“This is a really exciting paper,” says Priya Moorjani, a geneticist at the University of California, Berkeley, who notes that the field of ancient DNA is moving so quickly that every study reveals something new. Yet other researchers caution that the debate isn’t anywhere near settled.
The first signs of horse domestication—pottery containing traces of mares’ milk and horse teeth with telltale wear from a riding bit—come from the Botai hunter-gatherers who lived in what is now Kazakhstan from about 3700 B.C.E. to 3100 B.C.E. Yet some researchers thought the isolated Botai were unlikely to have invented horse husbandry because they kept to their hunting and gathering ways long after their neighbors had adopted farming and herding.
These researchers assumed the Botai must have learned to handle horses from the Yamnaya, their neighbors to the west who were already herding sheep and goats. As part of the “steppe hypothesis,” the Yamnaya also migrated east and west during the Bronze Age, mixing with locals and spreading genes found in ancient and modern European, Central Asian, and South Asian populations. Some researchers hypothesize that they also spread early branches of the hypothesized Proto-Indo-European (PIE) language, which later diversified into today’s Indo-European languages, including English, Italian, Hindi, Russian, and Persian.
To explore the Yamnaya’s legacy in Asia, a team led by geneticist Eske Willerslev of the University of Copenhagen and the University of Cambridge in the United Kingdom sequenced the whole genomes of 74 ancient Eurasians, most of whom lived between 3500 B.C.E. and 1500 B.C.E. Bodies included people from both the Botai and Yamnaya cultures, among others. The researchers devised a rough family tree, which they extended using samples from modern and ancient people.
The new work fits well with a recent study of ancient horse DNA, says zooarchaeologist Sandra Olsen at the University of Kansas in Lawrence, a co-author on that study. Her work showed that Botai horses were not related to modern horses, hinting at separate domestications by the Botai and Yamnaya. Yet certain practices of the Botai—specifically the way in which they ritually buried slaughtered horses—are shared by other cultures in Asia, hinting that perhaps the hunter-gatherers weren’t as isolated as most have thought, she says.
Whatever happened in the early days of horse husbandry, it’s clear the Yamnaya took advantage of the beasts in ways the Botai never dreamt of. Beginning in the early Bronze Age, the pastoralists used their horses to migrate far and wide.
Traces of west Eurasian genes in Asian populations has been taken as evidence the Yamnaya left a large genetic legacy east of the steppe. Yet Willerslev’s team found little Yamnaya DNA in Central and South Asia—and none in Anatolia. Instead, their data suggest the Namazga, a group of herders living south of the steppe around 3300 B.C.E., before the great Yamnaya migration, were the ones who first contributed west Eurasian genes to Asian populations.
That lack of a genetic legacy may put leading theories for the spread of PIE at risk. The ancient people of Anatolia in modern Turkey, for example, likely spoke Hittite, a very early branch of PIE. But the lack of Yamnaya DNA among the Hittites suggests some other group brought Indo-European to the region—and to Central and South Asia.
The findings are impressive in some ways and frustrating in others, notes Paul Heggarty, a historical linguist at the Max Planck Institute for the Science of Human History in Jena, Germany. On the one hand, he credits the authors for reconsidering the origins of Hittite in light of the new data. “This is the first time I’ve seen people who have supported the steppe hypothesis … saying, ‘Look, it doesn’t work for Anatolia,’” Heggarty says. Other researchers should take the next step, he adds, and continue searching for the origins of PIE beyond the steppe.