Evolution proceeds not only in the direction of greater diversity and more inclusive communities but also in the direction of increasing complexity and heightened awareness. In general, the more complex an organism is, the greater is its awareness.
Awareness belongs to all life. It is the capacity of a system to respond to stimuli – to integrate sensations from the environment with the creature’s immediate goals in order to guide its behaviour. The more complex the system, the more numerous and varied are its responses. Biological evolution proceeds by creating more sophisticated awareness and response systems. Over billions of years, it has created ever more complex sensory receptors and nervous systems, capable of interacting with the world with greater awareness and responsiveness. So there is a spectrum of awareness, ranging from simple awareness (possessed by all life forms from bacteria, through protists, plants and fungi, to invertebrate animals), to consciousness or perceptual awareness (possessed in varying degrees by all animals with nervous systems and characterised by a degree of inner life or interiority), to self-awareness (possessed, again in varying degrees, by a few animals with more elaborate nervous systems, including chimpanzees, orang-utans, dolphins, a family of birds known as corvids despite their having no cortex, perhaps elephants, and of course humans).
So while plants may possess very sophisticated awareness systems, they are not conscious in the sense that even a lowly mosquito is. And your pet dog, though possessing a significant level of consciousness, has no self-awareness or sense of “I” in anything resembling the way humans do. As in the visual spectrum there are no sharp dividing lines between the colours, so in this spectrum of awareness it is impossible to draw neat dividing lines between one level and another. At what level of complexity awareness blossoms into consciousness, or consciousness into self-awareness, is impossible to say.
We have scarcely begun to understand the awareness systems of the simplest organisms. Though they possess no sensory receptors as such, bacteria can detect the presence of food and of other bacteria competing for that food. Only yesterday, BBC News reported research findings, published in Biotechnology Journal, that bacteria can “smell” ammonia that indicates the presence of a nearby nutrient source. We now know that bacteria possess their own primitive equivalents of sight, touch, taste, and smell. Of the five senses that we possess, they appear to lack only hearing.
The invention of the neuron – a cell specialized for awareness – made possible an expanded awareness called consciousness. It belongs to all animals with nervous systems, and bestows on them a measure of inner life or interiority – a sense of being present to their world. Sensory neurons, activated by physical stimuli, send signals to the central nervous system (CNS) that encode information about the organism’s external and internal environments. The CNS processes the information to determine an appropriate response and sends output signals to muscles and glands to activate that response.
Such consciousness depends on “perceptual categories” being stored in the brain. The brain is in part a representational system that develops symbols to represent patterns of incoming sensory data. By matching sensory input with these stored perceptual categories, the creature perceives and understands what that sensory input means. We can only guess at what categories may occupy the brain of a mosquito. They may be limited to “food”, “convenient place to land”, and “potential mate.” Your pet dog, on the other hand, will have a great many more such categories stored in its brain, such as “ball”, “car”, and “go walkies.” The more perceptual categories that can be stored in a brain, the greater is that creature’s consciousness.
At some point in our evolutionary history, when brains became sufficiently complex to store a very large repertoire of perceptual categories, there began to emerge a sense of self. Mosquitoes have practically no self at all (which is why we can swat them so easily), while your pet dog has at least a rudimentary self-model – an approximate sense of itself as a physical entity in a larger world. Near the upper end of the spectrum are chimpanzees, orang-utans, dolphins, and corvids who have a sufficient sense of self to be able to recognize themselves in a mirror. And finally we come to humans – a creature with an infinitely extensible repertoire of categories, including some that are clustered into a clear perception of “me” and a stable sense of “I” – a creature whose self-awareness is such that we are spectators to our own awareness. We can witness our own thoughts and feelings, represent them in symbolic form in our language and art, and reflect on who and where we are in the larger scheme of things.
Such is the spectrum of awareness that has evolved over four billion years of life on this planet. It may be a stretch to say that this is the “purpose” of evolution. But it seems clear to me that, whatever may be driving it, this is the direction in which evolution moves – towards ever greater complexity and heightened awareness. And if we wanted to get mythic about it, we might even say that the planet is in process of awakening.
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