As a teenager growing up in the rural American Midwest, I played in a Christian rock band. We wrote worship songs, with texts on religious themes, and experienced the jubilation and transport of the music as a visitation by the Holy Spirit. Then one day, as my faith was beginning to waiver, I wrote a song with an explicitly nonreligious theme. To my surprise I discovered that when I performed it, I was overcome by the same feelings, and it dawned on me that maybe what we had experienced all along was our own spirits, that what had called to us was the power of music itself.
In truth, I wasn't thinking through much at the time. Later, as a graduate student of philosophy, I did start to think a lot about science and ethics, and I began to undergo a parallel shift of outlook. Having embraced a thoroughly naturalistic, materialistic worldview, I wondered: If everything is just matter, how could anything really matter? How could values be among the objective furniture of the universe? It is not as if anyone expected physicists to discover, alongside electrons, protons, and neutrons, a new fundamental moral particle--the moron?--which would show up in high magnitudes whenever people did nice things.
Then there was J. L. Mackie's famous argument from "queerness": objective values would have to be such that merely coming to appreciate them would motivate you to pursue them. But given everything we know about how ordinary natural facts behave (they seem to ask nothing of us), how could there possibly be states of affairs with this strange to-be-pursuedness built into them, and how could we come to appreciate them?
At the same time, I was taken in by the promises found in some early sociobiology that a new evolutionary science of human nature would supplant empty talk about objective values. As Michael Ruse once put it, "morality is just an aid to survival and reproduction," and so "any deeper meaning is illusory." Niceness may seem self-evidently right to us, but things could easily have been the other way around, had nastiness paid off more often for our ancestors.
I have since been convinced that I was looking at all of this in the wrong way. Not only are values a part of nature; we couldn't avoid them if we tried.
There is no doubt that had we evolved differently, we would value different things. However, that alone does not show that values are subjective. After all, hearing is accomplished by psychological mechanisms that evolved under natural selection. But it does not follow that the things we hear are any less real. Rather, the reality of the things around us helps to explain why we have the faculty to detect them. The evolved can put us in touch with the objective.
In fact, we are all intimately familiar with entities which are such that to recognize them is to be moved by them. We call them reasons, where a reason is just a consideration that weighs in favor of an action or belief. As separate lines of research by psychologist Daniel Wegner and psychiatrist George Ainslie (as synthesized and interpreted by Daniel Dennett) strongly suggest, our reasons aren't all "in the head," and we cannot help but heed their call.
At some point in our evolution, the behavioral repertoire of our ancestors became complex enough to involve the review and evaluation of numerous possible courses of action and the formation of intentions on the basis of their projected outcomes. In a word, we got options. However, as an ultrasocial species, for whom survival and reproduction depended on close coordination of behaviors over time, we needed to manage these options in a way that could be communicated to our neighbors. That supervisor and communicator of our mental economy is the self, the more-or-less stable "I" that persists through time and feels like it is the author of action. After all, if you want to be able to make reliable threats or credible promises, you need to keep track of who you are, were, and will be. According to this perspective, reasons are a human organism's way of taking responsibility for some of the happenings in its body and environment. As such, they are inherently public and shareable. Reasons are biological adaptations, every bit as real as our hands, eyes, and ears.
I do not expect (and we do not need) a "science of good and evil." However, scientific evidence can show how it is that things matter objectively. I cannot doubt the power of reasons without presupposing the power of reasons (for doubting). That cannot be said for the power of the Holy Spirit.