You can make up stuff if you want, but it is a fiction.Suppose that in some hidden corner of the Earth we would discover a bunch of sapient Neanderthals, who are perfectly able to further their own species, but are unable to mate with the Homo Sapiens. Would they be considered “fully humans”?
Or due some radioactive radiation a group of people would develop some mutations, which would allow them to communicate telepathically, but would not be able to interbreed with “regular” humans? What about those hypothetical beings?
Laws are not based on fiction.