It is a cherished belief of most people that human beings simply as such have equal value and rights and that they have significantly greater value than animals. However, this claim is difficult if not impossible to justify given a naturalist worldview. For many naturalists, the best, perhaps only, way to justify the belief that all humans have equal and unique value simply as such is in light of the metaphysical grounding of the Judeo-Christian doctrine of the image of God. Such a view depicts humans as substances (a particular thing like a dog that is a simple, indivisible unity of parts and attributes at a time, that remains the same through change, and that has a nature (being a human, being a carbon atom, being a dog) that provides an answer to the question “What kind of thing is this particular object?”) with a human nature, and for at least two reasons, naturalists claim that this framework must be abandoned.
For one thing, the progress of science has regularly shifted entities (e.g., heat) from the category of substance (heat was once viewed as the substance caloric that flowed into or out of objects) to the category of quality (heat is an attribute of warmth, not a thing like caloric), or quantity (heat is not the attribute of being warm, it is the mathematical quantity of mean kinetic energy). Since natures are the essences of substances, if there really are no substances (and, instead, there are just collections or aggregates of atoms and molecules), then we should reject the existence of natures. Thus, there most likely is no such thing as a human nature, and talk of such should be understood solely within the categories of biology, chemistry, and physics and with a view of humans as mere ordered aggregates of parts.
Second, Darwin’s theory of evolution has made belief in human nature, though logically possible, nevertheless, quite implausible. As E. Mayr has said:
The concepts of unchanging essences and of complete discontinuities between every eidos (type) and all others make genuine evolutionary thinking impossible. I agree with those who claim that the essentialist philosophies of Aristotle and Plato are incompatible with evolutionary thinking.
This belief has, in turn, lead thinkers like David Hull to make the following observation:
The implications of moving species from the metaphysical category that can appropriately be characterized in terms of “natures” to a category for which such characterizations are inappropriate are extensive and fundamental. If species evolve in anything like the way that Darwin thought they did, then they cannot possibly have the sort of natures that traditional philosophers claimed they did. If species in general lack natures, then so does Homo sapiens as a biological species. If Homo sapiens lacks a nature, then no reference to biology can be made to support one’s claims about “human nature.” Perhaps all people are persons,” share the same “personhood,” etc., but such claims must be explicated and defended with no reference to biology. Because so many moral, ethical, and political theories depend on some notion or other of human nature, Darwin’s theory brought into question all these theories. The implications are not entailments. One can always dissociate “Homo sapiens” from “human being,” but the result is a much less plausible position.
Finally, this observation has lead a number of thinkers to claim that the traditional sanctity-of-life view of human beings is guilty of speciesism (a racist, unjustified bias towards one’s own biological classification) and to settle on personhood, and not simply on being human, as constituting our locus of value. Thus, value resides in personhood, not humanness. What is a person? A person is anything that satisfies the right list of criteria, e.g., has a self concept, can form meaningful relations with God or others, can use language, can formulate goals and plans, etc.
There are two key implications of this view: 1) There can be human non-persons (e.g., defective newborns, people in comas) and personal non-humans (e.g., orangutans) and the latter have more value than the former. 2) Since the features that constitute personhood can be possessed to a greater or lesser degree, then some individuals can be more of a person and, thus, have more rights and value than other individuals. In my view, 1) is false. Being a person is to being a human as being a color is to being red. There can be non-human persons (angels) but there can be no human non-persons just as there can be colored non-red things (blue things) but no red non-colored things. Proposition 2) is one that naturalists have worked hard, and in my view, unsuccessfully, to avoid. In any case, it should be clear that the high intrinsic and equal value of all human beings is easy to justify given Christian theism, but they are hard to square with naturalism.
One day my daughter, Ashley, came home from sixth grade with a Martin Luther King, Jr. flier that said “All human beings should have equal rights and be treated as having equal value.” I asked her if she believed this statement, and when she answered in the affirmative, I asked her why. Thinking she could get rid of me by giving an answer I wanted, she said it was because of God.
I responded by inviting her to pretend that there was no God. I pointed to a beautiful painting on the wall over our sofa and to a piece of trash on the coffee table I forgot to throw away the night before. I then asked that if the house were burning down and she could save only one of these objects, would she be obligated to save one, or would the two objects be on a par so she could decide which to save by flipping a coin. She responded that the painting should be saved because it was of more value than the trash. I asked the same question about the piece of trash and our dog, KC. Irritated, she affirmed that the dog should be saved, not the trash, because KC is precious.
I then pointed out that we had learned a lesson: Equals ought to be treated equally, and unequals ought to be treated unequally. It would be wrong to flip a coin to decide between the trash and our dog, because that would be to treat two unequal things as though they were of equal value. I then noted that human beings have nothing in common that is equal: some are beautiful, some ugly, some smart, some not, some athletic, some not, some socially useful, some not, and so on. Ashley responded by pointing out that there was, in fact, something we all have in common: belly buttons.
I then noted that some have large and some have small belly buttons. “Should the people with large ones be given greater rights?” I asked. Moreover, if it were in virtue of having a belly button that we had value, if we removed someone’s belly button, could we now use that person as a door stop (since he/she had lost his/her source of value)?
I concluded that if equal rights and value were to be justified, two things were required: (1) We had to have something in common that was equal. (2) Whatever that “something” was, it had to be deep, weighty and important, not silly and trivial like a belly button. If we are made in the image of God as Dr. King argued, then equal rights/value is easy to justify. If not, it may well be impossible to justify. That’s something to ponder, isn’t it?