it is notoriously difficult to estimate the ratio of men to women accurately in ancient populations. But if confirmed, one explanation is that the Yamnaya men were warriors who swept into Europe on horses or drove horse-drawn wagons; horses had been recently domesticated in the steppe and the wheel was a recent invention. They may have been “more focused on warfare, with faster dispersal because of technological inventions” says population geneticist Rasmus Nielsen of the University of California, Berkeley, who is not part of the study.
But warfare isn’t the only explanation. The Yamnaya men could have been more attractive mates than European farmers because they had horses and new technologies, such as copper hammers that gave them an advantage, Goldberg says.