Octopuses—those rascally, shape-shifting, skin-changing, critters of the sea—are, like all forms of life, unique. Watch them—as they scamper across the sea-floor, open a jar from within, change the color of their flesh in a heartbeat (of which they have three) through a startling range of colors and patterns, wield coconut shells or seashells as tools, or ensnare an unlucky target in an elegant tangle of tentacles—and you behold a creature seemingly extraterrestrial in its form, yet somehow familiar in its mental faculties.

Consider Inky: Previously a captive denizen of the National Aquarium of New Zealand, Inky made headlines this year after he managed to slide the lid off of his tank, climb up and out of it, slither across the floor, squeeze through a drainpipe, and return to the ocean, an episode described by National Geographic. “He was very inquisitive,” the manager of the aquarium told that publication, “and liked to push boundaries.”

Aristotle had a different take on Inky and his ilk. “The Octopus,” he wrote in the History of Animals, “is a stupid creature, for it will approach a man’s hand if it be lowered in the water…” What others might see as a sign of inquisitiveness, Aristotle took for idiocy. To his credit, Aristotle did accurately describe some of the other aspects of the octopus, including its ability to change “its color as to render it like the color of the stones adjacent to it” while hunting, or when startled. He also described its precarious and short life, and the death that comes soon “after the birth of the little octopuses.”

Wily, short-lived escape artists and masters of disguise, perhaps. But can we say more? Can the beasts think? Can they feel? Do they have, that is to say, the gift—and sometimes the curse—of consciousness?

“Plato,” Bertrand Russell began his essay Mind and Matter, “reinforced by religion, has led mankind to accept the division of the known world into two categories—mind and matter.” This dualism was famously reformulated by René Descartes, who also pinpointed the essence of the mind to a rather curious part of the brain, the pineal gland. Although many have since sought to call the mind-matter question a closed case (including Russell, who concluded that the “whole problem vanishes” if only people accepted his argument), the question of “mind”—or more precisely, the problem of consciousness—remains as thorny as ever. Why do we consciously perceive the world, and with what living things do we share this faculty?

The essence of the question is perhaps most clearly posed by the philosopher and pioneering thinker on consciousness, David Chalmers. “Look, I’m not a zombie, and I pray that you’re not a zombie,” he told Oliver Burkeman of the Guardian, “but the point is that evolution could have produced zombies instead of conscious creatures—and it didn’t!” By this Chalmers meant that it is theoretically possible that living creatures, including humans, could conceivably engage in all sorts of behaviors and actions without a corresponding sentience of them.

A robot, in other words, can retract an appendage from a scalding surface without suffering from it—indeed, human beings already do this, for we reflexively withdraw from pain prior to the conscious perception of it. And when two paramecium bring their single-celled bodies close together, fuse membranes, and swap some DNA, they are engaging in a form of sex, yet neither party (it seems safe to assume) has any experience of it at all, much less the intense pleasure human beings from time to time enjoy. Simply put, organisms don’t—at least in theory—need to have the conscious experience of suffering to flee pain, nor must they have lustful gratification in order to pursue sex: A circuit board, or a complex cytoplasmic cascade of chemicals, might—without conscious perception—theoretically produce the same (or at least roughly similar) results. 

Despite the long philosophical lineage of this debate, it is only in recent years that consciousness became a legitimate subject for scientific inquiry. As neuroscientist and consciousness researcher Stanislas Dehaene describes in his 2014 book Consciousness and the Brain: Deciphering how the Brain Codes Our Thoughts, until the late 1980s, consciousness research was seen as a somewhat quixotic and unscientific pursuit that might be dangerous for one’s career (it was the “c-word,” and could not be uttered in laboratory meetings). Burkeman writes how in 1990, the biologist Francis Crick used his fame to break the ice on the subject, and assert (along with scientist Christof Koch) that this was a problem that scientists needed, at long last, to tackle.

A philosophically and scientifically fascinating endeavor, no doubt: Yet the real-world consequences of the consciousness debate must also not be underestimated. An understanding of animal consciousness could have enormous ramifications for questions of animal rights. Even more important, as Dehaene describes, a better understanding of human consciousness—and altered states thereof—has all sorts of implications for the diagnosis and even treatment of conditions of disordered consciousness, like coma. Perhaps we might develop tools, for instance, that could let us predict which patients in a coma will “wake up”—and which will not. Might there be something to be learned about consciousness from the octopus?

“What are the earliest and simplest animals,” philosopher Peter Godfrey-Smith elegantly asks in his delightful new book Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness, “that had subjective experience of some kind? Which animals were the first to feel damage, feel it as pain…Does it feel like something to be one of the large-brained cephalopods, or are they just biochemical machines for which all is dark inside?” 

OTHER MINDS: THE OCTOPUS, THE SEA, AND THE DEEP ORIGINS OF CONSCIOUSNESS by Peter Godfrey-Smith Farrar, Straus and Giroux, 272 pp., $27.00

We are all, of course, mere biochemical machines. But out of that biochemical machinery there coalesces a magnificent state of consciousness, through which we experience an injury as an acute pain, orgasms as intense pleasures, or the consumption of certain foods—oysters, for instance—as either pleasure or pain, dependent on one’s tastes. Or, as Dehaene rather unromantically puts it, “All our conscious experiences, from the sound of an orchestra to the smell of burnt toast, result from a similar source: The activity of massive cerebral circuits that have reproducible neuronal signatures.” These unique neuronal signatures can be recognized by brain imaging or electric signals—indeed, they can sometimes be reproduced through direct electrical stimulation of the brain during neurosurgery—as Dehaene makes clear. 

