The evolution of consciousness and the omnipresence of sentience

Based on the latest research, we can continue to maintain that sentience, and the higher order consciousness that springs from it in humans, is the most widespread accident in the history of life, completely unnecessary, but somehow omnipresent, or we can reject that view and assume it serves a deep evolutionary purpose.

Thought experiments can have a useful place in science and philosophy, allowing us to imagine a different set of circumstances or the rules that govern those circumstances, offering clarity where none had previously existed, but there are times when they serve to add more confusion than anything else.  Perhaps this is more true in the study of consciousness than other fields, where scientists and philosophers sometimes seem to spend more time discussing what consciousness isn’t or what it might be rather than what it actually is.  To be sure, some of this is because consciousness is extremely difficult to study, leading to a combination of subjective reporting about how people feel combined with a limited amount of data from experiments and an analysis of the underlying structures in the brain.  Unfortunately, our knowledge of how the brain works even beyond the extreme difficulties of consciousness is decidedly in its infancy.  We have mapped the major regions and the purposes they serve. We have documented the pathways from our sensory organs to the brain itself along with the different processes underlying how we glean information from the outside world. We also have a reasonably detailed understanding of the basic operations and structure of the underlying neurons, but putting it all together into a coherent model has proved elusive and our knowledge of how the brain creates a feeling of what is happening in the world around us is essentially non-existent.  Perhaps not surprisingly, this lack of knowledge has led in many cases for us to imagine the world as it might exist rather than as it actually does.  Chief among these ideas is the notion of an unconscious zombie, that is that we can replicate human consciousness without feelings or emotions, at least in principle, resulting in a being that behaves exactly as you do without experiencing the world as you do.  It’s certainly an interesting concept, helping us to consider what it means to be conscious as we are and potentially illuminating what it doesn’t, but it’s also at odds with the reality that unconscious zombies do not exist in the real world, or at least as far as we have been able to determine.  Evolution, for whatever reason, appears to have produced only conscious human beings, living in the inescapable present, presenting us with two options: Consciousness is some kind of weird accident, by product, or other meta effect, superfluous to our survival, or consciousness is a survival strategy that natural selection has favored.

Sadly, much discourse around consciousness in general favors the former, even if the reality remains unspoken, hidden in the shadows.  We tend to treat consciousness as if it was something extra at a minimum, a wild, amazing superfluity added in at the last moment, or even arising suddenly out of nowhere without any scientific explanation at all, some kind of weird accident rather the usual product of incremental changes accumulating over time with manifest benefits at each stage, benefits favored by natural selection, leading to greater and greater complexity, like the eye or the ear.  While this might be possible in principle and we cannot categorically rule out that one of our ancestors “awakened” one day as a conscious being for seemingly no reason, it seems near impossible in practice, unlike any other feature that defines us as biological organisms or that defines biological organisms more generally.  Putting this another way, there is no analog elsewhere in evolution, no complex structure or behavior that appears miraculously for no survival or reproductive purpose, and then happens to persist even at great individual expense.  When you consider how tightly consciousness is bound with our experience of the world and how impossible it is to separate ourselves from that experience, making it easier to saw off a limb than shut down our conscious selves, one has to wonder how anything so all encompassing could be an accident of any kind.  When you couple that with the extraordinarily high cost in energy to create conscious experiences in the first place, energy that could be used to make our muscles stronger or our reflexes faster, it seems even more unlikely it serves no purpose at all beyond an interesting curiosity.  On a perhaps more philosophical level, there’s also something deeply unsatisfying, at least to me, that the feelings which make the world around us so special, that color our every perception, that fill our mental lives, and one might argue make life worth living in the first place, are simply some random, nonsensical, unimportant development, one we could do without or even be better off without.

