Paleogenetista Carles Lalueza-Fox is currently collaborating with Harvard on a major ancient DNA paper on the population history of the Iberian Peninsula, which is scheduled to be published next year. He was recently interviewed by Spanish Newspaper LaVanguardia about the project. Here are a few interesting quotes (pardon the translation):
And the mixing of genes continued...
Yes, 4,000 years ago came the Kurgan people, who domesticated the horse on the Pontic-Caspian Steppe and spoke Proto-Indo-European, the ancestral language to Celtic, Latin, Greek...their impact on our DNA was high.
What does that mean?
Their numbers grew at the expense of the previous population: today the Kurgan genetic footprint makes up 40% of the Western European genome!
Also in the Iberian peninsula?
Fifty per cent of our ancestry is derived from Neolithic farmers, 30% from the Kurgan people and 20% from hunter-gatherers.
Note the date: 4,000 years ago. That's not a Bell Beaker date, it's an Atlantic cist tradition date. What the hell is the Atlantic cist tradition, you're probably asking. Have a look at the video here, or, if you're too lazy, this screen cap.
Yamnaya-related admixture in Bronze Age northern Iberia