This incredible book explores the origins of subjective experience by studying an animal—the octopus—that appears to be an unlikely candidate to provide insights into one of the most human of attributes: consciousness. After all, octopuses live near the ocean floor as mostly solitary creatures with abysmal social lives. They are members of the cephalopod family, which also includes the squid, cuttlefish, and nautiluses (deep-sea Pacific Ocean shellfish). How could a creature that is closely related to the mollusk (a phylum that includes clams, oysters, and snails) contribute to our understanding of human self-awareness and intelligence? On the surface, this sounds preposterous. However, Peter Godfrey-Smith, a distinguished philosopher of science at the University of Sydney and a skilled scuba diver as well, successfully takes on this assignment in Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness.
One can legitimately question why Godfrey-Smith’s story about how nature—or creation—became aware of itself features a protagonist that is alien to the human species. It seems that it would make more sense to talk about nonhuman intelligence—which to a degree is a requirement for consciousness—by starting with mammals or at least birds. These animals are known to possess high levels of cognitive functioning exhibited in the form of learning, memory, and decision-making. But perhaps the octopus is smarter than we think. Certainly Other Minds makes a compelling case that this is so.
What are the earliest and simplest animals that had subjective experience of some kind? To answer this question, we need to trace the evolutionary development of sentience, an organism’s ability to feel and perceive. Why? Because sentience comes before consciousness. A good candidate is the octopus. It is an evolutionary “old” animal in that during the latter part of the Cambrian explosion, which took place approximately 542 million years ago, we find the emergence of eyes. Eyes require a lot of processing demands, achievable only with the development of more complex nervous systems. The typical octopus that is found in the ocean today is similar to fossil records dating back 164 million years. These records reveal a strange creature that has already lost the shell from its mollusk ancestors; without an endoskeleton, it does not have a defined shape. However, in contrast to other earlier animals, the octopus possesses a nervous system that is made up of 500 million neurons. This is an extraordinary large number for such a small creature. As a basis of comparison, it is equivalent to what is found in a dog; it is virtually half the number found in the human brain!
Why do octopuses have so many brain cells? Godfrey-Smith argues that, as predatory animals, they need to be mobile. Yet, because of the unique properties of the cephalopod body—there is no shell or skeletal system—a vast range of movements is possible. This problem is solved by a nervous system that is a mixture of local and centralized control. In a sense, an octopus contains multiple brains in the form of ganglia distributed throughout its body. In fact, there are more neurons located in its six arms than in its head.
The outcome of having this large nervous system is intelligent behavior. Octopuses can learn how to navigate a maze in an artificial lab environment; they can learn to unscrew a lid from a jar, learn how to activate a lever to acquire food (operant conditioning), and recognize individual humans, even when they are wearing similar clothing. Less scientific, more anecdotal reports reveal an animal that appears to play with novel objects placed in its tank, a creature capable of eliminating a light source (which it does not like) by squirting jets of water at the bulb to destroy it. All of this is to say that octopuses appear to possess the raw intelligence to be creatures that are subjectively aware, albeit they do this with a “brain” that is very different from what humans have been given. In the words of Godfrey-Smith, “the octopus is the closest we will come to meeting an intelligent alien.”
Godfrey-Smith tries to unpack how subjective experience can be used as a portal into understanding consciousness. For him, subjective experience varies along a continuum. In relating this to human experience, imagine the act of falling asleep. There are various degrees of mental grogginess that one can feel prior to losing consciousness. Our level of awareness is altered during these stages as we become more and more unaware of our surroundings. For Godfrey-Smith, the notion that subjective experience has varying degrees is key for understanding the question: What does it feel like to be an octopus, and how does it compare to human consciousness?
In Other Minds, “consciousness” is seen as a “mixed-up and overused but useful term for forms of subjective experience that are unified and coherent in various ways.” Think of it as a sophisticated form of subjective experience that is dependent, in part, on memory systems and other cognitive processes that are usually found in intelligent animals. This interpretation raises a question: How unified and coherent does subjective experience need to be in order to reach a level where we can say that consciousness is present? Setting this problem aside, there is sufficient material in the book to draw some comparisons between the subjective experience of an octopus and a human.
First, many models of consciousness discuss the importance of “binding” or integrating information from multiple sensory, cognitive and emotional processes. Although scientists have never located a single neuroanatomical structure where this occurs, there is agreement that multiple structures within the nervous system requires extensive interconnections. Humans possess a vast network of interconnected brain structures; the octopus does not. The nervous system of the octopus is distributed throughout its head and body. It appears that processing is much more localized (e.g., each of the six arms has its own ganglia to interpret sensory stimulation), which would be indicative of a more primitive nervous system that does not afford the ability to engage in meaningful levels of self-awareness.
Second, animals with higher levels of intelligence require longer periods of time for the brain to reach maturity. In humans, profound neurobiological changes occur within the brain up to and including the teenage years. Research has also found important processes associated with insulating neurons continues in the adult mammalian brain through the third decade of life. Time allows complexity to find a foothold in the brain. By contrast, the average life span of the octopus is between one and two years. Why it is so brief, no one knows. What is known is that the nervous system of the octopus must develop rapidly. This speed/complexity tradeoff is a compromise that cephalopods must accept. However, their brief life places limits on the trajectory of development of the nervous system. This is another characteristic that makes it difficult to conclude that they reach levels of subjective experience that in any way approximate human consciousness.
Other Minds is written in a highly personal, engaging style. Although Godfrey-Smith explores challenging scientific themes, he is careful in choosing nontechnical language whenever possible so that the book can be read by a general audience. There are several chapters in which the author describes his intimate personal encounters with octopuses. These are rewarding sections of the book because they give a riveting account of what it is like to enter the world of these alien creatures.
Like many of his peers, Godfrey-Smith is resolutely committed to philosophical naturalism. But it isn’t necessary to share that outlook in order to enjoy and profit from his book. “There are many reasons for us to appreciate and care for the oceans,” he writes in his concluding paragraph, “and I hope this book has added one. When you dive into the sea, you are diving into the origin of us all.”