How did consciousness evolve? An excerpt from ‘A History of Bodies, Brains, and Minds: The Evolution of Life and Consciousness’

Defining consciousness has been a subject of debate ever since humans have had a sense of their existence. Consciousness is inextricably bound to the workings of our brain, but how neurophysiological processes become the internal, subjective experiences that make up sentient life remains obscure. And the scientific theories of consciousness are still quite far from converging into an agreed perspective.

In my book “A History of Bodies, Brains, and Minds: The Evolution of Life and Consciousness,” I provide a history of biological life focused on key events in brain evolution that set the path toward consciousness and explore some of the major theories that attempt to define how consciousness came to be.

Current theories of consciousness seek to understand its nature from different angles. Some theories center the conversation around basic internal feelings, such as pain or visual perception, and relate to the notion of sentience. Others highlight more elaborate phenomena, such as forming an autobiographical memory or being able to coordinate future complex actions.

In Chapter 14, I discuss the neural mechanisms associated with consciousness, and some theories about its emergence and evolution. It is not possible to do justice to all the theories of consciousness, so I focus on two prevalent ones that have been the most discussed in recent years—the integrated information theory (IIT) by Giulio Tononi and the global workspace theory (GWS) by Bernard Baars and Stan Franklin. The IIT refers to an encapsulated network in the brain with such high interconnectivity that it works as an indivisible whole. The GSW, on the other hand, proposes a globalized space where different cognitive processes converge to generate a multidimensional map from which decisions and courses of action are produced.

Both theories address distinct aspects of consciousness and make some predictions about the anatomical processes that might govern conscious states. But, in my view, neither of these theories alone explains the basic question of how the skein of neuronal activities generates an internal, subjective experience.

Throughout this chapter, I address some critical questions, such as when consciousness emerges in biological evolution and human life, and if it could be found in artificial systems, such as large language models. The following excerpt focuses on the pre- and postnatal aspects of human consciousness, the implications of its existence in animals, and the subjective nature of consciousness in all living beings. I hope to provide new perspectives and fuel further discussion on these intriguing topics.

The Birth of Consciousness:

When did consciousness emerge in evolution? Which species can be considered to be conscious? When do babies acquire consciousness? Although neuroscience has developed without the need to address these questions, an increasing number of neuroscientists and other scientists are now asking themselves how and when consciousness arises in the natural world.

Perhaps a first insight into these problems can be attained by addressing the development of consciousness in human development, in order to envision a sequence of stages leading to the capacity of conscious report. As said, according to the Integrated Information Theory (IIT), consciousness might not require exposure to external stimuli and might be present already in the fetus. Being optimistic, a measure of consciousness like the Φ value of the IIT might yield some clarity as to when the brain network acquires properties that can yield consciousness in human prenatal development (there could even be several thresholds indicating different degrees of integration). Some authors have suggested that human consciousness arises at about 35 weeks of gestation, when the thalamus starts driving cortical activity and the electroencephalogram becomes patterned by continuous waves. Another possibility (which I consider more likely) is that while the human fetus might have a basic internal organization as specified by the IIT, consciousness may develop after birth, when the subject engages in interactions with the surroundings and with others. According to some researchers, the postnatal development of consciousness is a process of continuous learning throughout our lifetime, in which, guided by sensorimotor experience, the brain networks feed their activity patterns into other networks as well as into themselves in an expanding spiral, where again interactions with the environment are crucial. As I said, language may provide a mechanism to amplify these phenomena by enabling us to produce increasingly abstract mental events.

Animal Minds?

Another critical and current problem refers to animal sentience or consciousness. Anyone who has had a dog or a cat as a pet can witness their expressions signaling what one could call at least emotions. Furthermore, experiments described in chapter 9 suggest that animals might be able to make ‘mental maps’ of space. This issue has strong implications in the domain of bioethics, where increasing regulations are being imposed about the welfare conditions, not only of animals commonly used as food and in research laboratories but also among pets that by the way have given rise to a profitable industry around them. In its strongest expression, some activists claim for animal (and even nature’s) rights, which poses great problems about the limits of these rights in conditions that they cannot be obliged to any responsibilities, and of determining which animals will qualify for which kinds of rights. It may become illegal to boil living lobsters, but will it come a point where we cannot eat them, together with mollusks, fish, chicken, cattle and even insects? Where do we draw the line?

Again, the key issue is how to detect sentience or consciousness in other animals. The IIT has provided a criterion for basic consciousness (perhaps a form of sentience), but this is experimentally very difficult at this point. Another approach could be to assess behavior, but then the interpretations of the results are usually being contested. The experiments of self-recognition in a mirror were initially used to verify self-consciousness, but it was found that some fishes can pass the mirror test, suggesting that this ability is based on simple brain mechanisms (see chapter 8). Many studies have addressed metacognition in nonhuman animals, like assessing one’s chances to solve a task or having a sense of body size, but again there may be simpler explanations for these findings. A more subtle experiment took advantage of a well-described “double dissociation visual awareness” task in which people perform in totally opposite ways whether they have consciously processed a stimulus or when they have unconsciously processed it (this is different from not perceiving the event, as there is a stimulus-related response). When applying a version of this task to macaques, these animals developed double-dissociation responses much akin to those in humans, which suggests that there is a difference between conscious and unconscious processing in this species. Yet, the difference between unconscious and conscious perception could rely on different neuronal activities, with consciousness being only an epiphenomenon.

