Yes, evidently the ones with the lower IQs.
Even if the Machiavellian intelligence hypothesis is correct, it isn't invulnerable to selective forces pushing in the other direction, like parasite load, lack of resources, small founder populations, island dwarfism, and so on. We've seen the Flores hominids, we know it happened.
Human intelligence won't miraculously keep increasing in any and all environments. Lack of genetic diversity doesn't factor into it.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.