Cyrus, it\'s a generally accepted definition in biological sciences. If two individuals can procreate and produce fertile, healthy offspring (all the time over all generations, not rarely) then they are considered to be from the same species. It\'s not uncommon that two species, that lay close together on the ladder of evolution can still procreate but their offspring will normally be infertile. This is the case with a donkey and a horse, resulting in mules. Mules cannot survive on their own for X number of generations, rarely can they produce another generation but then it will stop there.
I don\'t know why this discussion is kept here ... or why it is even kept at all. The definition of what different species are is correct, check any decent biology manual. Race has not much to do with it though, since that is just a label given to visually different individuals of the same species.
Lets not nit-pick at rules that were made long before us by people who did a whole lot more research into the matter and get back on topic here?