Why Does Consciousness Exist?
I mean this question to be a question of biology: what adaptive purpose was served by the evolution of consciousness? Consciousness, like other biological traits, evolved because it contributed to the survival of the organisms that possess it, so there must be an answer to the question of what its survival value is. That is, consciousness has various distinctive properties and among them are properties that aid the survival of the organism (ultimately the genes): what are these properties? We might mention subjectivity and privacy—how do these contribute to survival? No answer suggests itself: would consciousness be less adaptive if it were objective and public? Why does it help a conscious state to perform a vital function that it can’t be known by others or can only be grasped from a particular point of view? So there must be another property or set of properties (perhaps less salient) that perform the necessary adaptive work. There must be something about consciousness that makes it a worthwhile addition to an organism’s survival equipment.
One feature of consciousness is familiar from the tradition: it is known about in a peculiarly intimate way. Consciousness is both self-intimating and infallibly known: it reliably informs us of what is going on within it, and when we form beliefs about it we are invariably correct.  Let us say that it possesses the property of epistemic privilege—it is closely hooked into our epistemic faculties. For example, if you feel hungry, you know you feel hungry; and if you think you feel hungry, you do feel hungry. As it is sometimes put, consciousness is transparent—it is available to knowledge in a special way. Is this a happy accident of no biological significance or is it something that plays a vital role in the life of the organism? It may seem like a pointless luxury: the organism gets to know about its states of consciousness quickly and easily—nice for the self-centered organism, perhaps, but where is the biological payoff? The organism feels hunger pangs and immediately knows it—hunger qualia convey their existence swiftly to the organism’s cognitive system. It knows it feels hungry, that its consciousness is active in the hunger department: but this is not all it knows–for if it feels hungry, there is a very good chance that it actually needs food. There is lawful connection between needing food and feeling hungry: the latter strongly indicates the former. So the organism knows it needs food by knowing that it feels hungry. Knowing this it sets about getting food (other things being equal). It’s obviously good for the organism to know it needs food when it does, and the conscious state of hunger clues the organism in to when its food resources are depleted. So there is a two-stage process here: lack of food triggers conscious feelings of hunger, and feelings of hunger trigger knowledge of lack of food via knowledge of the accompanying feelings. If you were designing a functioning organism that is constantly faced with food shortages, it would be sensible to build in a mechanism that generates the necessary knowledge in a reliable manner. The feeling itself does not have the same functional characteristics as the knowledge that results from it, so the knowledge adds something to the organism’s biological resources. Given that such knowledge is desirable, and given that consciousness plays a role in producing it, we begin to see why consciousness might perform a useful biological function. It helps in the task of preserving the organism by informing it of what is going on in its body in respect of food. Obviously the same story could be told about feelings of thirst and dehydration, or about feelings of pain and bodily damage. These kinds of consciousness play the role of somatic monitors, transmitting information to the cognitive centers of the organism. We can see why it would be a good thing to possess the trait in question: knowledge of possibly life-threatening states of the body is clearly useful knowledge to possess. You would want to know when you are about to starve to death or are dying of thirst or are being bitten by a tiger. Here consciousness functions as the body’s guardian and protector—and the body is all the organism has as a vehicle of survival and reproduction.
But what should we say about other kinds of consciousness, particularly sensory consciousness? These convey information about things other than the body, being directed to the organism’s environment: how can this be explained in terms of bodily preservation via knowledge of the body’s internal states? It can’t, not directly anyway. But the theory we are considering (the “somatic monitor” theory) is not without resources in replying to this natural question. An extreme view, not unheard of, is that perception never acquaints us with external objects; it is only ever directed towards the inner states of the organism. Thus every conscious perceptual act really conveys information about the body, given that there are bodily correlates to every such act. The organism lives in its own world and its sole concern is what is going on inside it. The only thing organisms ever really know about, then, is their own body—and that is no hindrance to survival (why be distracted by what goes on outside?). A second view, less radical and more plausible, is that all perception of the external environment is at the same time self-perception. This is evidently true for touch: when you touch an object you also sense your own body—touch informs you of external objects and of your own physical body (e.g. that your hand is grasping something). Likewise taste and smell bring awareness of bodily sense organs, as when food enters the mouth or aromas enter the nose. Hearing locates sounds in relation to the head and ears—possibly inducing such bodily reactions as blocking the ears from loud noises. The body is never out of the conscious picture, never entirely absent from what consciousness presents to the perceiving organism. Even in the case of vision we see things in relation to the body, this involving awareness of ocular motion, head orientation, and the state of one’s eyelids. I see things in relation to me, i.e. in relation to my body. Thus I may protect my body from seen objects that seem to threaten it—I don’t stare at the Sun, for example. So all the senses are bound up with the body and its parlous condition. Consciousness is always telling us about where our body stands and what might endanger its wellbeing. It evolved with this aim in mind—to keep the body in existence. Consciousness is the (mental) organ that enables the organism to manage its body’s affairs in a hostile world. Lastly, we might adopt an extended phenotype conception of the body, including in its extent the external environment: the organism is aware of its extended body when it is aware of what lies yonder, as when a spider is aware of its web or a beaver its dam. These entities need preserving too if the organism is to pass on its genes successfully; functionally, they are part of the organism’s phenotype. The body doesn’t end at the epidermis.