Fortunately for those who are unhappy with this impasse, new research on consciousness in animals could finally settle the matter in favor of an evolutionary perspective, even if we aren’t fully aware of the implications yet.  Simply put, we appear to be finding consciousness, or rather its more limited form, sentience, almost everywhere we look across the entire animal kingdom.  As the philosopher Jonathan Birch describes in his excellent new book, Edge of Sentience: Risk and Precaution in Humans, Other Animals, and AI, sentience appears to be far more broadly shared than we’d previously thought possible, present in almost every animal in every phylum, from humanity to the birds and the bees.  For our  purposes here, sentience is defined as the ability to have experiences that are directly associated with value judgments, either positive, negative, or neutral, and the ability to act on those judgments; to see something and feel it as good or bad.  Professor Birch refers to this capability as having “valanced experiences” and suggests the following criteria to determine if an organism is sentient:  The presence of senses to identify harmful stimuli that are connected to other parts of the nervous system, brain regions that centralize the processing of these senses, a response to drugs that can change an organism’s reaction to external stimuli and a tendency for the organism to seek those drugs when needed (for example, opioids for pain), the ability of the organism to make trade offs that balance risk and reward, to act flexibly for self protection, and to display some level of associated learning. In his view, the presence of one of these structures or behaviors is not enough to justify the possibility of sentience, while all of them would guarantee it and some of them would make the organism a candidate for sentience.  Based on this criteria, Professor Birch and other scientists now believe that all mammals are sentient, most if not all vertebrates are sentient including reptiles and fish, and many invertebrates including at least some insects are also sentient.  Unfortunately, the number of species that have been studied closely from this perspective is extremely limited, scattered across the various animal phylum and orders, making it difficult to generalize more broadly, but as it looks right now, we are finding evidence of possible sentience in just about every complex organism we study, even the “lowly” nematode worm that possesses a meager 285 neurons arrange in a ring in its head and less than two hundred more in the entire body.  Still, it appears to exhibit the ability to balance risks and rewards.  If presented with a food source on the other side of a chemical barrier, it will only attempt to break through if it reaches a certain hunger threshold.

Whether or not the nematode worm is sentient, we are left with three explanatory options for this state of affairs.  We can continue to maintain that sentience, and the higher order consciousness that springs from it in humans and potentially a few other species such as our cousins, the great apes, is the most widespread accident in the history of life, completely unnecessary, but somehow omnipresent, or we can reject that view and assume it serves a deep evolutionary purpose, either as something that arose extremely early and has been remarkably conserved for hundreds of millions of years, or one of the most common instances of convergent evolution yet discovered.  Even if we lack the necessary data to choose between either of the evolutionary perspectives at this time, both suggest that sentience carries with it a potentially decisive evolutionary advantage – and the potential means to test out which hypothesis is correct.  If sentience, or at least the roots of it, has been conserved since before vertebrates and invertebrates split, somewhere between five and six hundred million years ago, slightly before the explosion of life in the Cambrian Area, we might expect their to be a genetic basis for the phenomena, such as the HOX genes that define the body plan across all animals, but as far as we can tell, there is no such thing.  Genotypes build phenotypes, and the phenotypes of the brain vary substantially from order to order, meaning you cannot map a mammal brain onto a bird, much less a lizard or an octopus, which happens to have nine of them, one in the head and one in each limb.  This makes it extraordinarily unlikely that we will ever discover a gene or set of genes for sentience, which to many, might make the idea that sentience has been conserved for more than half a billion years equally unlikely considering it’s normally assumed that natural selection acts only on the genes themselves, but this isn’t strictly true.  While only the differences in genes can be passed down from generation to generation, the genes themselves can give rise to successful strategies that are themselves conserved even if the initial genetic underpinning shifts as lineages evolve along their own unique histories.  If sentience has been conserved in this fashion, perhaps the closest comparison would be to biological sex, which is present in most complex organisms, but doesn’t share a consistent genetic basis like the HOX genes.  Instead, there are a limited number of genetic pathways controlling development that are conserved within species, but the actual genes for sex determination vary widely, sometimes even with the same group of animals.  In birds and mammals the XY and ZW chromosome difference that determines an individual’s sex has remained stable over long periods, but in fish and frogs, for example, the situation seems to change rapidly as the genetic deck is shuffled.  Regardless of these different genetic mechanisms, most complex species have two sexes because it is a successful, some might say essential strategy for reproduction, enabling a constant commingling of genes impossible without it.

