Symmetry and the Mind
Symmetry is a pervasive feature of nature. We find it in atoms, molecules, crystals, planets and stars, as well as in the entire biological world, and also in human artifacts. Some things show no symmetry, such as rocks or puddles of water or sponges; but these are exceptions to the rule. Moreover, symmetry presents itself as the opposite of chance: symmetry suggests organization and order, not randomness and chaos. It also suggests harmony and beauty. The biological world appears to be run on symmetry, of complex and impressive kinds. Some organisms have radial symmetry, such as jellyfish, but the majority of more advanced organisms exemplify bilateral symmetry, which gives rise to a left-right structure. We have body plans based on a central axis of symmetry and duplication of body parts around this axis: two legs, two eyes, two ears, two arms, and so on. These appear as mirror images of each other, as counterparts, copies. An organism could be made of one of each and still be functional, but the duplication builds in redundancy, as well as cooperation between like organs. We can imagine planets with animal life not organized around symmetry, but if life on Earth is anything to go by, symmetry is fundamental to evolved life. Symmetry must be adaptive, despite what can appear to be pointless duplication (why don’t we find more parsimonious ceatures that make do with one eye, one ear, one hand, and so on?).
The abstract essence of biological symmetry is the cooperation of duplicate parts: each side of the body works together with the opposite side, to give more than one side alone can give. Two eyes are better than one, etc. This basic morphological principle extends to the brain, which itself is organized around a central axis into two similar hemispheres, as if animals have two brains that cooperate. The genes have built bodies that exemplify symmetry as a matter of biological law; and what the genes do they do for a reason. The genes themselves are symmetrical, with that symmetrical spiral of DNA. The idea of a duplication of parts clustered around a central axis is evidently deep and functional. Human art celebrates it; it is written into the daily experience of our bodies and other things; and it is difficult to conceive of a workable world without it (though it is frequently less than perfect or exact). The human animal, in particular, is a symmetrical being, and thus conforms to a basic principle of nature.
Yet there is a striking and strange anomaly: the mind does not appear to exemplify symmetry. The mind is a biological entity, evolved by natural selection, composed of parts (“mental organs”), housed in a bilaterally symmetrical body and brain, and yet it exhibits no apparent symmetry. Why? Why should the mind be an exception to the general rule? Why does it not contain separate duplicate parts that cooperate together? If the architecture of the body and brain involve symmetry, why does the architecture of the mind not? If symmetry is adaptive in the body, then why is not adaptive in the mind? Why is the mind plan so different, structurally, from the body plan? The mind does not appear to be organized into parts that are counterparts of other parts, with built-in redundancy, the whole working harmoniously together: it seems monistic, singular, undivided. We don’t, say, have a left-hand belief that snow is white and a right-hand belief that snow is white, or a left-hand desire for food and a right-hand desire for food. Nor do we have two wills or two selves or two faculties of reason or two language instincts or two moral sensibilities. We have only one of each, as if we had only one eye, one foot, one lung, etc. There is no psychological bilateral symmetry to match the symmetrical architecture of the body and brain. That seems puzzling from a design perspective. Nor do other animals differ: they too possess singular minds devoid of symmetry.
A number of responses to the puzzle are possible. One would be that symmetry is a geometrical concept and minds are not geometrical objects—so they cannot in principle exhibit symmetry (or asymmetry). As Descartes would say, the mind is not an extended substance, and bilateral symmetry requires spatial extension—parts in space that are duplicates of each other. But this response assumes that mind and body are radically separate; anyone who is less of a dualist will wonder why the spatially constituted mind does not exhibit symmetry (the brain does). Also, we can define analogue notions of geometric symmetry, as we do elsewhere when we apply the concept of symmetry (e.g. in logic to describe certain relations). The abstract notion of symmetry is just that of duplicate parts that work together, and the mind could in principle satisfy that more abstract notion. The mind has parts (beliefs, desires, and emotions, as well as faculties and modules), and so it is logically possible for it to duplicate those parts into a symmetrical architecture. But in fact this logical option is not adopted; it is pointedly rejected. The mind keeps itself stubbornly singular.