Accordingly, the model of hunger and thirst is not wide of the mark generally: these are the primordial forms that consciousness took back in evolutionary history, ultimately in creatures of the deep. Consciousness evolved in fish so as to keep the organism informed about its bodily state, both its subcutaneous organs and its surface features (fins, eyes, gills). It is ideally suited to this job because it has the property of epistemic privilege: it is exceptionally, indeed voluptuously, well known to its possessor. And conscious states are lawfully correlated with bodily conditions, thus yielding their existence and status to the organism’s epistemic faculties.  In consequence the organism knows what is going on within its body, this enabling it to act so as to preserve that body. It knows when its body needs food and water and when it is being dangerously impinged upon. If consciousness were not so closely connected to the epistemic faculties (and we mustn’t be too intellectualist about this), it would not have evolved: for the theory is precisely that consciousness evolved because of its epistemic privileges, combined with the ability of conscious states to indicate the condition of the body. This is the property of consciousness that explains its evolutionary emergence—its ability to pass the test of natural selection by reliably transmitting information about the body to the organism’s cognitive centers. Consciousness is like a messenger whose message we cannot miss or misunderstand, and whose central subject of communication is news about the body and its perils. It’s what the genes hit upon as a method of keeping track of what is going on internally. Consciousness is part of a biological mechanism designed to enable the organism to manage its body’s survival needs—for example, by monitoring its nutritive state. It is as if the genes decided to solve the problem of monitoring food intake by inventing the sensation of hunger, knowing that this is not likely to be missed by the hard-pressed organism (unlike, say, its actual physiological state of tissue nutrition). It’s a quick and easy way to keep informed about how your body is doing at any given time. It’s not the only logically conceivable way this vital task could be performed, as other biological adaptations are also not logically unique (birds could in principle have flown like helicopters or missiles); but it is the method that arose in the cut and thrust of practical biological evolution—the solution that cropped up at the time. Before that organisms did without consciousness, relying upon more mechanical methods of detecting and regulating their bodily requirements. But consciousness catapulted organisms to a new level of self-monitoring expertise, exploiting the epistemic privilege property of consciousness. This remarkable property is what gave it the advantage compared to non-conscious ways of ensuring that the body has what it needs to survive. So consciousness is really all about the body from an evolutionary point of view, a device for keeping the body safe and well and primed to reproduce. If there were no vulnerable biological bodies to take care of, consciousness would be unnecessary. Consciousness is one of the ways that evolution discovered to keep the body in passable shape; many organisms do without it entirely and get on just fine (consider bacteria or jellyfish).
A nice thing about this theory is that it brings consciousness resoundingly down to earth: from an evolutionary perspective, it is just another mechanism for ensuring the wellbeing of the body—a piece of machinery for keeping the body well regulated and free of damage. This is a good way to think about all biological adaptations—their raison d’etre is rigorously utilitarian. No trait takes root and is passed on unless it passes the stern test of natural selection—certainly not a trait as widespread as consciousness (sentience, awareness). It is truly biological. What exists within us, making us the thinking and feeling beings we are, is ultimately the result of a blind process that selects for bodily continuity. Preserving the body is what it’s all about, and consciousness does its bit in helping that to happen. It is body-centered, body-obsessed—just like the lungs, the heart, and the kidneys. Its interest in the world beyond the body is distinctly marginal, distinctly derivative. The external world matters only because it impinges on the body—the place where the genes live and have their being. Ultimately, indeed, the focus of the evolutionary process is on the reproductive organs of the body, these being the conduit through which the genes are passed on to future generations. We might even be so bold as to suggest that consciousness is genital-centric, since the genitals are the part of the body whose health is most vital to gene propagation. All the other organs of the body are dedicated to making sure that the reproductive organs get to perform their solemn duty at the highest possible level. If consciousness has anything to do with the soul, that is strictly a superfluous accretion, not part of the basic biological story—which begins with the fish, the insect, and the reptile. Consciousness is fundamentally all about ensuring that the body makes it through another day; and it achieves this aim by deploying its uncanny ability to be known with special intensity. 
 Proprioception is the prime example of this: the organism knows from the inside what the disposition of its body is. I wouldn’t be surprised if this was the very first sense to evolve, vital as it is.
 I could characterize this essay as Descartes meets Darwin: Descartes stressed the epistemic uniqueness of consciousness—its connection to certainty—while Darwin insisted that everything in the biological world is a product of survival-driven evolution. My proposal is that Cartesian certainty regarding consciousness plays a role in enabling the organism to keep its body in good physiological shape. In one good sense this is a type of naturalismabout consciousness. Certainly we need to pay special attention to forms of consciousness other than the human if we are to understand its biological roots. Of course, nothing in what I say is intended to rule out all sorts of elaborations and convolutions in the human case.