Board Thread:Lore Discussion/@comment-9062114-20140323022721/@comment-17114085-20140323023814

I personally believe that Men and Mer are members of the same species, being sub-species. And that Khajiit and another species that derived from the Mer sub-species. That explains why Mer and Men can interbreed. And why Khajiit can only interbreed with Mer. I've heard that Khajiit are sometimes called the Moon changed Elves or something like that, can't remember the actual comparison.

As for argonians, they are reptiles while the other races are mammals. So they aren't the same species as the other races.