Evolution and the Self
We must assume that the self evolved, given that it exists and is not a social construct. That means it arose by mutation and natural selection, serving some biological purpose. And not just in humans but also across the animal kingdom: all those animal selves are biological adaptations, like limbs and brains and senses. The reference of “I” is a biological entity—its characteristics are biologically adaptive. An organism without a self is at a reproductive disadvantage compared to one with a self (other things being equal). The self does something valuable, survival-enhancing. One of its characteristics is unity (or at least felt unity), so this unity must have a biological function—it must make the organism better at propagating its genes (having offspring). There must be a “gene for self unity”, as there is a gene for vision or language or sexual desire (many such genes presumably). The architecture of the self must be connected to its functionality, just as in the case of the body. This doesn’t mean that the self is reducible to the genes or anything else of a material nature; it just means that the self is biologically functional.
But what job does it do—how does it aid survival? We are now accustomed to the idea of the modularity of mind, according to which the mind consists of an ensemble of separate faculties, each with its own inner structure and function. This is the orthodox ontology in the study of the mind: each module is an evolved organ, to some degree independent of the others, though interacting with them—a suite of innate capacities much like the organs of the body. This picture has fuelled some skepticism about the ontological status of the self: what need is there for a self in addition to the several components that compose the mind? Is it just a pre-scientific holdover from common sense, dispensable from the science of the human organism? What job could the self perform that is not performed by the modules we already have on board? Why not go Humean about the self and regard it as at best a misleading way to talk about psychological modules? There are the modules and there is the set of them, with nothing else needed. But this position flies in the face of a stubborn conviction that the self is real—we feel it inside us, we refer to it with “I”, and ethics is built around it. We should at least inquire if there is some adaptive purpose that it plausibly serves.
Actually I think the answer to this question is not far to seek: the self serves an integrative function. The self imposes unity on what would otherwise be disorganized plurality. The modules by themselves are a mere motley, separate departments or agencies of the mind, with distinct (and sometimes competing) voices. They need to be brought harmoniously together: but interaction is not enough—we need unification. The self is a superordinate entity that creates this unity. Let me put the point in terms of the brain: each module corresponds to a brain region (possibly widely distributed) that interacts with other brain regions; but in addition to these there is a further brain region corresponding to the unifying self—the self-center, as we may call it. It has its own identity and is not just the sum of the several brain regions corresponding to the mental modules. Just so, the self is a real entity apart from the modules it integrates, but it exists because of its integrative function: it evolved as a distinct “organ” so as to perform the job of unifying the separate modules that make up what we call the mind. For example, the visual and speech centers are connected—this is why we can report on what we see—and the self is the entity responsible for creating that connection. Hence the perceived unity of the self: its job is to create order from chaos—to unite the several voices belonging to the modules. Without it the mind would be a cacophony of voices, an unruly choir, instead of the unified entity we know it to be. If we imagine the mind evolving one module at a time, starting with a single module, we can see that there is a problem of integration to be solved: the self is the solution to that problem, and in due course it evolved. The self is the means by which the senses (etc.) come together. Thus it is a mental faculty in its own right—a distinct component of the organism. The human organism has a heart, kidneys, a brain, vision, touch, thought—and a self. These are all adaptations occasioned by the usual biological pressures. The self has an adaptive biology just like the heart, which is not to say that it doesn’t differ from the heart in important respects (there is no need to say that both are “physical”). It is not epiphenomenal or fictitious or a mere by-product of something else: it has its own biological rationale. Biology needs to expand to include it (it is one aspect of the biological adaptation we call the mind). We may assume that the self made its entrance long ago, well before humans ever came on the scene; for its unifying powers were needed just as soon as organisms developed multiple modules that needed integration. Of course, selves became more sophisticated over time, as the mind became more thickly populated with faculties, but the basic element is presumably very ancient, no doubt evolving in the seas. Then organisms could sense their own unity instead of being just a collection of autonomous modules. Selves piggybacked on modules, but they are something over and above modules; they certainly did not evolve before modules, since modules are their raison de’tre. They are how modules found their groove (the “groove theory” of the self).
