How is consciousness created? When did it first appear on Earth? How did it evolve and which living animals have it? Consciousness researcher Todd Feinberg has been pondering these questions for over twenty years, while biologist Jon Mallatt has been fascinated by the early evolution of animals for an even longer time, so in 2013 we teamed up to see if we could find some answers. Today, consciousness studies are undergoing a great surge of interest, as long-standing philosophical questions are starting to be addressed scientifically. In this book we draw upon the diverse fields of neuroscience, evolutionary neurobiology, and philosophy to answer these questions. We focus on primary or sensory consciousness, which is the most basic type and means just having any kind of experience at all. Using as a starting point philosopher Thomas Nagel’s proposal that conscious animals have experiences that constitute “something it is like to be,” we seek the evolutionary origins of central philosophical indices of consciousness such as John Searle’s “ontological subjectivity” and David Chalmers’s “hard problem of consciousness” (how the physical brain produces personal experience). By applying a range of recent discoveries about the nervous systems of many different kinds of animals, about animal behavior, and about evolution and ancient life on Earth, we aim to identify the date when sensory consciousness and animal sentience first appeared and the “hard problem” was created.
This book is written for a wide range of readers: those interested in big philosophical questions about life and meaning, in consciousness and brain science, the vertebrate and invertebrate animals, or fossils and deep time. These fields are vast and varied, but we strive to cover and join them all, presenting at least their basics without demanding that the reader has an expert background in any of them. Still, we did not skimp as we worked to present clearly such topics as the full anatomy of vertebrate brains, the defining philosophical axioms of conscious states as well as the brain structures associated with consciousness, the theories and controversies of consciousness research, the first explosive diversification of animals half a billion years ago, the role of the senses in survival, neural pathways, the various kinds of vertebrates and their evolutionary histories, learning in animal behavior, the origins of pleasure and pain, and even some invertebrate biology.
In the first part of this book, we explain the basic philosophical puzzles of consciousness and then begin to assemble a list of features that seem responsible for consciousness: the “correlates” of consciousness. With this list, we start to formalize our own scientific theory of consciousness called neurobiological naturalism, previously proposed by Feinberg, systematically laying it out here so that it can be adjusted by the discoveries of the later chapters.
Next, we consider the fossil record of animal evolution, as well as the living groups of animals that descended from the ancient ancestors. We examine the great “Cambrian explosion” of animal diversity, which occurred between about 560 and 520 million years ago, and produced all the known animal phyla (vertebrates in the chordate phylum, arthropods, molluscs, etc.). Most importantly, this explosion also produced the first complex nervous systems and brains, the first complex behaviors in animals, and the earliest evidence of animal cognition. We deduce that in the first vertebrates, our fishlike early relatives, something wonderful occurred. That is, these neural advances were accompanied by the first appearance of consciousness, when simple reflexives evolved into a unified “inner world” of experiences filled with the most mysterious feature of consciousness, called “qualia” or the subjective feeling of things. The first qualia we consider are mapped mental images of the external world as sensed by vision, hearing, smell, and the other “distance senses.” We refer to this as mapped exteroceptive consciousness. Challenging conventional wisdom and long-standing taboos, we then deduce that all vertebrates are conscious, not just humans and other mammals but also every fish, amphibian, reptile, and bird. All vertebrates have always been conscious, but we detect a large, memory-enhanced advance in sensory consciousness in the first mammals and first birds, when the end-site of consciousness switched from the lower midbrain (tectum) to the higher cerebrum.
While the book’s first half is about exteroceptive consciousness of the distance senses—experiences that can exist without any emotion—we next cover another fundamental aspect of consciousness called sentience that includes affect and entails positive and negative feelings. By surveying which animals living today show the behaviors and brain structures known to be associated with affective feelings, we deduce that all vertebrates past and present have affective consciousness, as well as mapped exteroceptive consciousness.
Then, having worked out the markers that identify both aspects of consciousness in the vertebrates, we apply these same criteria to the invertebrates, and find that the arthropods (including insects and crabs) and cephalopods (like the octopus) meet many of the criteria for exteroceptive and affective consciousness. This would mean that consciousness evolved simultaneously but independently in the first arthropods and first vertebrates over half a billion years ago.
The final chapter summarizes our findings about which animals are conscious, what brain regions are involved in its creation, and how consciousness first evolved. Consciousness in fact turns out to be a more diverse and widespread evolutionary adaptation than most workers in the field have realized. Our analysis leads us to update our theory of neurobiological naturalism. This updated version, still based fully on known biological laws and principles, is then used to tackle the most fundamental philosophical question of the nature of consciousness: how does the material brain create subjective experience? We find an answer in the transitions from reflex-to-image and from reflex-to-affect, as they occurred over 520 million years ago.
We gain even more insight by subdividing the problem, that is, by tracing the origins of four different aspects of consciousness: not only qualia (1), but (2) unity, or why the conscious experience is unified; (3) referral, or why conscious brains focus experience on the outer world and inner body, but never ever experience the workings of their brain neurons; and (4) mental causation, or how immaterial consciousness can cause changes in the material world.
Overall, our analysis of the neural origins of sensory consciousness attempts to cut through the Gordian knot of the mind–brain problem and provide a path of reconciliation between a philosophy of personal subjectivity and the objective structure and functions of the brain. It does so by chronicling the evolution of the first “conscious brains,” while also incorporating the neurobiological and philosophical aspects of consciousness.
The book’s special contribution is its finding that consciousness can be understood if we combine the evolutionary, neurobiological, and philosophical approaches. In fact, combining the three approaches is essential to solving the problem. Each approach has limitations that cannot be recognized unless someone considers the full picture from all three points of view. For example, the biological approach works to solve problems by reducing them to their most basic parts and then exploring the complex interactions between these parts, but the philosophical approach shows that such traditional scientific reductionism cannot solve the hard problem of subjectivity. Then evolutionary history resolves it by explaining why consciousness is both irreducible and natural. Our discovery that the triple approach is needed has important implications not just for consciousness science, philosophy, and paleobiology, but also for understanding ourselves in relation to the natural world and the animal kingdom.