Early Bronze Age men from the vast grasslands of the Eurasian steppe swept into Europe on horseback about 5000 years ago, and this mostly male migration may have persisted for several generations.
     Europeans are the descendants of at least three major prehistoric migrations. Hunter-gatherers arrived about 37,000 years ago. Farmers began migrating from Anatolia 9000 years ago, bringing their own families. Finally, nomadic herders known as the Yamnaya - an early Bronze Age culture from modern-day Russia and Ukraine - swept in 5000 to 4800 years ago, bringing metallurgy and animal herding skills, and possibly Proto-Indo-European; the ancestral language from which all of today's 400 Indo-European languages descended. They immediately interbred with descendants of both the farmers and hunter-gatherers. Within a few hundred years, the Yamnaya contributed to at least half of central Europeans' genetic ancestry.
     Researchers analysed differences in the ratio of inherited DNA, finding that roughly equal numbers of men and women took part in the migration of Anatolian farmers into Europe, but between five and fourteen men for every one woman in the Yamnaya migration.
     Some researchers warn that it is notoriously difficult to estimate the ratio of men to women accurately in ancient populations. If confirmed, one explanation could be that the Yamnaya men were warriors who arrived on horses, or drove horse-drawn wagons. The Yamnaya men could also have been more attractive mates than European farmers because they had horses and new technologies such as copper hammers.
     The finding that Yamnaya men migrated for many generations may suggests that all was not right back home in the steppe, or it could be that bands of men were being sent to establish new politically aligned colonies in distant lands, as did later groups of Romans and Vikings.

Edited from Science, Popular Archaeology (21 February 2017)