In contrast, if consciousness did not “happen,” much of what we strive for wouldn’t be worth the bother, for there would be no real pain and no real pleasure. Furthermore, it is clear that consciousness does not automatically arise from the presence of complex neurological machinery alone: When we are in a dreamless sleep, under general anesthesia, in a coma, or—like Terri Schiavo—in a “persistent vegetative state,” the light can go off entirely, sometimes forever. Is the light “on” in the brain of an octopus, or are these creatures, as Chalmers might describe, simply eight-legged zombies?

Godfrey-Smith explores the issue from many angles, beginning with a succinct and thoughtful discussion of the evolution of animals, and extending to a look at the octopus’ remarkable neurological systems. His book includes vivid descriptions of the unique capacities of the animal (for instance, the anatomy and physiology by which they change the color of their skin at will), and includes apt discussions of the ideas of consciousness of Dehaene and others. And throughout, Godfrey-Smith intertwines his own keen work observing and filming these animals at a remarkable site off of the coast of Australia he calls “Octopolis.”

He emphasizes a critical point: We vertebrates diverged from the cephalopods a very long time ago, at a “fork” in the evolutionary tree, maybe around 600 million years ago. The complex brains of octopuses, and other cephalopods (e.g. the squid and cuttlefish), thus evolved separate from, or rather, in parallel to, ours. Thus, he writes, “if we want to understand other minds, the minds of cephalopods are the most other of all.”

One fascinating aspect of the “minds” of these animals is their decentralized design: A single nervous system suffuses both head and legs. Indeed, the interface between their brain and body, Godfrey-Smith argues, is not so clear: It surely has a brain (interestingly, its esophagus actually passes through it), but its nervous system runs through the entirety of its body and into its tentacles, each of which have a certain “mental” autonomy. This autonomy has the effect of “freeing the central control from the complex task of directly controlling arm behavior,” as a 2015 study by Guy Levy and colleagues in Current Biology puts it (the study was previously covered by the New York Times). 

Yet the octopus’s arms show us the limits of equating autonomous neurological complexity with consciousness. Consider, for instance, the nervous system of the human gut. This “enteric nervous system,” as it is called, is a fabulously intricate, autonomous, and presumably fully unconscious network of nerves and ganglia interfacing with various muscles, which—by squeezing and relaxing—ensure peristalsis through each unique segment of the alimentary canal. Our brains are thus largely “freed” from the task of the voluntary—or for that matter involuntary—control of this organ system, allowing us, for instance, to enjoy a postprandial nap without micromanaging our digestive activities. It seems safe to assume that—similar to an octopus’ tentacle—our gut does not, as a result, have an independent conscious existence emerging from this network of neurons (which is no doubt a good thing: Imagine what a dull existence it would be, forever trapped in the confines of somebody else’s abdominal cavity, perpetually propelling food and waste!).                               

Additionally, a great deal of complex mental activity can also occur in the brain without us being conscious of it, as Dehaene convincingly surveys in Consciousness and the Brain. He describes a body of work (some of it his own) that demonstrates that a complex array of cognitive activities—including recognition and processing of words or images—can be entirely confined to the subconscious, and which fail to produce the “neuronal signature,” and subjective experience, of consciousness. “Freud was right:”, he states, “consciousness is overrated.”                                                     

A fair point, but perhaps a bit too strongly worded: Consciousness can never be overrated, if only because it is the very thing that makes our lives worth living. A perpetual coma is not so different than death, while life as a sunflower would be—it is true!—entirely stress-free, yet also devoid of a sense of the sun’s warmth. 

But when does the complexity of an animal’s brain reach such a state as to produce a conscious existence? Godfrey-Smith draws a rather subtle distinction between the overall view of consciousness of Dehaene and others in his camp—he calls their perspective the “latecomer view” (meaning that they believe consciousness arose late in evolution, although at least Dahaene has written that consciousness of some sort may have “emerged a long time ago”)—and his own, which he calls the “transformation view.” The work of Dehaene and colleagues has culminated in a theory of consciousness they call the “global neuronal workspace.” Essentially, this workspace serves as a central focus where information can be integrated and united from throughout the brain, for just as long as it is needed. According to this framework, “consciousness is just brain-wide information sharing,” Dehaene writes. Godfrey-Smith has a somewhat different perspective: He sees the “latecomer view” as overly binary, or as too closely tied with the mammalian brain, and instead, suggests a picture of “gradual change,” in which consciousness is “not an all-or-nothing matter,” but instead, emerged slowly and gradually over evolutionary time, until it ultimately “transformed what it feels like to be an animal.”

Notably, in implicit recognition of the possibility that even lowly animals like octopuses may have consciousness, some, particularly in Europe, have moved to classify the octopus as a “honorary vertebrate” in laboratory research, Godfrey-Smith notes. Octopuses could previously be operated on without anesthetic, he says; they could have their nerves cut or might be shocked with electricity, or have pieces of their brains removed “just to see what the octopus would do when it woke up.”

If they were nothing other than eight-legged zombies, this would all be perfectly ethical—no different than the vivisection of a vivacious sunflower. But we risk the possibility that they are not. 

Perhaps we can ultimately be entirely sure only of the consciousness of a single organism: Our self. When we look at other human beings around us—awake and alert and, like us, responsive to beauty, pain, and desire—we rightly assume that, they too have an inner mental existence: Not to do so would be utter madness.

When we stare into the eyes—or study the brain—of an octopus, we are similarly trying to divine whether it too has that spark, or whether it is a zombie, though an elegant and complex one at that. But perhaps the “spark” is in fact an inappropriate metaphor, and that we should instead envision consciousness as a slowly-burning flame—one that burns more brightly in some creatures than in others, that dims in the stupor of profound intoxication, that can be forever quenched by a terrible cerebral injury, and that roars to life anew each time we emerge from a dreamless slumber.