Human is an intelligent specie originated from Africa, Earth. That's it. Not being able to give a definition does not mean, that reality is undefined. It just means that you are stupid.
And why the Hell demons can't lie, when they are literally a combination of human and butthurt? Maybe they can't drink or swear as well? If that's the case, then they have a great parenting potential. They are a new stage of "evolution" of humanity, but in a different way, to what Akira had himself imagine.