My interest in genealogy and RPG’s cross pollinate ideas, like any other interest or experience in life, many things influence our creative ideas.
In late March, there were several articles about a new genetic map of Britain and how it shows that much of the regional populations there is very similar to what it has been for 1,400 years!
I am of Scottish, English, and Irish ancestry, so this resonates with me. It shows that even with the sweep of mass migrations, war, famine, and plague, that populations are resilient. Without massive slaughter, populations may only be pushed out of their exiting area. This would show just how hard it is to wipe out all the humanoids, for example. They might be driven out of the area, but not eradicated without a lot of effort.
Three articles with a bit of different information in each can be found at Medievalist.net, The Independent, and The Telegraph.