Convergent evolution & interbreeding?

[Lurker]

Ok I know this is a very odd question, but … I have been reading some Sci Fi game rules (Star Trek & Star Wars mainly) and I’ve been thinking about race interbreeding.

Considering, in a sci fi setting, you have multiple races and some of them are bound to be convergent evolution wise. So, could those races successfully inter breed? Of course, that is a no for the divergent species nor ones from un similar foundational type, however, for the species that come from similar ‘types’ of …stock … and evolve into the same niche …

I know the default answer will be “whatever you want for the setting to make it a fun game”. However, what is a semi-scientific answer to it?

[Arduin]

Homo sapiens & Homo neanderthalensis successfully interbred.

[Treebore]

They would have to be pretty close, and even if they are, if its been less than, say 5,000 years since they last "crossed", then yes, very possibly, but if its been over 5,000 years, it would be more scientific to say they can't. Why? Because in 5,000 years worth of generations their genetics have simply diverged too greatly. Unless its a race that is very simple, genetically speaking. Then you could get away with saying that they can successfully mate with a closely related species. You could even say, their genetics have remained so simple in order to allow them to breed with most anything. Hmmmm... it would be an interesting thought exercise to create a world where a race needed such a mechanism...