[muawiyah]

Horses and men are both able to produce viable gametes. That doesn't mean you can cross breed them to get a viable embryo.

Obviously that could be interpreted as sterility ~ NO VIABLE EMBRYO ~ which is, of course, just that.

You can also have Viable Embryos that themselves are unable to produce useful gametes.

I think you slipped a cog here.

Or, you and I may be reading the same scientific language version of the same material differently. To dispel doubts here's a POP SCIENCE version: http://www.sciencenews.org/view/generic/id/339172/title/Geneticists_go_ape_for_better_primate_family_tree

[allmendream]

Way to not understand my point.

Meiosis is necessary to create viable gametes. Both horses and men produce viable gametes because meiosis isn't a problem when their parents are the same species - but those viable gametes cannot, when combined, produce a viable embryo.

A horse and a donkey produce viable gametes - AND they produce a viable embryo - but when that embryo grows into a mule and attempts to undergo meiosis to produce viable gametes - it runs into difficulty.

Follow?

Meiosis isn't a problem in the mule, and doesn't stop it from becoming an ADULT - it stops it from being fertile (usually).

Even if meiosis between a donkey chromosome and a horse chromosome was COMPLETELY unable to happen - horse and donkey cross breeds would still be sterile mules.

Your source doesn't claim what you claim.