In comments to this post, Gaius asked some incisive questions about how a theist who accepts the general evolutionary picture of the world can avoid falling back on some form of divine command theory (also known as theological voluntarism).
The problem arises because, post-Darwin, it’s difficult to attribute inherent purposive-ness to natural processes. But the old natural law ethics, which has probably been the chief alternative to divine command ethics in Christian history, rested on a teleological view of nature that no longer seems tenable: the good life consisted in realizing one’s essential nature.
Maybe it’s my Platonistic inclinations, but I’ve never been particularly happy with this choice. I think a full understanding of value will inevitably make reference to the divine, but I don’t think moral rules are simply the arbitrary dictates of God. They are, I believe, rooted in the nature of things, but not properly accounted for by the “biologism” of some versions of natural law.
My general view is that each individual creature is an expression of (or resembles, or participates in) the divine. The Catholic theologian Denis Edwards, following St. Bonaventure, puts it like this:
In the life of the Trinity, everything flows from the fecundity of the Source of All, whom Bonaventure calls the Fountain Fullness (fontalis plenitude). He sees the eternal Word of Wisdom of God as the Exemplar, the image of Fountain Fullness. When God freely chooses to create, the fruitfulness of Trinitarian life finds wonderful expression in the diversity of creatures. Each different kind of creature is a reflection and image of the eternal Word. (Denis Edwards, Ecology at the Heart of Faith, p. 71)
Creation, we can say, is a form of God’s self-expression. Thus, each creature, because it reflects the divine, has inherent value. Further, at least some of these creatures—human beings and many other animals—have an experiential welfare, or, to put it another way, their lives can go better or worse for them. And because these creatures have inherent value (being a reflection of the divine), their well-being matters, not just from their own point of view, but from a universal, or impartial, point of view.
It’s clearly a matter of controversy what constitutes a good human life—that is, what it means for a human life to go better or worse for the one living it. But there do seem to be some universals. Pleasure, happiness, knowledge, freedom, and companionship seem to be among the goods universally prized by human beings. Likewise, all humans seek, other things being equal, to avoid pain, suffering, frustration, ignorance, bondage, and enmity. (A modified, though not wholly dissimilar, list could be provided for other animals.)
So, it’s not merely a matter of God’s preference or whim that, say, happiness is preferable to misery. This is a fact rooted in the constitution of the world (which, of course, theists believe is ultimately traceable back to God). And for Christians at least, ultimate happiness consists in greater knowledge of and union with God or the Good. Nothing less will truly satisfy us (and this fulfillment only comes to complete fruition in the life to come).
While this general picture makes reference to the nature of things, note that we’re not talking about “reading value off of biological processes” here. Clearly the kinds of goods that contribute to a human animal’s well-being are rooted in our biology, but biological processes as such don’t have the same status in this account as they do in some versions of natural law ethics. To take an obvious example, most of us no longer regard it as wrong per se to interfere with the process by which intercourse (sometimes) leads to conception. We need an independent moral criterion to decide when that may or may not be a good idea. And this will involve reference to the kinds of goods that make for a well-lived human life.