When I discuss the scientific study of human consciousness with my general-education students, I begin by introducing them to a field-monitoring device used by a colleague in Environmental Studies. It stands three feet high and continually records temperature, relative humidity, precipitation, barometric pressure, wind speed and direction, and sun intensity. I ask my students, when it’s raining, does this device know it’s raining? Quickly they recognize that it doesn’t. So, I continue, how could you modify it so that it does know when it’s raining? Not just modify it so that it responds, zombie-like, to the rain—by putting on a hat, say—but so that it is conscious of the rain?

For this question they have no answer, and with good reason. This is known in consciousness studies as “the hard problem.” How can matter be put together in such a way that it can become conscious of the world? Philosophers have long asked this question, and in recent years it has been undertaken by biologists as well. The biologists fall into the materialist camp—those who believe, as the evolutionary psychologist Nicholas Humphrey does, that “nothing interesting occurs without a material cause.” Some philosophers are in the materialist camp with them, but others are dualists, who believe that mind and brain are not the same thing and that no material explanation of mind is possible. Still others are mysterians, who believe that consciousness will always remain a mystery beyond our power to say whether it is or isn’t material.

In Soul Dust: The Magic of Consciousness, Humphrey proposes an answer to the hard problem, but his main concern lies with a related question: Why did consciousness evolve? To most of us, the advantages of consciousness seem so obvious that the question need hardly be asked, but to many who have thought about consciousness the most, the question is more difficult than it first appears. Might we not, they ask, take in the data of the world and respond to it without actually being conscious—like the zombie device standing out in the field? Recent studies, after all, have shown that we respond to stimuli faster than it can register in our consciousness—that it only seems that our responses are the product of our conscious powers. The philosopher and cognitive scientist Jerry Fodor has put it this way: “As far as anyone knows, anything that our conscious minds can do they could do just as well if they weren’t conscious. Why then did God bother to make consciousness?”

Humphrey embraces the question (though he substitutes “natural selection” for Fodor’s “God”), but asserts that scientists and philosophers have taken the wrong approach to answering it. Repeatedly, he points out, these thinkers inquire into what consciousness enables in us. If wings allow birds to fly, and language allows humans to communicate, what does consciousness make possible? Humphrey argues that this is the wrong question. Consciousness in his view does not enable us to do something, but rather gives us something—namely, a greater desire to live than we would have if we were non-conscious. Because we are conscious, we enjoy the world, we give value to the things of the world, and we set goals for ourselves to further our enjoyment and enhance the meanings we give to things. Herein, Humphrey argues, lies the Darwinian explanation that science demands. Consciousness gives us an advantage in the struggle for survival because conscious beings, in contrast to those hypothetical zombies, want life more. And wanting life more equips us to outcompete the nonconscious zombies in the struggle for survival, and thus to be more successful in passing on our genes.

This argument, the heart of Soul Dust, is developed in the book’s middle chapters, and these chapters will be of the most interest to the general reader. Humphrey has read widely not just in philosophy and the sciences, but in the arts and humanities as well. In presenting the fullness of human life made possible by human consciousness, he quotes incisively from artists and poets ranging from Elizabeth Barrett Browning and A. A. Milne to Wassily Kandinsky and Woody Allen. By drawing on sources outside the usual purview of scientific or even philosophical discussions of consciousness, Humphrey presents a richer understanding of what it means to be human than do most writers in the field, and we owe him a debt of gratitude for that.

Nevertheless, by keeping human consciousness enclosed within the Darwinian insistence that all signature aspects of humanity must have evolved in order to make the species more reproductively fit, Soul Dust becomes both reductive and repetitive. For instance, to illustrate our human enjoyment of life and our capacity for wonder, Humphrey quotes the familiar lines of Gerard Manley Hopkins:

Glory be to God for dappled things—

For skies of couple-colour as a brinded cow;

For rose-moles all in stipple upon trout that swim;

Fresh-firecoal chestnut-falls; finches’ wings.

How disappointing, then, to have Humphrey describe this wonder and enjoyment as a mere tool we use to outcompete hypothetical zombies in reproducing our genes. All these dappled things, Soul Dust declares, are not real—much less the glories of God—but merely creations of our minds. When he quotes Vincent van Gogh’s ecstatic description of nature’s extraordinary beauty, Humphrey does so only to illustrate the “category mistake” we all repeatedly make in attributing the qualities we see to things in the world. “The impression you get that the qualities inhere in the things as such,” he declares, “is all part of the illusion.”

Yes, humans inhabit “an enchanted world,” a world that fills us with awe, but it is an enchantment wholly of our mind’s making. And this, for Humphrey, is the key to consciousness. “We need to establish what, if any, is the biological advantage of being awestruck,” he writes. Would living in the dreary, unenchanted world of a zombie make us “less successful” as a species? Time and again, Humphrey returns to this reductive question, and always with the same result: our extraordinary consciousness has been produced by natural selection because those creatures possessing it have an enhanced will to live and thus an increased shot at passing on their genes. What a paltry thing this consciousness is, no matter how much exuberance Humphrey brings to describing it.

Is consciousness really just a creator of entertaining illusions, a device to trick us into being more avid biologically? Will this be the best explanation that evolutionary science can propose? That seems unlikely. Such a remarkable adaptation deployed only for advantage in passing on genes is rather a bit of overkill, after all. Of the 665 billion tons of biomass on earth, well over 99 percent consists of plants and bacteria quite successfully passing on their genes with no consciousness at all. Even in the animal kingdom, consciousness is a marginal attribute. The number of ants on earth is estimated to be somewhere on the order of 50 billion billion. Humans, by contrast, number only about 7 billion. At best, consciousness may have enabled animal life forms to achieve larger sizes, but even this is counter-productive, as increased size is accompanied by decreased numbers and thus fewer passed-on genes. Antarctic krill, which grow to about two and half inches and live in dense swarms of up to thirty thousand per cubic meter, outnumber the whales that eat them by trillions to one, though consciousness is unnecessary to their success in passing on their genes.

But perhaps this is the wrong way of assessing consciousness and its uses. After all, the function of consciousness, especially human consciousness, has been discussed for many centuries, and much of this discussion has anticipated the blind alley that a humanistic Darwinian such as Humphrey finds himself going down. Perhaps consciousness, with its accompanying joy and wonder, might better be understood not as a tool of evolution, but as evolution’s gift. We do not yet know by what means evolution has given us this gift, much less how it can exist at all in a physical universe. Human consciousness may even turn out to be what Stephen Jay Gould and Richard Lewontin termed a “spandrel,” a side product of evolution that doesn’t itself bestow evolutionary advantages. But we can know what consciousness makes possible for us. It makes us capable not just of being biologically alive, but of being what St. Irenaeus in the second century called homo vivens, human individuals fully alive—and not to illusions, but to the real dappled world of Gerard Manley Hopkins and to the God Hopkins credits for that world’s existence. Soul Dust, whether Humphrey means it to or not, takes Darwinian thought a step closer to this old truth.