Yes, a study of Neanderthal DNA actually suggested that inbreeding and lack of genetic diversity may have contributed to the decline of the Neanderthals. As for French Canadians, there's certainly an issue with inbreeding and recessive illnesses in relatively isolated communities such as those in the Saguenay region. It isn't really an issue in more urban areas and less isolated rural areas, because of immigration over the years, settlers from England and Scotland, and also huge numbers of Irish orphans being adopted by French Canadian families during the Irish Potato Famine. The Irish children were sent to French families because the orphans were almost all Catholics, and mostly grew up speaking French and carrying the names of their adoptive families, but they did inject a lot of new blood into Quebec, even if the Irish peasants at that time were probably quite inbred themselves. There's a big problem with inbreeding and recessive diseases in Newfoundland and Labrador, where most people are descended from settlers who moved there during the period 1400 - 1600 AD - the Bristol merchants were fishing in Newfoundland and even settling there before Columbus, although they were initially very secretive about it, to protect their source of cod. So pretty much everyone in Newfoundland is related to everyone else, except for the small minority who've settled there in the last 100 years or so. And of course the inbreeding of the European royals is a whole saga in itself.