What do you think about the nature of man?

I think you have an interesting theory, but if man is not always rational, then how can we conclude that man's true nature possesses a rational nature? Do not other mammals know when to eat, when to sleep, when to fight back, and when to be afraid? Is that not also a faculty of reason? If not, and you believe it is just natural instinct, then are you assuming that animals have no free will, and are blindly choosing to believe everything their instincts tell them to do. If this is the case, then how do we know for sure that animals don't have a faculty of reason and don't think for themselves? Isn't it possible that, because we are not them, that they do possess a faculty of reason, and a form of free will, that we are not aware of?