The "we are nothing but" claim takes countless forms and comes at us from many sides. To cite just a few famous cases:
"You," your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells and their associated molecules. As Lewis Carroll's Alice might have phrased it: "You're nothing but a pack of neurons." (Francis Crick)
There is no spirit-driven life force, no throbbing, heaving, pullulating, protoplasmic, mystic jelly. Life is just bytes and bytes and bytes or digital information. (Richard Dawkins)
Man has to understand that he is a mere accident. (Jacques Monod)
People, after all, are just extremely complicated machines. (E. O. Wilson)
I have a working hypothesis. Leaving Brooks (about whom I know almost nothing personal) aside and focusing instead on the wider rhetorical phenomenon: Why do we so often encounter today the assaultive reductionist assertions, "the human being is only ...," "we are nothing more than ...," "we are merely ..."? The vacuity of the claims together with the characteristic aggressiveness of the authors certainly raises some interesting questions.
We get a hint of what is going on by considering the negative and belittling cast of the assertions. Clearly the authors, consciously or unconsciously, see themselves as bringing us down a peg or two. They could, after all, have reveled in the glories and depths and wisdom of the natural world revealed by science. But, no, they want to make sure we understand that, as products of this world, we are only such-and-such. Apparently their own pessimistic sense of the matter is that we are discovering the human reality to be an impoverished one a reduced one, in fact this despite the usual explicit statements about what a stunningly rich and profound world science presents us with.
We may wonder, then, what is behind this sense of being reduced. Whence arises this feeling of inferiority requiring the use of pejorative and reductive language? My own suspicion is that one of the most fundamental insights of Carl Jung may throw light on the matter. The Swiss psychiatrist pointed out that when integral contents of the personality are lost to consciousness, an inferiority results. Moreover, the sense of inferiority gives rise to moral resentment and "always indicates that the missing element is something which, to judge by this feeling about it, really ought not to be missing, or which could be made conscious if only one took sufficient trouble" (Jung 1972, pp. 139ff.).
I feel free to mention this only because the way a personal lack leads to a sense of inferiority and then to moral resentment (so that we are happy to bring others down a peg or two, to our own level) is such a universal fact of life that none of us if we possess the slightest self-awareness can fail to recognize the process in our own lives. So it is not a matter of pointing fingers at individuals or singling out any group as "morally challenged." But where we can recognize a broad social and intellectual pattern such as the one presented by reductionist rhetoric, we really ought to try to understand what is going on.
The lack Jung spoke of was a loss of contents properly belonging to consciousness. Where do we see such a loss more in evidence than in disciplines such as artificial intelligence, cognitive science, and reductionist science in general? Surely if there is any place where we should expect a loss of conscious contents, it is where such contents are commonly denigrated as a matter of principle. The main drift in these fields is to ignore as completely as possible the immediate contents of consciousness, reinterpreting them in terms of what is not conscious. It is hard to imagine a more direct route to the conditions of lack, inferiority, and moral resentment Jung describes. The entire project of these disciplines is to drop things from consciousness.
In other words, there is a truth of sorts in the reductionist claims. Or, you could say, there is truth in the plight of the reductionist. At the level of its symptoms the psyche never lies. A kind of practical reductionism really has been occurring as the inevitable result, over time, of theoretical reductionism, and we should not be surprised if it produces pathological results. In a society where the cry echoes from all sides, "You are nothing but a machine," we can rightly ask whether what we are really hearing is, "I sense that I am becoming nothing but a machine and, dammit all, I won't tolerate anyone else being more than I am."
There is in this symptom, as Jung clarifies it, a paradoxical double aspect: on the one hand, a sense of inferiority, but, on the other hand, a compensating "psychic inflation" through which the ego assumes god-like pretensions. After all, am I, as one of the cognoscenti, not in the omniscient position of knowing the real truth about everyone else, while they remain benighted and self-deluded, ignorant of their "mereness"? We may wonder as well whether this tendency toward inflation helps to explain grandiose visions of our future as a race of cyborgs destined to become masters of the universe.
Another consequence of the loss of conscious contents, aside from a sense of inferiority and a compensating ego inflation, is that our conceptual resources for understanding the world are diminished. When we lose awareness of all but the machine-like in ourselves, we also lose the ability to conceive the world as anything but a machine. Those whose intellectual horizons are encompassed by digital machinery tend to see the world computationally, just as their predecessors saw the world in terms of clocks, cameras, steam engines, telegraph lines, and movie projectors. There is security in believing the world is like the things one knows best, and intellectual ease in draping one's well-practiced ideas like a veil over the Great Unknown.