Some people point to language and the associated benefits as being the unique defining feature of consciousness. Conveniently, this viewpoint rules out all but one species, Homo sapiens (which has an ineradicable desire to come out on top), as having sentience. Yet there is little reason to deny consciousness to animals, preverbal infants [see “The Conscious Infant,” Consciousness Redux; Scientific American Mind, September/October 2013] or patients with severe aphasia, all of whom are mute.
None other than Charles Darwin, in the last book he published, in the year preceding his death, set out to learn how far earthworms “acted consciously and how much mental power they displayed.” Studying their feeding and sexual behaviors for several decades—Darwin was after all a naturalist with uncanny powers of observation—he concluded that there was no absolute threshold between lower and higher animals, including humans, that assigned higher mental powers to one but not to the other.
The nervous systems of all these creatures are highly complex. Their constitutive proteins, genes, synapses, cells and neuronal circuits are as sophisticated, variegated and specialized as anything seen in the human brain. It is difficult to find anything exceptional about the human brain. Even its size is not so special, because elephants, dolphins and whales have bigger brains. Only an expert neuroanatomist, armed with a microscope, can tell a grain-size piece of cortex of a mouse from that of a monkey or a human. Biologists emphasize this structural and behavioral continuity by distinguishing between nonhuman and human animals. We are all nature's children.
Given the lack of a clear and compelling Rubicon separating simple from complex animals and simple from complex behaviors, the belief that only humans are capable of experiencing anything consciously seems preposterous. A much more reasonable assumption is that until proved otherwise, many, if not all, multicellular organisms experience pain and pleasure and can see and hear the sights and sounds of life. For brains that are smaller and less complex, the creatures' conscious experience is very likely to be less nuanced, less differentiated and more elemental. Even a worm has perhaps the vaguest sense of being alive. Of course, each species has its own unique sensorium, matched to its ecological niche. Not every creature has ears to hear and eyes to see. Yet all are capable of having at least some subjective feelings.
The Austere Appeal of Panpsychism
Taken literally, panpsychism is the belief that everything is “enminded.” All of it. Whether it is a brain, a tree, a rock or an electron. Everything that is physical also possesses an interior mental aspect. One is objective—accessible to everybody—and the other phenomenal—accessible only to the subject. That is the sense of the quotation by British-born Buddhist scholar Alan Watts with which I began this essay.
I will defend a narrowed, more nuanced view: namely that any complex system, as defined below, has the basic attributes of mind and has a minimal amount of consciousness in the sense that it feels like something to be that system. If the system falls apart, consciousness ceases to be; it doesn't feel like anything to be a broken system. And the more complex the system, the larger the repertoire of conscious states it can experience.
My subjective experience (and yours, too, presumably), the Cartesian “I think, therefore I am,” is an undeniable certainty, one strong enough to hold the weight of philosophy. But from whence does this experience come? Materialists invoke something they call emergentism to explain how consciousness can be absent in simple nervous systems and emerge as their complexity increases. Consider the wetness of water, its ability to maintain contact with surfaces. It is a consequence of intermolecular interactions, notably hydrogen bonding among nearby water molecules. One or two molecules of H2O are not wet, but put gazillions together at the right temperature and pressure, and wetness emerges. Or see how the laws of heredity emerge from the molecular properties of DNA, RNA and proteins. By the same process, mind is supposed to arise out of sufficiently complex brains.