It may be objected that there has to be something wrong with this picture, since modules contain mental states and mental states require subjects. If there is a pain module, it needs a subject for the pains to occur in—there is no subject-less pain. Experiences need bearers. But then the self could not have evolved subsequently to the modules and their contents: it was already present in the mere fact of experience. The point should be conceded, but it doesn’t refute the scheme I have presented, though it does call for a necessary distinction. Let us agree that the modules contain states that logically require bearers; that doesn’t imply that the self as it now exists doesn’t have an integrative function. The correct position is that the self has two basic ingredients: the primitive ingredient included in all conscious states (notice that this doesn’t imply a single self for each organism), and the higher-order integrative self that constitutes the reference of “I”. The structure of the self is thus two-tiered: the first tier as ancient as the first experiences to evolve, the second coeval with the onset of module integration. Your visual experience now has a subject-place logically built into it, but it also figures in the integrative actions of the self that unites it with other mental elements. We might call these the “subject self” and the “integrative self”. Both are evolved features of organisms, and both are presumably very old. Evolution builds on pre-existing structures, exploiting and repurposing them, and the self is no exception; it is a kind of tinkered together construction, made of primitive consciousness and higher-order integration. First, we have individual modules and the primitive subject; second, we have collections of modules and their unification into a single self. As is typical in evolution, there are no clear lines or unprecedented breakthroughs; everything is gradual accumulation and happy accident. The biological self evolved over eons, proceeding from earlier traits and driven by adventitious demands.
Animal selves are not all alike: it depends on the integrative needs of the organism in question. The bat must integrate its sonar experiences with its sense of touch, and both with its cognitive capacities. Thus we don’t know the nature of bat experiences and we don’t know what it’s like to be a bat self, since our selves don’t perform this kind of integration. Other animals don’t know what it’s like to be a human self, since our selves perform linguistic integration and theirs don’t. Integrative acts are common to different species, but not the items integrated. We know what module integration in general is like, but not the specific character of the integration an experientially alien species performs. What we would find really difficult to comprehend is a mind that lacked integration altogether—a purely modularized mind. Our minds are unified by our selves, but some possible minds may not be so unified; and this fragmentation is alien to us. We don’t know what it’s like to be a fragmented mind. Is it like having many selves or no self? Is there even a viable conception of self for such a mind? A new version of the problem of other minds would be this: How do I know that other minds are unified by a self as mine is? Maybe other people have fragmented modular minds with no unifying self to hold it all together (though their behavior may exhibit signs of unity). In some species there may be no single unitary self but several sub-selves (e.g. the octopus)
None of this is intended to solve the philosophical problem of the self, i.e. what the nature of the self is. The account is purely a theory of the biological function of the self—why it exists from an evolutionary point of view. It is easy to come to the conclusion that the self is biologically pointless–a remnant of the old notion of the soul perhaps–but the integration theory provides a rationale for the existence of the self as a product of evolution. How the integration works, what the nature of the self is, how it is realized in the brain—these are separate questions. But it may be helpful to start from a theory of what the self is designed to do, considered biologically. The existence of selves, in our species and others, is surely a biological fact, so we would expect there to be some biological function that selves serve. If consciousness helps us know the world, the conscious self helps us knit this knowledge together. It acts as a kind of counterweight to module plurality.
 To some extent we are all piscine selves, originally designed to integrate information from a watery world, joined with fishy feelings. Simple selves (actually not so simple) peek out from behind aquatic eyes, the ancestors of our dry-land selves. The fish self is the prototype of us all.
 Notice that in a classic case of modular divergence like visual illusion it is the same self that entertains both mental representations–there are not two selves corresponding to the two representations. We don’t have one self that sees the lines as of unequal length in the Muller-Lyer illusion and another self that insists that the lines are equal; instead one self brings both representations together. I see the lines as unequal and I (the same thing) believe them to be equal. The modules pull apart, but the self holds them together. The self operates as a device of module convergence. Are there any psychopathologies in which modular divergence is experienced as a splitting of the self?