[Right Wing Professor]

There really isn't a single useful working definition for a species

Of course there is - a set of organisms which can reproduce and produce viable offspring.

Lions and tigers, by this definition, are the same species, as are horses and zebras. Would you like to try again?

[gore3000]

Of course there is - a set of organisms which can reproduce and produce viable offspring. -me-

Lions and tigers, by this definition, are the same species, as are horses and zebras. Would you like to try again?

Nope, I would not. It just proves my point, looks are deceiving and this is the only objective manner of determining a species. The differences between lions and tigers in looks are far, far smaller than those between a chihuahua and a great dane which no one calls different species.