You don't need a lot of territory for this to happen. The lice that specialize in humans have split into two distinct species: one for head hair and one for pubic hair. (and allegedly the latter is under threat).
Can we, uhh, not mention this to any alien species we may encounter in the future?
Human head and body lice have indeed diverged, but are not completely speciated and can, in the lab, still interbreed. The term in the Wikipedia was "subspecies"; as I'm not a zoologist I'm not sure if it's a formal term or not.
But my claim head/pubis claim was wrong. That's my TIL for today!
Can we get an endangered-species designation asap? I've shorted Gillet's stock.
Not that many centuries. Australia was colonized very recently. Go to placed like the middle east or china and families may have been in the same area for thousands of years.
It's an anecdote, but I was pretty impressed when my uncle recently signed up for one of those ancestry tests, and it correctly pinpointed exactly the region that his grandfather (my great-grandfather) had come from in the late 19th century. I'm certainly no expert in the genetics but it boggles my mind a bit that it's detectable that his recent lineage didn't stray much from that small area of Europe until it went to the States. I share 50% of my ancestry with him, the other 50% is from other parts of Europe, my wife is from another part with its complicated story, and we have kids... After 3 generations I don't think any one particular country should be particularly recognizable (though I'll admit, I may be over-simplifying or misunderstanding how it works). Yet my uncle's DNA test pinpointed a small place in Europe with only a few hundred thousand people, and did so correctly.
I am really pleased by the human borough/rat burrow parallel here.
A rat living in the city has it pretty good compared to those that have to forage in the wild. Slices of pizza regularly fall onto the subway tracks, for example, but this really doesn't happen in the middle of the forest. Nobody leaves huge dumpsters full of food scattered across the countryside, but they're literally on every single street corner in a city like New York.
They were just carried there. They are rather smart, but either way will do what they can to find food and mates, just like every other species.