M24

Origins and Evolution

mtDNA haplogroup M24 is a subclade nested within the broader South Asian lineage M2, itself a branch of macro-haplogroup M. Based on its phylogenetic position and observed diversity, M24 most likely arose in the South Asian subcontinent during the Upper to Late Paleolithic (tens of thousands of years ago), following the early expansion of M-bearing maternal lineages into South Asia. Its age is younger than the parent M2 (commonly estimated near ~50 kya), and molecular-clock based inferences place M24's origin in the later Upper Paleolithic (roughly on the order of ~20–40 kya), consistent with localized diversification after the initial settlement of the region.

Subclades

M24 shows limited but detectable internal diversity in population surveys and full mitogenome studies, indicating the presence of localized sublineages that are often rare and regionally restricted. Sampling is still sparse compared with major M subclades, so some smaller subclades may be private to particular tribal groups or geographic pockets. Targeted whole-mitogenome sequencing in understudied South Asian populations is likely to clarify named subclades and the internal branching of M24.

Geographical Distribution

The distribution of M24 is concentrated in the Indian subcontinent with highest frequencies and diversity among indigenous (Adivasi/tribal) groups and some Dravidian-speaking populations of South India. It is observed at lower frequencies in Indo-Aryan speaking populations of northern and central India and is occasionally detected in adjacent regions such as Sri Lanka, Bangladesh, Nepal and parts of Pakistan. Sporadic occurrences in nearby Southeast Asian populations have been reported, consistent with historical and prehistoric gene flow across the Bay of Bengal and along coastal routes. The overall pattern points to long-term local continuity with limited but detectable regional mobility.

Historical and Cultural Significance

Because M24 is principally found among indigenous and longstanding South Asian populations, it contributes to the genetic signature often interpreted as pre-Neolithic and local maternal continuity in the subcontinent. Its persistence through time implies that female lineages carrying M24 were part of the demographic substrate encountered by later cultural complexes (for example, Neolithic agricultural communities and the urbanizing populations associated with the Indus Valley/Harappan tradition). While not diagnostic of any single archaeological culture, M24 is consistent with a model in which Paleolithic and Mesolithic maternal lineages remained present and admixed with incoming groups during Neolithic and Bronze Age transitions.

Conclusion

M24 is a regionally focused South Asian mtDNA lineage descended from M2 that reflects long-term maternal presence and local diversification within the Indian subcontinent. Its relatively low to moderate frequency and patchy distribution emphasize the importance of dense sampling and mitogenome sequencing in tribal and understudied populations to fully resolve its phylogeny and migratory history. Continued work integrating ancient DNA, high-resolution mitogenomes, and archaeological context will refine age estimates, subclade structure, and the role of M24 in South Asia's prehistoric population dynamics.