Genetic Clues From South Asia Explain Milk-Drinking Ability
A new genomic study reveals intriguing insights into why many adults in South Asia — the world’s largest dairy producing and consuming region — remain largely lactose intolerant, yet certain populations have developed a strong ability to digest milk into adulthood.
Despite the subcontinent’s deep cultural and dietary association with dairy, most adults in India, Pakistan and Bangladesh do not produce enough lactase, the enzyme needed to digest lactose — the sugar found in milk — beyond infancy. As a result, many traditional dairy foods in South Asia are fermented or processed (like yogurt, ghee and paneer) to reduce lactose content and make them easier to digest.
Researchers from the University of California, Berkeley analysed around 8,000 modern and ancient genomes from across the region to understand the evolutionary history of lactase persistence — the ability to continue digesting lactose into adulthood. They focused on the genetic variant known as −13,910*T, which in many global populations is linked with sustained lactase production.
The study found that this milk-digesting gene variant was introduced into South Asia during historic and medieval periods, likely linked to migrations from steppe pastoralists, but it did not spread widely across most populations as it did in Europe. In most groups, the prevalence of the gene largely mirrors ancient ancestry rather than broad natural selection across the region.
However, an exception emerged in two traditional pastoralist communities — the Toda of South India and the Gujjar of northwest India and Pakistan — where lactase persistence reaches unusually high levels (up to ~90%). This suggests that lifestyle and prolonged reliance on fresh dairy products exerted strong evolutionary pressures in these herding populations, enabling sustained milk digestion into adulthood.
The findings highlight that the evolution of lactase persistence is multifaceted, shaped by ancient migrations, culture, diet and ecological history, rather than a single narrative of adaptation. Understanding this complex genetic landscape provides fresh perspectives on human dairy consumption patterns and nutritional biology.
Source : Dairynews7x7 Dec 30th 2025 Read full story here