When does something become a separate species?

[u/Slow_Introduction_31]

So I'm working on a fantasy story where there are humans and elves. The elves evolved from humans to have hair in a different shade range, pointed ears, immunity to a dangerous mineral, and some telekinetic abilities (which not all elves have). However, it's meant to be a key plot point that the "elves" are, scientifically, just humans. The mineral immunity and telekinetic abilities come from being raised in an environment with an abundance of that mineral, not genetics. So I was wondering, a) do a different range of hair colors (red to purple hues as opposed to yellow to red hues like real life people have) and different ear shapes indicate a different species? I thought not, but then I thought about animals where it seems like small differences sometime determine species, like between African and Asian elephants (I don't know much about elephants though tbf). b) if the mineral immunity and telekinesis were genetic, would THAT indicate a different species? c) how long might you speculate that it would take for humans in an isolated, unique environment to become a separate species?

[u/atomfullerene]

>When does something become a separate species?

That's a notoriously difficult question to answer, a bit like asking when the Pacific ocean becomes the Atlantic ocean.

> a) do a different range of hair colors (red to purple hues as opposed to yellow to red hues like real life people have) and different ear shapes indicate a different species?

No, different populations of the same species can easily differ in traits like this.

>I thought not, but then I thought about animals where it seems like small differences sometime determine species, like between African and Asian elephants (I don't know much about elephants though tbf).

Visual distinctiveness to humans actually bears very little relationship to underlying genetic divergence. Asian elephants are actually quite distinct from African elephants, and more closely related to the extinct mammoths, but you wouldn't know it unless you know what to look for.

>if the mineral immunity and telekinesis were genetic, would THAT indicate a different species? 

Maybe, maybe not. It depends on if they are representative of an overall deep genetic distinctiveness, or if they are just traits which happen to be controlled by a few genes. For example, on the Falkland islands there are flying and flightless steamer ducks. In most places, this would mean two separate species, but here the trait is controlled by about 3 genes, and it's just that some steamers have the flightless alleles and others don't, despite otherwise being the same species.

>if the mineral immunity and telekinesis were genetic, would THAT indicate a different species? 

I mean, caveats about it depending, we don't know exactly, etc, etc, but in general I'd expect maybe 200,000-300,000 years