re: Why do Bristish people historically have bad teeth???

There may be a genetic component but largely it seems to be a cultural thing because the younger generations are "normal." Spain was kinda similar. I remember in the early 90's there were people on tv in Spain missing front teeth and it was no big deal. Today that may not be the case.

Inbreeding was normal all over the world and isn't bad in a homogeneous population so we can rule that out. Traveling was hard to do before the horse and buggy. Most bred with others in the same villages. Marrying your cousin was not taboo.