The analysis of dozens of ancient genomes extracted from across the vast expanse between Europe and East Asia is shedding light on historical human migration patterns, as well as the spread of Indo-European languages and horse domestication. To date, the earliest known culture to domesticate horses is the Botai, a group that lived on the Eurasian Steppe between roughly 5150 and 3950 BCE. Some have suggested that the Botai were local hunter-gatherers who learnt horse husbandry from a western group of herders who were traveling eastbound; yet, others suggest that the domestication of horses arose locally within the Botai culture. To explore this debate in greater detail, as well as to gain additional insights into ancient human migration patterns, Peter de Barros Damgaard et al. analyzed the genomes of 74 ancient humans who lived between approximately 11,000 and 500 years ago, in Eastern Europe, Central Asia, and Western Asia; as well, the researchers included genetic information from modern-day Asian populations. The authors found little genetic mixing between groups closely related to Eastern European hunter-gathers and the Botai. This suggests that people likely migrated east through the Central Asian Steppe, but did not settle until they reached the more eastern regions, the authors say, meaning that it is unlikely that horse husbandry was brought to the Botai via western populations.
Another highly debated topic is how and when genetic signatures and languages (specifically Indo-European languages) from western regions reached South Asia. Based on their data, Damgaard et al. propose that two waves of genetic admixture occurred. The first wave likely occurred very early, potentially prior to the Bronze Age, and did not include Indo-European speakers; the second group came during the Late Bronze Age (approximately 2300 to1200 BCE), bringing Indo-Iranian languages into South Asia, the authors suggest.