Why can some species cross breed but their offspring are not fertile?! (eg. a horse and a zebra can haev a foal but it

Why can some species cross breed but their offspring are not fertile?! (eg. a horse and a zebra can haev a foal but it can’t reproduce) if it can work once, why not twice?

Posted on June 20, 2013 by in Question. Comments Off on Why can some species cross breed but their offspring are not fertile?! (eg. a horse and a zebra can haev a foal but it