Milk is a beneficial food product, but it’s not for everybody. The enzyme that breaks down milk sugar, or lactose, is active in all healthy kids. On the other hand, only a third of adults can consume milk, as a special gene mutation is needed. Other adults can’t digest milk sugar. To them, lactose causes indigestion.
The mutation that enables an adult’s body to break lactose seems to have emerged separately in Europe, Africa and the Middle East. Until now, the genetic origins of numerous milk drinkers living in India was unknown.
Cows enhancing the landscape in southern Estonia. Photo: Jaak Nilson
An international research team at the University of Cambridge tried to answer this question. The team included scientists from the UT Institute of Molecular and Cell Biology and from the Estonian Biocentre.
According to the authors of the study, the multi-millennial cattle-breeding tradition in India had led them to assume a mutation unique to the area.
After analyzing nearly 2,300 gene samples from different areas of India, it was found that the same gene mutation has occurred in India that allows many Europeans to drink milk safely.
“The 13910T mutation, common in Europe, was found in abundance in India too – especially in the areas where milk has been a traditional food product,” explained Toomas Kivisild, coauthor of the study, who works for both Cambridge and Estonia. “The Indian mutation shares origins with the European one.”
An adult who is able to digest nutritious milk has an advantage over others. That’s why the gene variant quickly permeated the population.
According to Mark Thomas from University College London: “The genetic data shows that in the last ten thousand years there hasn’t been a mass migration of people from Europe to India. It seems that the mutation was brought over there by only a few people, which nevertheless caused its quick propagation.”
Still, in India the mutation hasn’t spread into all estates of the realm. The people of South-Indian tribes that don’t breed cattle haven’t got the gene variant. The caste system has probably also hindered the permeation.
Gallego Romero I., Basu Mallick C., Liebert A., Crivellaro F., Chaubey G., Itan Y., Metspalu M., Eaaswarkhanth M., Pitchappan R., Villems R., Reich D., Singh L., Thangaraj K., Thomas M.G., Swallow D.M., Mirazón Lahr M., & Kivisild T. (2011). Herders of Indian and European Cattle Share Their Predominant Allele for Lactase Persistence. Molecular biology and evolution PMID: 21836184
