Now, if the argument is simply that, because we evolved from bacteria, we have no more moral worth than they do, it is obviously a non-sequitur. It’s the same as if one claimed that because Adam was made from the dust of the ground, he has no more value than that dust – or that Eve is at best worth one lousy rib. However, those who make the above argument are likely to insist that evolution presents us with something different: It’s not merely that we came from bacteria, it’s that we are “just like bacteria” in certain important respects. Adam was endowed with a soul, whereas the descendants of bacteria presumably are not.
But what is it about the soul that’s supposed to make a difference? Two possibilities come to mind. First, a soul is non-physical, whereas if naturalism is true, we are purely physical beings. Second, a soul is supposedly immortal. Let’s consider each one of these in turn.
Does being made of matter make one morally insignificant? I don’t see why it should. For suppose that what naturalism says is true, so that we humans, with our consciousness, our feelings, our desires, and so on, are no more than complex arrangements of matter. The fact remains that we are conscious, that we have hopes and dreams, that we care about others – in other words, that most of what we take to be important in our lives remains. What difference can it make, then, whether the ultimate substance that makes this possible is material or immaterial? And what’s so special about non-physical “stuff” anyway?
What about being immortal? If naturalism is true, then presumably our lives are finite. But does that mean that therefore it doesn’t matter what happens to any of us? That it is therefore okay to, say, torture innocent people to death? I doubt even the strongest critic of naturalism really believes such a thing. At any rate, how would immortality change anything? If life is worthwhile, that is because the temporal spans that it is made of are themselves, on the whole, worthwhile. And if so, then that’s true whether or not life continues indefinitely.
The fact that we evolved from bacteria does not mean we are “just like bacteria”. There are characteristics that we possess which bacteria lack – and those make us morally different from bacteria.