[<1/1,000,000th%]

The two populations may no longer interbreed, but to me the more important question is this: Are they cross-fertile, and would they produce fertile offspring?

Do you mean like ligers or mules? With enough technology you can cross anything. Look at all the weird lab mice strains running around. Some have human immune systems or human brain cells. ;(

In evolutionary biology, the important first step to speciation is that 2 populations rarely, or don't, crossbreed. That's what allows them to develop separate characteristics and eventually become morphologically distinct and unable to cross-breed.

Your requirements are not part of evolutionary theory.

[Oberon]

Do you mean like ligers or mules?

Actually no, that's not what I mean. I don't know about ligers or tigons, but mules (and hinnies or jennies) are infertile. While donkeys and horses can interbreed, their offspring are not fertile...they're a generational dead-end.

With enough technology you can cross anything.

I'm certain that I disagree with that...but honestly, it requires no great technology to produce a mule. One simply gets a horse and an ass together, and they take care of business in the traditional way.