if we differentiate between species by not being able to provide fertile descendents. Why do we say neanderthals were a different species from us but also say we got some of their genes via cross reproduction?
In: Biology
There are several different criteria to differentiate species. There are scientist who advocate for stricter criteria, and there are scientist who advocate for looser criteria. I’ll name just a few that come to mind.
* Fertile offspring: Some animals can create offspring, but they’re not fertile. The classic example is the mule. They are not considered the same species.
* Lock and key: Some insects can produce fertile offspring, but their sexual organs don’t fit together. They can never mate in the wild and are so considered different species.
* Breeding habbits: Some animals can produce fertile offspring, but their mating rituals differ so much that they will never mate on their own naturally.
I think you should see a pattern here. The fact that they *could* in theory produce fertile offspring isn’t as important as if they naturally do so. If their gene pools aren’t mixing naturally, most scientist would argue they shouldn’t be considered the same species. You could make the argument that neanderthals were the same species as early humans, but you could also make the argument they were not. They had such significantly different traits than us that it generally makes more sense to talk about them as a different species. Our gene pools did mix a bit, apparently not to a great extent. Otherwise we would have more or less the same traits.
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