Rather than finding an absolute indicator of nonhuman consciousness, perhaps a more fruitful approach to a comparative study of the mind is to recognize different indicators of consciousness and determine how these parameters are distributed among animals. This implies that consciousness and subjective experiences may not be equivalent for different species, as, for example, in an echolocating animal versus a highly visual animal like us. Nonetheless, some general mechanisms may be associated with increasing degrees of consciousness. Using a sort of scala conscientia, as indicated in figure 14.1, may work as a good reference guide for these processes.

All in all, research in animal consciousness faces the same challenges as the study of human consciousness. First, Chalmer’s hard problem, which recognizes the ontology of mind but claims the incapacity to explain it in materialistic terms, leaves the issue of animal subjectivity as an eternal unknown. Secondly, Dennett’s hard question (then what?) could be stated as whether consciousness itself confers any selective advantage or rather if it is the material complexity of the brain and the consequent cognitive capacity that provide evolutionary benefit. Some authors argue that consciousness promotes survival in the face of contingencies and facilitates the evolution of culture and societies, but again this would be very hard to show.

Mind and Matter:

In the end, the dualistic dilemma between subjective experience and mechanistic explanations seems to me inescapable. Denying its existence as an illusion appears unsatisfactory to me. Some scholars argue that as with the conception of life, which was once considered to be a spiritual phenomenon and was explained by science, the problem of consciousness will also be resolved with scientific research. However, life is a scientifically observable phenomenon, while our subjective experiences are not accessible to third parties. Furthermore, for conscious subjects, their own life is an experiential phenomenon as well. One alternative to get away from the mind-body conundrum has been pan-psychism, which is an extension of the identity hypothesis, proposing that some degree of consciousness is a feature of the universe like energy or gravity are. As prescribed by the IIT, the subjective experience may be a widespread phenomenon among living beings that amplifies with the increase in complexity, and in particular may have exploded like a ‘big bang’ with the origin of large brains, giving rise to fully subjective consciousness.

Some other researchers, particularly physicists, have moved much farther, proposing that the source of consciousness relies on quantum mechanics. In this view, quantal superpositions of states in elementary particles would collapse wave functions into (proto-) moments of experience composed of basic qualia, the fundamental ‘particles’ of consciousness. Many prestigious authors have endorsed this view in one way or another. While quantal panpsychism is highly controversial and not accepted by many scholars, it makes some predictions, one of which is that quantum computers might eventually gain consciousness by this process (but again, how would we know?). Finally, while panpsychism may be an intriguing possibility, this perspective runs the substantial risk of anthropomorphizing nature, projecting human experiences onto much simpler beings whose subjectivity, if it exists, might be radically different from ours. We need to keep present that our mind is practically unique (at least on Earth), and results from having an extremely complex brain endowed with language. Other kinds of subjective experiences are probably much simpler, or different, or many times simply negligible to be considered as relevant.

Perspective:

Consciousness is perhaps the most difficult to define of all biological and cognitive categories, yet it is at the same time essential to our existence. It refers primarily to the qualitative experience of being the protagonists of a world independent from us, which includes the capacity to observe our own bodies and to sense our internal selves. Here I adhere to a sort of scala conscientia with different stages of increasing complexity that might give rise to human consciousness, which is vastly amplified with the acquisition of language. However, despite the apparent relation between consciousness and complexity, how material mechanisms become transformed into a first-person qualitative experience poses a major problem for neuroscientific research, which is conceived to deal with second-person observable phenomena. Because the unobservable nature of subjective states by second parties severely limits their scientific study, some have decided to downplay them as an irrelevant illusion generated by our complex brain networks. Whether consciousness is or is not relevant for our decisions and behavior is a debatable issue, but the illusion argument does not really explain to me how subjectivity is in fact produced.

Perhaps acknowledging these difficulties, neuroscientists have started to search for the neural correlates of consciousness (NCCs), which imply patterns of neural activity that fit reported conscious states. Yet, a correlation does not imply causation and is even less an explanation. In this line, two main theories have been proposed to account for the NCCs: the IIT and the GWS. The IIT, on the one hand, prescribes a tightly encapsulated dynamical network that works as an indivisible whole, providing the unified property of conscious states. On the other hand, the GWS refers to a ‘central executive’ system that receives multimodal signals from the body, the exterior, and from memory, and organizes these inputs to generate a simple working model. It is likely that both theories are in fact addressing conscious phenomena at different levels: The IIT refers more to a primary consciousness, whereas the GWS refers to the executive aspects of extended consciousness.

Finally, another major question is whether consciousness can be found beyond human existence. The claims for animal sentience and consciousness have recently increased, even among scientists. The application of indicators of a scala conscientia in the tree of life, considering an important degree of diversity, may provide a useful tool to examine at least the cognitive elements that are associated with conscious states. However, in my opinion, the hard problem of subjectivity remains inescapable. Some authors propose pan-psychism, the notion that consciousness is an everywhere byproduct of matter, which elaborates with material complexity. For some physicists, psychism could be somehow related to quantum uncertainties. In the next and final chapter, I will discuss where evolution may lead our species, our brains and our minds.

Excerpted from “A History Of Bodies, Brains And Minds: The Evolution of Life and Consciousness,” by Francisco Aboitiz. Reprinted with permission from The MIT Press. Copyright 2024.