We might liken this to the make and model of a car that has been refreshed several times with newer, more updated editions over the years as technology has greatly improved.  The Porsche 911, for example, originally debuted in 1963 and while it’s still produced today, every single part has changed in the interim.  It is in all aspects, from how it is designed, to how it is manufactured, to what it is manufactured from, a completely different vehicle.  At the same time, key aspects of the original design remain, namely the rear engine coupé layout powered by a flat six motor with a certain, sweeping profile that makes it recognizably the same car even when it isn’t.  This, many would agree, is the “essence” of a 911 whatever its current or previous incarnations.  If we apply this analogy to sentience as a broadly conserved phenomena, we can consider the essence of sentience to be valanced experiences, and the conserved aspects to be the genes that guide the development of the neurons, the building blocks of brains. The combination of the two must support a configuration of the brain in each species that conserves the overall strategy of experiencing the world with feeling regardless of the specific underlying mechanisms.  If an underlying mechanism evolved that was incapable of supporting the sentience necessary for survival, it would not have been favored by natural selection and would most likely have died out.  In the past, we would expect to find the same as the present:  Almost every animal will be sentient, at least in its most limited form, though like moles who lost their eyes, there could still be organisms that found a way to survive and pass on their genes without it, likely making them important subjects for further study.  Conversely, the view that sentience is a convergent phenomena is markedly different, potentially evolving much later in evolutionary history and doing so many, many times.  In this case, if we could travel back in time, we would expect to find sentience in some animals, but not others.  We would also expect it to arise at different points in each animal’s unique history, or even not to have arisen at all.  Likewise, we would expect closely related cousins to be sentient in most species, and more distant ones less likely to be so.  We might also expect that creatures who aren’t sentient today didn’t have sentient ancestors, though sentience could conceivably be lost as with the conserved evolutionary approach.  Lastly, but perhaps most importantly, we should expect different types of sentience, not merely degrees.  This might seem hard to imagine, but it would liken sentience to something like the eye, which has arisen 40, 50, or even 1,500 times across about ten different designs currently present in living animals.  To continue the automobile analogy, it’s as though the tree of life were organized as different car companies.  Toyota and Honda design and manufacture different cars in (mostly) different ways, but there are some aspects of an automobile, four wheels, brakes, a steering wheel, a driver’s seat, etc. that are so important, every car has them.  While there are a few animals that make do without vision to fill certain ecological niches, having sight is so fundamental to success we can think of these outliers as being vehicles designed for a specific purpose that fail to conform to the normal layout.  Sentience, given its potentially equivalent frequency, would be the same, a strategy so successful that it appears over and over again, to the point where its absence is surprising rather than its presence, and yet when it is present, it’s not always the same.

It is necessarily difficult to say what different kinds of sentience might look like, but consider the situation if insects are indeed sentient.  While we have no idea what it feels like to be an insect, it’s no secret that it’s radically different than how it feels to be human.  For example, insects do not appear to experience pain in a remotely similar way.  As the naturalist and author, C. H. Eisemann described it in 1984, “No example is known to us of an insect showing protective behavior to injured body parts, such as limping after a leg injury or declining to feed or mate because of general abdominal injuries.  On the contrary, our experience has been that insects will continue with normal activities even after severe injury or the removal of body parts.  An insect walking with a  crushed tarsus, for example, will continue applying to the substrate with undiminished force.  Among our other observations are those on a locust that continued to feed whilst itself being eaten by a mantis; aphids continuing to feed whilst being eaten by coccinellids; a tsetse fly which flew into feed although half-dissected; caterpillars which continue to feed whilst tachinid larvae bore into them; many insects which go about their normal life whilst being eaten by large internal parasitoids; and male mantids which continue to mate as they are being eaten by their partners.”  Clearly, this isn’t the same kind of sentience we have, and perhaps for good reason:  It’s possible that pain responses in insects are managed very differently than our own, under decentralized control using the ganglia in the abdomen and the thorax, essentially smaller brains throughout the insects body, rather than the ganglia in the head.  This at least implies that sentience in insects doesn’t include the full feeling of what is happening to their entire body.  Whether this is because it didn’t evolve that way in the first place using the convergent model, or there was some split under the conserved model is impossible to say at this point.  The question, of course, is how to decide between the two when sentience leaves no fossil remains.  How can we say with any surety that a primeval fish was sentient even if we believe a modern one might be?

We cannot, but as we have seen, we can study animals in the present, comparing both their morphology and their genes.  In my opinion at least, if sentience were a trait broadly shared and conserved by evolution it would leave a far different pattern in modern animals than if it was a convergent phenomenon.  It could be widespread in both cases, but in the convergent case, we should expect to find many more gaps in more closely related species.  If for example, one branch of insects was sentient and another was not, it would be reasonable to consider whether it evolved after the two branches split.  We might not be able to say for sure, but there could be evidence in the organization of the brain or the genes that guide the development of the brain.  We can also consider why sentience was important to one branch of the insect family tree’s survival and not another.  Why might bees be sentient and not ants, for example?  While both are hive animals, they rely on completely different techniques to locate and secure food.  Ants march in different directions, leaving trails of pheromones in their wake for other ants to follow.  If a sufficient number of ants are going to and coming from the same spot, most of the colony will be led there by the chemical signature.  Bees, however, scout out locations on their own, remember the size, direction, and distance, then report back to the hive, where the find is voted on by others.  It’s certainly possible that one survival strategy requires sentience and one doesn’t, especially considering the bees’ survival requires complex decision making based on synthesizing multiple data points almost precisely as sentience supports, and we should likely be able to figure out why and whether that same reasoning applies to other animals.  Ultimately, pursuing the origin of sentience from an evolutionary perspective and finding evidence like this would simultaneously lay to rest the idea that consciousness is superfluous.  We might not be able to say for sure what evolutionary benefit sentient served at every step of development, but if we can determine whether it is conserved or convergent, it would have to have evolved for a specific purpose, settling an age old debate.  That alone would be worth it.