3 ms·

It's a bit more specific actually: this thing can't mate with that thing and produce viable offspring.

• ravenstine 7y ago
  In practice, that is often not the case. Most species haven't been tested to see whether they can produce viable offspring with each other(it's usually impractical), and there are plenty of different species known to breed successfully with one another. Mules, horse-donkey hybrids, while the vast majority of them are infertile, are considered different species. Camels and Llamas can produce viable offspring even though they evolved on two different continents.
  • ses1984 7y ago
    Most species don't really need to be tested because their chromosomes are different enough to make it obvious their offspring would be infertile, right? Of course if hybrids are infertile they would be considered different species. If hybrids are fertile, like your example of camels and llamas, then according to what reason would they be considered the same species? Did their evolution diverge and then reconverge? I guess it depends on your definition of "often".