One way to phrase the central question in the philosophy of mind is “why are we conscious?” We can answer this question by describing what consciousness is in general and then explaining why the physical properties of our brains result in this consciousness. This is how I usually attempt to answer the question, since it is these kinds of answers that are the most enlightening. However, we could also take the question in the historical sense, as in why did evolution result in conscious systems?
Our first intuition would be to say that consciousness has some beneficial effects, and thus evolutionary pressures selected for it. However, as we have come to understand consciousness more fully, it has become clear that consciousness is distinct from intelligence, and it is intelligence that provides the many benefits that we would naively attribute to consciousness. In fact the behavior of every conscious system could be replicated by some non-conscious system, and since evolution selects for behavior that should lead us back to square one, wondering why we (and possibly many other animals) are conscious.
The answer, which I will get to in due time, partly rests on the fact that consciousness is robust. The range of processes that result in the phenomena we call consciousness is quite large, all it takes is some basic structural facts, facts about how information is organized within the system at a given moment, and how the system develops over time. There are more than theoretical reasons to believe this; we have records of patients suffering from a wide range of brain damage, some severe, some minor, all of whom seem conscious. It is rare for a patient to be left alive but without consciousness due to brain damage (and even rarer for that patient to be in an awake state). And so we conclude that the facts about the brain that result in us being consciousness are fairly basic and simple, which is why it is so hard for them to be interrupted by damage.
So we know that natural selection will lead to some kind of intelligence, and ability to learn, since some organisms need these abilities to survive and complete successfully with each other for limited resources. My hypothesis then is that the simplest route to intelligence is consciousness. It is true that organisms with completely unconscious processes could have arisen, but in general evolution favors the simpler solution (since evolution proceeds by tiny steps, and thus the simpler solution would be reached first, and out-complete any organisms that were “on track” towards the more complicated, and non-conscious, solution).
To support this hypothesis it needs to be shown that the simplest path to useful intelligence is a conscious system. Previously I detailed three properties that a system must have in order for it to be considered conscious: a first person perspective, experiences, and self-awareness (and of course the appropriate causal connections within the system to support and sustain these properties). Experiences are obviously a given for all form of life that perceive their environment, process that information, and then react to it. It is true that very simple organisms, such as bacteria, have no need for experiences, they can survive with hard-wired responses to external stimuli. More complex animals, however, need to bring the information from their senses together so that whatever mental facilities they possess can be brought to bear upon it, and this is the essence of experience. The first person perspective would also be a natural improvement on the road to better intelligence, since an animal whose experience is structured around a perspective will be better able to tell what information is relevant to its survival. Although the first person perspective by itself doesn’t make the animal more intelligent it enables the intelligence the animal has to make better use of experiences. Experience, as mentioned previously, is how perceptual information is made available to the developing mental faculties. Perception, however, is not the only useful source of information, information about the animal itself can also be important, for example in deciding what needs have the highest priority. This is where self-consciousness comes in, integrating information about the animal’s current condition and capabilities into its experiences. Finally, we must consider if the causal connections required for consciousness would be selected for (specifically that a given experience can contribute causally to the animal’s knowledge about itself, for example by building new concepts or forming memories, and that each experience is always in some way incorporated into the next). It would seem like the path to increased intelligence would indeed select for these connections, since allowing experiences to build on each other provides for the possibility of more complex thoughts, ones that could not be completed in a single moment, and allowing experiences to permanently affect the mind allows for the ability to learn, also an evolutionary advantage.
If it is indeed the case that consciousness is a result of evolutionary pressures favoring intelligence, as I claim, it would explain many of our intuitions about consciousness in animals. For starters if evolution does lead to consciousness then we really do have a good reason to believe that some non-human animals are conscious. If they are far enough along the road to intelligence then it is likely they already have experiences, a first person perspective, and self-consciousness, since these abilities seem like pre-requisites for any evolved intelligence that is sufficiently bright. It would also explain why not all animals seem conscious. Evolution doesn’t favor a high intelligence in many cases, and so animals such as insects and fish simply haven’t developed the capacities necessary for consciousness.