PETER GODFREY-SMITH is something of an Oliver Sacks of cephalopods. The analogy isn’t perfect — he doesn’t attempt to diagnose or cure mental disorders in octopuses, and he lacks any long-standing relationships with them, though he certainly identifies individuals and their quirks. But just as Sacks could see the human condition reflected in individuals with profoundly different ways of perceiving the world from the norm, Godfrey-Smith asks in Other Minds: Who is like us? What makes a person live in her own mind, and recognize it as separate from the mind of another? Sacks asked such questions of people with neurological dysfunction, whereas Godfrey-Smith in Other Minds asks them of a species that is uncannily personable without being at all human. An octopus can gaze at you with what seems like a facial expression, changing color as if with a change in mood, even reaching out a tentacle to touch an inquisitive diver.

Scientists have known for decades that octopuses and their relatives can solve puzzles and navigate mazes, have camera-like eyes just as humans do, and seem more like vertebrates than the snails and jellyfish to which they are much more closely related. YouTube videos show them unscrewing the lids of jars to clamber out of confinement, or confounding their keepers by circumventing the experiments in which they are placed. They are capable of learning which food types are easier to acquire and remembering their discoveries for weeks at a time. They play. The famed oceanographer Jacques Cousteau mused on the octopus’s “soft intelligence.” But unlike other animals that we see as intelligent, such as great apes, or crows and their kin, octopuses seem unsettlingly alien.

Tracing the evolution of the cephalopod line from its earliest ancestors, Godrey-Smith wants to understand how it has arrived at a seemingly similar cognitive destination to our own. He is particularly interested in the moment in evolutionary time when organisms began to move around, enabling far more complex interactions with the environment than is afforded by a lifestyle glued to a rock in the ocean. It’s a long history, without many satisfactory milestones. About 600 million years ago, one-celled blobs evolved into mobile little saucer-shaped animals from the Ediacaran period, but these seem less than satisfactory prototypes for intelligence. As Godfrey-Smith puts it, the ocean at the time “was a garden of relatively self-contained and self-possessed beings. Macarons that pass in the night.”

Lines like this one make me grateful to have a mind like Godfrey-Smith’s at work on the topic at hand. A renowned philosopher, he takes the sparse scientific literature on octopus cognition, combines it with his own observations scuba-diving at “Octopolis” off the east coast of Australia, and then gracefully and unsparingly analyzes what these creatures can tell us about the mind, consciousness, and being human. He is not overly concerned with defining what a mind is, nor with any of the other tendentious minutiae that have caused many a book on consciousness to sink under the weight of its own prose. Godfrey-Smith is reasonably content with not having all the answers; indeed, one of the book’s many strengths is its humility and willingness to accept ignorance: we simply don’t know what consciousness is, or how language affects the ability to think. Of course, it may well be that philosophers pride themselves on such ignorance, so that clearly identifying something they don’t understand is almost as good as actually understanding it. Clearly articulated questions may be as useful as answers, at least some of the time.

Godfrey-Smith is intrigued by the octopus for some of the same reasons I like studying insects: they force me to throw away the crutch of close evolutionary affiliation that primatologists rely upon. Octopuses are like us, but they raise the question of how, and perhaps more interesting, why they are like us. Assuming we are both conscious, it is virtually impossible to suppose we inherited that quality from a common ancestor — we were last linked hundreds of millions of years ago, with many forebears in between who have the sentience of a breadbox. The octopus forces us to consider how the mind comes to be, separate from its existence in humans. In short, Other Minds doesn’t use the octopus merely as an excuse to talk about people, though to be sure it helps us understand the possible meaning of consciousness in both species.

When we look at those animals we find intelligent, whether octopuses, apes, or dolphins, we ask of each: What makes them special? Why do octopuses seem to have a different understanding of the world around them than eels, or anemones? Godfrey-Smith grapples with this question, and while he never conclusively answers it, he provides some compelling points to think about. Does their specialness lie, for example, in the way they can move, shaping their bodies to suit the world around them? Some scientists suggest that an understanding of where one’s body is in space is intimately tied to agency. Maybe, then, it’s all about muscle. But how does that apply to the Gumby-like forms of octopus and squid? Is the brain a kind of CEO, directing the body to do its bidding, which would mean that executing more complex shapes is a form of higher intelligence? And when in the process of evolution did animals “wake up,” to use Godfrey-Smith’s phrase? You don’t just evolve consciousness the way you evolve a fin instead of a leg, or a compound eye instead of a simple one. Or do you?

