Cotter -
I don't know, but I did a search for a global map of where monkeys live (and all non-Homo primates for that matter), then examined that with an eye towards the location of the equator and the band of northern and southern deserts that are about 30 degrees N/S of the equator. That gives me an idea ... could be right, could be wrong. I don't think there's much territory non-human primates are adapted to that they aren't using that isn't closed to them by expanses of desert lacking food / water / cover for them.
Genus Homo, though? Well, Neanderthals were cold-adapted, they didn't get forced out / killed off by cold in the north, they were already there ... and stayed. Our ancestors overcame conditions through use of tools and gathering food, then carrying it. What's left? Bigfoot, right? If they are what I think they are, so far as ecological niche, I think they're likely the North American equivalent of the Neanderthals in Europe and maybe Asia. No adaptation needed, no return immigration needed, they were already here and doing fine.
Leaves a lot painted, or assumed painted , with that "very broad brush", but on a broad brush scale it works.
MIB