%) and Sardinians (8.5%). Its importance decreases towards the northeast of the continent though.
The remaining subclades are much less frequent:
Subhaplogroup H5 may have evolved in West Asia, where is more frequent in its non-derived form. But its subclade H5a is most common in the Central European plain.
Subhaplogroups H2, H6 and H8 are somewhat common in Eastern Europe and the Caucasus. They may be the most common H subclades among Central Asians and have also been found in West Asia.
Subhaplogroups H4, H7 and H13 are present in both Europe and West Asia, the latter being also found in the Caucasus. They are quite rare.