A second response is to question the appearances: maybe the mind exhibits symmetry in its underlying structure. For example, when we use our two eyes we see a single scene, yet the two eyes each send in their own separate images, which are then synthesized by the brain. The visual percept has a surface unity, it may be said, but it springs from a pair of symmetrical images, both on the retina and further into the nervous system. You can use one eye or the other to see, but the eyes work together to give a better image than each alone; nevertheless, the underlying process involves duplication and symmetry. And the same might be said of the ears or nostrils. Or again, more adventurously, it might be suggested that the mind is divided into two symmetrical halves, the conscious and the unconscious. Maybe the unconscious is the analogue of our left-hand side and the conscious of our right-hand side. Or maybe our moral faculty is the combination of an instinctive emotional system and a rational reflective system. The trouble with these suggestions is that the alleged symmetries are metaphorical and unpersuasive. It is true that the eyes provide a plausible analogue of symmetry, but what is striking is that the two images merge in the final percept—whereas the eyes themselves never merge. Visual consciousness does not consist of two separable but duplicate parts, as the body does. A real analogue would involve a creature with two visual images in its consciousness, yoked together somehow. This we never find. As to the other suggestions, it is farfetched to compare the conscious and the unconscious with the left and right hands: these are just two mental systems, not mirror images of each other working together. After all, the conscious and the unconscious are usually supposed to contain different contents, not copies of the same content. Crucially, what is lacking is some notion of pairs of beliefs or desires that act like parts of a symmetrically organized system—as it might be, left-hand beliefs and right-hand beliefs. Do we ever find ourselves going about our cognitive business using only our left-hand belief that the door is open and not our right-hand belief that the door is open? Hardly. It is not that each hemisphere stores its own copy of the same belief, which may be called upon to work together or separately, as with the hands or eyes. We have just the one belief or desire or emotion or intention or mental image. Our consciousness is not divided into two symmetrical halves like our body.
We can perhaps imagine a symmetrical psychological architecture: we postulate two selves each fully formed and occupying the two hemispheres (think of split-brain patients). Thus in my right hemisphere I have Self1 that has a full set of beliefs, desires, and so on, and a duplicate Self2 in my left hemisphere. These two selves might operate independently or in unison, just like my hands. That seems like a conceivable way to rig up an organism, and it has the advantage that if one self gets damaged or destroyed the other self is still there to carry on the good work. So it is perhaps surprising that such an organism has not evolved (as far as we know). In any case, that is not how things actually are, at least to all appearances: we seem to have a single self, with a single set of beliefs and desires, and with no symmetrical duplicate. In addition, each of these selves would fail to exhibit any internal symmetry, and be essentially just separate selves, not coordinated parts of a single functional entity. What is central to bodily bilateral symmetry is duplication plus unification: not two bodies with only one hand and eye each, but a single body with two hands and eyes. What is hard to imagine is a self (a psychology) that is both unified and bilaterally symmetrical. So there is something conceptual about the question, not merely accidental—we don’t just happen to have non-symmetric minds.
If we don’t have symmetric minds, do we perhaps have asymmetric minds? For this to be the case, we would need to be able to distinguish sides of the mind that stand in asymmetric relations—analogous perhaps to the claws of those crabs that have one hugely enlarged claw. Nothing immediately suggests itself, though one might draw attention to aspects of the mind that work against other aspects—as it might be, emotion versus reason. The idea of disharmony in the mind is not unheard of, or the idea of an unbalanced mind, or an ugly mind. But these are farfetched metaphors, rather than strict analogues: what we would really need is some notion of parallel systems that exhibit marked architectural diversity, such as two language faculties with different grammars (like two limbs with divergent anatomies). Granted the mind has separate parts, but the concepts of symmetry and asymmetry do not get any purchase on its overall structure. The mind is not like a symmetrical vertebrate body, but it is not like an asymmetrical sponge either.
So many things in the natural world are symmetrical—from spider’s webs and bird’s nests, to leaves and flowers, to reptiles and mammals, to worms and wombs—and yet the mind itself, in its many incarnations, is not one of them. Except where it engages with the senses in their bilateral symmetry, its organization is, we might say, anti-symmetric: it cancels symmetry. The mind receives inputs from the symmetrical body and sends outputs to the symmetrical body, but it itself exhibits no symmetry, no internal duplication of conjoined parts. It is one-track and single-minded, without even a central axis. It is like a sprawling metropolis with many add-ons and thoroughfares, but no overall symmetrical plan. It is, in one sense, disorganized. This is a puzzle because the mind is a biological product and yet it fails to possess one of the most salient marks of the biological.