M45

Origins and Evolution

Haplogroup M45 is a descendant lineage within the M4 subclade of the macro-haplogroup M, which itself represents one of the major non-African maternal branches that diversified soon after modern humans dispersed out of Africa. Based on the phylogenetic position beneath M4 (a South Asian-centered clade dated to the Upper Paleolithic), M45 most likely originated in South Asia during the Late Upper Paleolithic (roughly estimated here at ~18 kya). This timeframe places its origin after the initial arrival of M-bearing lineages in South Asia and plausibly during the period of post-glacial demographic adjustments and localized expansions of hunter-gatherer groups.

Phylogenetic resolution for many M4-derived lineages is still incomplete in the literature: most inferences about M45 are drawn from control-region and partial coding-region data, while full mitogenome sequencing is required to define finer substructure and to refine age estimates. As with many South Asian M subclades, M45 probably reflects an early regional differentiation event followed by long-term local persistence and later low-level gene flow into adjacent regions.

Subclades (if applicable)

Detailed, well-supported downstream subclades of M45 remain understudied or sparsely sampled in published datasets. Where reported, putative downstream lineages are typically defined by a small set of coding-region mutations; however, broad geographic sampling and whole-mitochondrial-genome data are needed to confirm and name robust subclades. In practice, research to date treats M45 as an intermediate clade connecting M4 and more localized maternal lineages present among tribal and regional populations in South Asia and adjacent highlands.

Geographical Distribution

The distribution of M45 mirrors that of many M4-derived lineages: highest frequencies and diversity in South Asia, especially among indigenous tribal and some caste groups, with reduced presence in Himalayan margin populations and sporadic low-frequency occurrences in neighboring regions. Reported geographic patterns include:

• Concentration in tribal and indigenous populations across the Indian subcontinent (particularly in central and southern India).
• Presence in broad caste and general-population surveys across North and South India at lower frequencies.
• Occasional detection among Nepali and Himalayan-adjacent groups (including edge populations near the Tibetan Plateau).
• Low–moderate frequencies in parts of Pakistan and Sri Lanka, and rare examples in Bangladesh and eastern India.
• Scattered, low-frequency occurrences in Myanmar and adjoining Southeast Asian samples, and sporadic reports in select Central Asian datasets.

These patterns suggest an origin and long-term continuity within South Asia, with limited dispersal into neighboring regions driven by small-scale migrations, trade, and highland population movements rather than large demographic replacements.

Historical and Cultural Significance

Because M45 predates major Holocene cultural complexes, its primary significance is as a marker of pre-Neolithic and Mesolithic maternal ancestry in South Asia. It likely persisted through major cultural transitions (local Mesolithic -> regional Neolithic developments -> Bronze Age urbanization) and therefore contributes to the genetic substrate underlying many later South Asian populations.

• In archaeological contexts, M45 and related M4 lineages are most plausibly associated with the indigenous hunter-gatherer and early food-producing communities of South Asia rather than with later steppe-derived migrations.
• During the Neolithic and Bronze Age (including the time of the Indus Valley/Harappan civilization), M45 lineages would have been part of the regional maternal pool interacting with local innovations and demographic shifts.
• The haplogroup provides useful information for reconstructing the deep maternal ancestry of South Asian tribal groups and for differentiating local continuity from later immigrations.

Conclusion

mtDNA haplogroup M45 represents a South Asian-centered maternal lineage nested within M4, with an Upper Paleolithic origin and a present-day distribution concentrated in indigenous and regional populations of South Asia and adjoining highland and peripheral regions. Continued whole-mitogenome sequencing and denser geographic sampling are needed to resolve its internal structure, refine its age, and clarify the micro-histories of its dispersal into neighboring regions.