Man’s being an unfinished, defective animal has been the root of his uniqueness and creativeness. He is the only animal not satisfied with being what he is. His ideal was a combination of the perfections he saw in the animals around him. His art, dances, songs, rituals and inventions were born of his groping to compensate himself for what he lacked as an animal. His spirituality had its inception not in a craving to overcome his animality but in a striving to become a superior animal.
–Eric Hoffer, First Things, Last Things (1971), p. 11
This view is historical and anthropological, but is totally contrary to the notion of spirituality developed in the Axial Age, for example in Christianity. Assuming a basic animality and seeking to transcend it is the contrary notion. Transcending a natural animality would be absurd, however, without the idea that the animalistic condition were due to some kind of mistake.
So, the origin of our animalistic nature has to be in a historical event, a confluence of circumstance and autonomous will, which a Christian theologian would call “The Fall.” That leaves room for a pre-existing ideal instantiation of human existence, when circumstances were unpolluted and will was trusted. Spirituality then becomes not a path to more animalistic powers, the expression of will to control circumstance, but rather a path to transcend circumstance and will.*
If a human could have an essentially animal nature, then he would actually be an animal, and have no desire to be other than what he is. Even becoming more than what he is at the moment would be simply a fuller expression of what he could be, which would still be the same animal, but better. To the extent that he might seem to be a different animal, that would be a superficial difference, a matter of morphology or behavior.
Another possibility would be that the progeny of an individual human animal could become a different kind of human animal; that is, it could “evolve.” That doesn’t concern the particular individual in question, though, unless the individual in question has some abstract notion of humanity which extends beyond his own existence. Having such an notion would mean that individual is not an animal, which has no desire to be other than what he is, and so does not imagine himself being part of an abstract taxonomy or progression. That individual is instead a human which, having no notion of magically acquiring new powers in itself, imagines a spiritual connection to other individuals which might have different powers.
*”Circumstance” means everything given, including environment and the body. “Spirituality” means any desire to be other than what we seem to be. “Will” means the individual intent.