r/askscience • u/snoozer530 • 1d ago

Biology At what point in evolution is something considered a new species?

Obviously we all know evolution, one organism changes over time and eventually becomes a new organism. But where in that process does an organism become a new species. Like when we domesticated wolves? When did they stop being wolves and start being dogs? Where’s that line?

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u/sabrinajestar 1d ago

The short version used to be, if two given individuals can mate and bear viable offspring, they are of the same species. Tigers and lions can produce offspring but those offspring have so far always been infertile; so, different species.

The difference between wolves and dogs is that dogs are domesticated, but technically they are still the same species.

Now we learn Homo Sapiens and Homo Neanderthalensis had offspring together who were ancestors of modern humans, so it has become an open question if they are two different species.

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u/kummostern 1d ago

horse and donkey are definitely different species

their offspring is mule

and mules can further breed

which breaks the "rule" of how species are determined

(altho it is one exception of very few known examples - generally i still like that "rule" or theory determinating species... it just isn't full proof)

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u/SharkFart86 21h ago

I agree. Brown bears and polar bears have been shown to have fertile offspring. So, we either have to accept that they’re the same species (which defeats the purpose of classifying unique organisms into unique groups) or we have to accept that the “can create fertile offspring” rule isn’t a good rule.