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A couple commenters have made reference to evolutionary biology and “human nature” as the causal force behind existing ethical systems. Now, there’s obviously something to that (look for an upcoming post on something called the Darwinian Dilemma), but it also means that the time has come for us to draw an important distinction: most humans are persons, and as far as we know all persons are humans, but that does not mean that the definition of one exhausts the definition of the other.
“Human” is a label referring to a set of biological characteristics. Personhood is … something else harder to define. But, with the help of some examples, I think it is doable. So: I would argue that an individual who no longer has any brain function beyond basic life support is a human that is no longer a person. On the other hand, to use several geeky examples, Kal-El (pictured), Frodo Baggins, Data from The Next Generation and Dogbert are all non-human persons. Recently, some scientists have argued that the same applies to dolphins.
So what, then, is a person? I think the existentialist definition works best: Heidegger and Sartre refer to man as the “being-for-itself” (in Sartre’s French, the pour sois). What this means is that persons are the only things in the universe that can reflect on themselves and their own actions. The other way to put this is that persons are defined by the fact that they alone are self-aware.
This is an important distinction to make because I think a good ethical system is one which seeks to describe good interactions between persons. So, for example, murdering Frodo in order to get your hands on the one ring is unethical, whereas killing a non-person animal for food or terminating life support for someone in a persistent vegetative state at the wishes of the family is not necessarily wrong in and of itself.