"Europeans today are a mixture of three very different ancestral populations: hunter-gatherers, first farmers, and a population with eastern affinities that was not yet present in Europe at the time of the first farmers. It was unclear when and how this eastern component arrived in Europe... ‘When we first looked at the new data, it was a Eureka moment’ ... ‘The eastern ancestry was present in every single sample starting at around 4,500 years ago, and absent in every single one before that time.’"