So this is a bit of Big Up History, but that's cool. Right, so Germans (and Dutch and Danish) people came to England about 1600 years ago. They were the Anglo-Saxons. The current English population is pretty Anglo-Saxon. BUT not very many Anglo-Saxons came over - not enough to explain why we're all so pallid and mousy brown and blue-eyed. Historians have grumbled over this for a while, but now Science saves the day and explains why the German genes are so predominant.
It's not all that nice a reason - seems those Anglo-Saxon types set up a kind of apartheid whereby the incoming, wealthy, boisterous A-S types were able to out-breed the dull, slow-witted native Brits (called Welshmen, even the ones in England -who knows why). The Welshmen weren't allowed to marry the Anglo-Saxons, and the economic advantage of the incomers (good at making sausages, reliable carts etc) meant that their genes won out.
This apartheid solution was hit upon by Mark Thomas at UCL by computer modelling the populations of A-S vs Welshmen - the apartheid model was the only one that fit the high proportion of Anglo-Saxon Y chromosomes in the English population. This was published in the Proceedings of the Royal Society B [doi:10.1098/rspb.2006.3627].
The most interesting thing about this story is that the Scientician and I met Dr Thomas in a bar in Copenhagen a few years ago, and talked at him drunkenly about science. *That* is a fact.