The Paleogenomics of Rakhigarhi: Triangulating Ancient DNA, Starch Granules, and Harappan Continuity

In 2019, a research team led by archaeologist Vasant Shinde and geneticist Vagheesh M. Narasimhan published the first successful sequencing of an ancient genome from the Indus Valley Civilization (Cell). Extracted from a woman buried in the Mature Harappan cemetery at Rakhigarhi, Haryana—cataloged in genetic datasets as individual I6113—the sample yielded ancient DNA (aDNA) despite the high heat and humidity of lowland South Asia, which typically degrades organic matter (ScienceAlert).

When paired with microscopic starch granule analysis from dental calculus (calcified tooth plaque) and ceramic vessel residues across Harappan sites, individual I6113 provides a empirical baseline for discussing both population genetic continuity and agricultural subsistence in Bronze Age South Asia.

Genetic Architecture of Individual I6113

The sequencing of individual I6113, detailed by Shinde et al. in Cell, revealed a genetic profile composed of two primary deep ancestral lineages: an Iranian-related hunter-gatherer component and a South Asian hunter-gatherer component linked to Ancient Ancestral South Indian lineages.

Crucially, the statistical modeling performed by the team showed that the Iranian-related lineage in individual I6113 split from Western Iranian hunter-gatherers and agriculturalists prior to the emergence of farming in the Fertile Crescent. This finding indicated that early farming in northwest South Asia did not require a massive demic diffusion (population migration) of Western Asian farmers. Instead, local populations adopted or independently developed agricultural practices.

Furthermore, individual I6113 carried no detectable Steppe pastoralist-derived genetic ancestry. This specific ancestry profile matched 11 genetic outlier individuals previously recovered from sites in Iran (such as Shahr-i Sokhta) and Turkmenistan (Gonur Depe) that shared documented trade links with the Indus Valley Civilization (Cell).

⚖ Scholarly Debate: The Timing of Steppe Ancestry Arrival

The absence of Steppe pastoralist ancestry in the Rakhigarhi genome (~2500–2000 BCE) sits at the center of ongoing demographic debates regarding post-Harappan South Asia.

• The Migration Model: In a companion paper published simultaneously in Science, Narasimhan et al. analyzed ancient genomes across Central and South Asia. The researchers argued that Steppe-derived pastoralist ancestry entered South Asia in the early second millennium BCE (between 2000 BCE and 1500 BCE), after the peak of the Mature Harappan period. According to this model, gene flow from the Eurasian steppe mixed with local Indus Valley populations, shaping the genetic structure of modern South Asian groups and serving as a vector for Indo-European languages.
• The Indigenous Development Model: Alternative scholarly perspectives emphasize long-term biological and cultural continuity within the Indian subcontinent. Proponents of these models argue that the single dataset from individual I6113 demonstrates that the urban Harappan core developed without relying on incoming migrations from the Eurasian Steppe or Western Asia. Some scholars caution against drawing sweeping linguistic or demographic conclusions from a limited number of ancient genomes, suggesting that regional population density and local population movements could account for genetic variations observed in later historical periods.

Microfossil Evidence: Starch Granules and Botanical Diet

While paleogenomics isolates population history, paleobotanical residue analysis documents daily diet and land use. Analyzing plant microfossils—specifically starch granules trapped in human dental calculus and absorbed into the clay matrix of unglazed cooking vessels—allows archaeobotanists to identify plant taxa at the species or genus level.

Starch granule analysis operates by examining the microscopic structures formed inside plant plastids. Characteristics such as granule size, shape (e.g., spherical, polyhedral, or lenticular), hilum position (the growth point of the granule), and the presence of extinction crosses under polarized light microscopy serve as diagnostic features (Frontiers in Ecology and Evolution).

Complementing genomic data from Rakhigarhi, microfossil residues and lipid analyses from Harappan ceramics—such as those conducted by Akshyeta Suryanarayan et al. across settlements in Haryana including Rakhigarhi, Farmana, and Masudpur—demonstrate a multi-cropping agricultural strategy:

1. Winter Crops (Rabi): Microfossil evidence confirms the processing of broad-grained cereals such as barley (Hordeum vulgare) and wheat (Triticum species), inherited from early Holocene agricultural developments.
2. Summer Crops (Kharif): Starch granule recovery from tooth calculus highlights the consumption of small-grained summer crops, particularly native and introduced millets (such as Brachiaria and Setaria) alongside pulses.
3. Processing and Consumption: Intact and gelatinized starch granules recovered from ceramic interiors show that grains were ground using querns, boiled into gruels, and cooked alongside animal fats, reflecting complex food processing routines adapted to seasonal monsoon variations.

Triangulating Genes, Food, and Continuity

By combining ancient genomic sequencing with botanical residue microfossils, researchers construct an empirical framework for understanding the Indus Valley Civilization.

The DNA from individual I6113 confirms a local genetic foundation that persisted through the urban peak of the civilization. Concurrently, starch granule microfossils illustrate a flexible dietary strategy that integrated local wild plants, native domesticates, and winter cereals. Together, these scientific methods allow archaeologists to trace population continuity and environmental adaptation in Bronze Age South Asia directly from physical remains.