M37

Origins and Evolution

mtDNA haplogroup M37 is a subclade nested within the South Asian M3 lineage of macro-haplogroup M. Given the parent M3's estimated emergence around ~25 kya and the typical branching patterns observed in South Asian M subclades, M37 most plausibly coalesced in the Late Pleistocene to the early Holocene (we estimate ~15 kya). Its emergence reflects the deep maternal diversification that occurred in South Asia following the initial expansion of macro-haplogroup M out of the initial dispersal corridors of modern humans.

The phylogenetic position of M37 as a derived branch of M3 suggests it arose through localized mutation(s) in a maternal population that was already well-established in the subcontinent. Subsequent demographic processes — including founder effects, genetic drift within small and often endogamous groups, and limited regional gene flow — have shaped the modern distribution and frequency of M37.

Subclades

At present, published datasets and regional sequencing surveys indicate M37 is represented by a small number of identifiable internal lineages (sometimes reported in the literature as minor sublineages or private mutations). High-resolution whole-mitogenome sequencing in additional South Asian populations is needed to resolve any named subclades (for example, hypothetical M37a/M37b designations) and to establish a detailed substructure and age estimates for those branches. Until more complete mitogenomes are sampled, M37 should be treated as a regionally restricted lineage with limited documented internal diversity.

Geographical Distribution

M37 is concentrated in South Asia, where it has been reported at low to moderate frequencies among several tribal groups and some caste populations across India. The lineage also appears at lower frequencies in neighbouring countries (Sri Lanka, Pakistan, Bangladesh, Nepal) and in a small number of Southeast and Central Asian samples, consistent with historical and prehistoric gene flow across the region. A small number of identifications in Indian Ocean rim island populations and very low-frequency occurrences in modern diaspora communities outside Asia have been recorded. In the referenced database M37 appears in 2 ancient DNA samples, indicating archaeogenetic continuity in at least some local contexts.

Historical and Cultural Significance

Because M37 is primarily South Asian and relatively low-frequency, it most plausibly represents a legacy of pre-Neolithic and early Holocene maternal lineages that contributed to the modern genetic landscape of the subcontinent. Its presence among tribal groups is consistent with continuity from Mesolithic hunter-gatherer communities and subsequent incorporation into Neolithic and Bronze Age societies. M37 can therefore be informative in studies that seek to distinguish deeper regional maternal continuity from later demographic inputs (e.g., Bronze Age migrations or historic-era movements).

M37 has not been strongly associated with any single pan-regional archaeological culture the way some steppe-related lineages are with Yamnaya or Corded Ware; rather, its pattern fits a model of long-term local persistence with sporadic spread into neighbouring populations through trade, migration, and admixture.

Conclusion

mtDNA M37 is a South Asia-centered maternal lineage derived from M3, reflecting deep regional maternal diversification in the Late Pleistocene–early Holocene. It remains a useful marker for reconstructing local population continuity and microevolutionary processes in the subcontinent, but its low frequency and limited sampling mean that further high-resolution mitogenome data are required to fully resolve its internal phylogeny and finer-scale demographic history.