Traditional morality assumes that there is something morally special about being human. The fact that someone is a human being, rather than, say, a dog or a cow, makes a big difference in how he or she may be treated. Humans have full and equal moral worth or dignity and thus may not be killed, even if doing so would promote the greater good, whereas non-human animals have a lesser moral status and can be sacrificed for even the most trivial human pleasures.
This moral worldview fits well with the Aristotelian idea of a hierarchy of being, according to which each species is a static group of organisms with a distinct essence. The philosophical line that morally distinguishes humans from other animals corresponds to the empirical line that Aristotle thought distinguishes the human species from other animal species. Since the publication of Charles Darwin’s The Origin of Species in 1859, however, we know that there is no such line on the empirical side of things. We now understand that all life is interrelated, and that biological characteristics come in degrees and continually evolve as a result of natural selection. As the principle of evolutionary continuity informs us, any differences between species are differences in degree, and not in kind. The real picture looks something like this:
According to traditional morality, a small number of individuals in this diagram, us, have a special moral status, and form the community of moral equals, from which all non-human life is excluded. If that is to be true, we should be able to draw a line between us and them:
But where should we draw that line? There is no recognizable discontinuity in the spectra of degrees of capacity (or potential) for the psychological capacities that are commonly associated with the special moral status of humans. Being autonomous, rational, self-conscious, able to use language, and so on all are so-called scalar properties, i.e., they come in degrees, which makes line-drawing problematic, for at least two reasons:
- Wherever we choose to draw the line, our choice will be arbitrary, at least to some degree.
- Even if we somehow find a non-arbitrary way to draw the line, doing so implausibly opens a moral gulf between individuals whose difference from one another in terms of empirical reality is entirely unremarkable.
To further illustrate this point, let us borrow a thought experiment from English evolutionary biologist Richard Dawkins:
Find a picture of yourself. Now take a picture of your father and place it on top. Then find a picture of his father, your grandfather. Then place on top of that a picture of your grandfather’s father, your great-grandfather. […] Now do the same thing with his father, your great-great-grandfather. And just carry on piling the pictures on top of each other, going back through more and more and more great-great-greats. […] How many greats do we need for our thought experiment? Oh, a mere 185 million or so will do nicely! […] It isn’t easy to imagine a pile of 185 million pictures. How high would it be? Well, if each picture was printed as a normal picture postcard, 185 million pictures would form a tower about 220,000 feet high: that’s more than 180 New York skyscrapers standing on top of each other. […] What did [your 185-million-greats-grandfather] look like? An old man with wispy hair and white side-whiskers? A caveman in a leopard skin? Forget any such thought. […] Your 185-million-greats-grandfather was a fish. So was your 185-million-greats-grandmother, which is just as well or they couldn’t have mated with each other and you wouldn’t be here.Richard Dawkins, The Illustrated Magic of Reality (Simon and Schuster, 2012), pp. 38-40
If traditional morality is to be believed and there is to be a community of moral equals, one of your great-great-greats must have been the first to be a member of that community. Let us call him Adam. Which picture in the pile shows Adam? It is hard to tell! In fact, there seems to be no principled way to determine who among your ancestors was Adam. This is not an innocuous case of vagueness, as in the case of the concept of baldness, but a serious shortcoming, as much depends, in terms of morality, on where we draw the line that separates equals from unequals. It makes a great difference in the way your (great)n+1-grandfather would have deserved to be treated whether we decide that he is Adam, or instead decide that your (great)n-grandfather gets to be Adam, and yet there seems to be no more or less reason to go one way rather than the other. For example, who among the two gets to be Adam matters greatly for the morality of killing them. It is much more seriously wrong to kill someone with full moral status than it is to kill someone with a lesser moral status, and it is implausible, and moreover morally unacceptable, that there could be individuals for whom it depends on an arbitrary, unprincipled choice whether they are entitled to the protection enjoyed by moral equals.
Further, whichever picture we pick, the intrinsic difference between the individual on that picture, Adam, and his father will be unnoticeable. If the two of them were to stand in front of us, we would most likely not be able to tell who among them is more similar to us in terms of autonomy, rationality, self-consciousness, language ability, and all the other capacities we commonly associate with our heightened moral status. In stark contrast to whatever minor differences in biological reality there may be, the way traditional morality would have us treat Adam, who has full moral status, is radically different from the way he would have us treat his father, who does not have full moral status. That is implausible. It is implausible that a small difference in genetics or capacity makes a momentous difference in terms of moral status.
What follows from all this? Traditional morality seems to be in serious trouble. It does not fit our modern scientific view of the natural world. The line posited by traditional morality, between humans and other animals, is a remnant of an obsolete moral outlook, not least because it has no counterpart in empirical reality. It is time to look for tenable alternatives. In a new paper, “Are humans more equal than other animals? An evolutionary argument against exclusively human dignity,” forthcoming in Philosophia, I hint at one such alternative, after providing a more detailed version of the argument sketched in this blog post. You might also want to have a look at an article I wrote on a closely related topic, “Mental-Threshold Egalitarianism: How Not to Ground Full Moral Status,” published in Social Theory and Practice, and my dissertation.