The problem here is that you are assuming there is such a thing as 'essence', that living organisms have an 'essence', a 'who/what they really are', that they are 'things an sich'. As the history of Western philosophy shows, this 'essence' is a difficult thing to pinpoint or define. Like I said above, this is a tricky issue, as it assumes man has 'essence'. An alternative is to think in terms of 'who can get along with whom, and with whom not'. Say, if I see someone dressed as a hippie or a beatnik, or an Aboriginal, or an Ayn Rand fan it means that I will not get along with such a person. I predict that the quality of any relationship I might have with them will be bad or insignificant to me. So instead of thinking in terms of 'essence', it is possible to think in terms of 'predicted quality of interaction'. This seems rather accurate and seems to be a good guideline for action that is satisfactory to the individual pursuing it. However, this alternative is, of course, not politically correct or 'humanistic' etc.