People often think that Europeans are homogeneous group that arrived in a simple way there maybe 40 or 50 thousand years ago maybe based on the archaeology and just kind of sat there until they became the Europeans they are today, but that's probably not true: the Europeans today are a replacement population who came in much more recently and replaced the people who were there originally 40 thousand years ago.

History Aids Understanding Diseases Today, National Science Foundation, 20 July 2012