It’s hard to avoid chicken-and-egg scenarios when considering the origin of consciousness. Godfrey-Smith analyzes a wide range of psychologists’ and philosophers’ models for how humans came to know what we are, and tries to determine if any of these models apply to animals as different from us as the octopus. At times the reasoning becomes self-fulfilling: humans have a particular kind of brain, and a particular kind of experience, and we think we are pretty hot stuff, so any animal that seems like us in behavioral terms must perforce have a similar way of experiencing the world and themselves. He claims that “a form of subjective experience preceded late-arising things like working memory, workspaces, the integration of the senses, and so on. These complexities, when they came along, transformed what it feels like to be an animal.” Yet this insight still seems to me to search for what humans have, and assumes that if another animal seems human, that animal must have those things too. At the same time, Godfrey-Smith recognizes the limitations of projecting our own emotions onto others; he points out that pain, for example, seems to exist in many creatures that are otherwise vastly different from us. “You can still doubt that these animals feel anything, yes. But you can doubt that about your next-door neighbor.”

He runs up against two big stumbling blocks in seeing octopuses as rubbery versions of people. One is their lack of sociality — individuals in most species rarely interact except during mating, when the male risks being cannibalized by the female; and the other is their surprisingly short lifespans, which simply don’t allow for much learning and experience. Godfrey-Smith is shocked to discover that even the giant Pacific octopus only lives four years at most. Surely such personable animals should have at least the lifespan of a cat or dog! Their solitary lives in turn mean that communication among individuals is not particularly complex, whether in comparison with social mammals and other vertebrates or even with insects such as bees and ants. How much does language propel our brain evolution? Musing on this question, Godfrey-Smith points out that so-called higher order consciousness, in which one thinks about one’s own thoughts, may not be the linchpin for developing human-like experiences. Writers may have an inner voice, but that does not mean that such a voice is needed for thought.

One omission in the book is a consideration of how sex and sexual selection influence octopus habits and behavior. Godfrey-Smith refers to all the individuals he observes as “he” — understandable in a way because sex in octopuses and their relatives is hard to discern. But sexual selection has shaped so much about us — our large brains, for instance, may be the result of selection for mate attraction — that it is tempting to wonder how it has influenced the octopus. Octopuses and their squid relatives lack genitalia as we think of them, but the males have a specialized arm that they fill with sperm and transfer to the female. And while they do not live in groups, male and female octopuses must be able to find each other at the appropriate time, and presumably those best able to select mates and compete for them will have been favored by evolution. Cuttlefish engage in startlingly fierce battles for access to females, complete with rapid-fire color changes, biting, and the release of ink. In the blanket octopus, females can grow to be two meters long, but the males are only just over two centimeters, a size difference between the sexes that is larger than that of any non-microscopic animal. To put this difference in perspective, if we were like the blanket octopus, a human male would be less than an inch in height if the average woman is about five feet six, a sobering calculation indeed. How might these sexual differences, including, perhaps, an ability to sort through sperm from different males and select only the best, have shaped what octopus and their relatives are like, brains and all?

Godfrey-Smith also doesn’t directly address the ethics of eating, or even studying, creatures that seem self-aware. Then again, sentience is not what we think of first when we consider the inner lives of apes or dogs. Octopuses are animals that, while they may recognize and even respond to a human visiting their watery world, do not seem capable of loving you back, no matter how much you may love their squishy sentience. Some places have regulations about studying cephalopods that are in keeping with those governing the study of mammals and other vertebrates, but whether — or why — this should become universal is debatable.

The poet Ogden Nash was pithy in his summary of the octopus’s charms:

Tell me, O Octopus, I begs,
Is those things arms, or is they legs?
I marvel at thee, Octopus;
If I were thou, I’d call me us.

Nash was presumably referring to the collective of appendages in calling the octopus “us.” But for Godfrey-Smith, and maybe other people who get to know them, we might consider calling octopuses “us” for other reasons as well.

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Marlene Zuk is a professor in the Department of Ecology, Evolution and Behavior at the University of Minnesota and the author, most recently, of Paleofantasy: What Evolution Really Tells Us About Sex, Diet and How We Live.