There were clearly multiple waves from multiple origination areas to multiple destination areas with substantial intermixing.
The Neanderthal love tour of Europe is one example.
Vikings and Celts are the result of that.
Do you have any special DNA info or sources for Vikings and Celts? His ancestry was predominantly Scots, but also 1/16th Cree Indian. My late husband was heavily muscled, very strong, light blue eyed, redhead, very hairy, somewhat sunken chin, long torso, short legs, volatile temper, heavy brow ridges. I suspect he was more than 4% Neanderthal, any backup info on that possibility?