Researchers have gleaned new insights into India’s evolutionary history after conducting the largest genome study of its kind.

Scientists analyzed more than 2,700 modern Indian genomes from 17 states, including DNA from individuals from most geographic regions, speakers of all major languages, tribal and caste groups. They revealed that one of the three main ancestral groups in India — ancient Iranian farmers — can be traced back to a group of agricultural farmers from Sarazm in modern-day Tajikistan. They also uncovered the extraordinary diversity of DNA inherited from Neanderthals and Denisovans, the closest, now-extinct relatives of modern humans.

Additionally, the team found that most of the genetic variation within the current Indian population stems from a single, major migration event of modern humans to India from Africa around 50,000 years ago. The researchers described their findings in a preprint paper published on the bioRxiv database. “South Asian populations are often underrepresented in genomic studies,” Elise Kerdoncuff, lead study author and a population geneticist at the University of California, Berkeley (UCB), told Live Science in an email. “Studying Indian populations helps us understand the history of India, and as our study demonstrates, it also provides valuable insights into broader aspects of human history.”

Home to more than 1.4 billion people, India is one of the most populated countries in the world, with more than 4,500 anthropologically well-defined populations, including castes, tribes and religious groups. However, despite this extensive diversity, Indian populations have often been underrepresented in genomic studies, which have primarily focused on people of European ancestry.

To paint a clearer picture of genetic variation in India, the authors of the new study analyzed the genomes of thousands of individuals who participated in the Longitudinal Aging Study in India-Diagnostic Assessment of Dementia (LASI-DAD). Participants were over the age of 60 and agreed to have blood samples taken for analysis.

Most Indians derive ancestry from three ancestral groups: ancient Iranian farmers, Eurasian Steppe pastoralists and South Asian hunter-gatherers. Researchers already understood how the latter two groups came to India, but they didn’t know how and when DNA from ancient Iranian farmers arrived in the region, co-senior study author Priya Moorjani, an assistant professor of genetics, genomics, evolution and development at UCB, told Live Science in an email.