A mass migration of males transformed the genetic make-up of people in Spain during the Bronze Age, a study reveals, BBC reports.
DNA evidence shows the migrants streamed over the Pyrenees, replacing existing male lineages across the region within a space of 400 years.
It remains unclear whether there was a violent invasion or whether a male-centric social structure played an important role.
The result comes from the most extensive study of its kind.
Researchers reconstructed the population history of Iberia (modern Spain and Portugal) over 8,000 years - the biggest slice of time tackled by ancient DNA research.
Their study is published in Science journal.
They extracted and analysed DNA from 403 Iberians who lived between 6,000 BC and AD 1,600.