[toast]

I thought one of the definitions of a separate species was that two different parent species could not produce fertile offspring.

How could they co-mingle the 2 species?

[KarlInOhio]

I thought one of the definitions of a separate species was that two different parent species could not produce fertile offspring. How could they co-mingle the 2 species?

If you could find evidence that either they could breed together or couldn't, then you would answer the question of whether they are separate species. We don't know for sure, so all else is speculation.

I don't think that genetic science has advanced far enough to tell just from DNA samples whether two close samples could interbreed or not.

[Wolfstar]

I thought one of the definitions of a separate species was that two different parent species could not produce fertile offspring.

That's a common, but incorrect, understanding of the term. Merriam-Webster defines the word "species" as follows:

A category of biological classification ranking immediately below the genus or subgenus, comprising related organisms or populations potentially capable of interbreeding, and being designated by a binomial that consists of the name of a genus followed by a Latin or latinized uncapitalized noun or adjective agreeing grammatically with the genus name.

[brytlea]

I used to think that too, but apparently it’s not correct. Lions and tigers can produce fertile offspring, as can cattle and bison (to name a couple of instances). To me, the definition of species is a little fluid, since I KNOW I was taught (and taught when I taught HS biology) that if 2 creatures could breed and produce fertile offspring they were the same species.
susie

[allmendream]

A species is a population of interbreeding individuals.

Two separate species may well be CAPABLE of interbreeding and producing fertile offspring but if they do not, and according to genetic research have not for several thousand years; they are a separate species even if you can successfully breed them in captivity.