"There is no immutable, clearly defined ‘essence’ that characterizes human beings, and only them, within the whole animal world."
My book, Saving Gaia, refutes this. The subtitle is "Rational Darwinism." More emphasis should be given to the long geologic time periods humans spent as canopy dwellers from the Miocene Epoch on to the recent. We are close to the orang and gibbon in sentiment. We love being near or in arboreal settings. Humans didn't become omnivores until Ardipithicus descended from the trees around five million years ago.
We are much more comfortable and at home in a tree house than we are in a massive skyscraper. Wood and leaves are closer to our DNA than glass, aluminum and concrete big cities. Our artists and poets point this out. Check out Allan Ginsberg's "Howl.'

[lulu.com]

I don't think there can be a single "ONE" unified theory of human nature.

This is really confusing. What does Aristotle have to do with evolution, biology, or science for that matter? He had no concept of these thing, because they did not exist in his time. What is 'essence, I'm confused on that topic.