Other Minds: The Octopus and the Evolution of Intelligent Life

by Peter Godfrey-Smith

An example is quorum sensing. If a chemical is both produced and sensed by a particular kind of bacterium, it can be used by those bacteria to assess how many individuals of the same kind are around. By doing this, they can work out whether enough bacteria are nearby for it to be worthwhile to produce a chemical that does its job only if many cells make it at once. An early case of quorum sensing to be uncovered involves – appropriately for this book – the sea and a cephalopod. Bacteria living inside a Hawaiian squid produce light by a chemical reaction, but only if enough other bacteria are around to join in. The bacteria control their illumination by detecting the local concentration of an “inducer” molecule, which is made by the bacteria and gives each individual a sense of how many potential light producers are around. As well as lighting up, the bacteria follow the rule that the more of this chemical you sense, the more you make. When enough light is being produced, the squid who house the bacteria gain the benefit of camouflage. This is because they hunt at night, when moonlight would normally cast their body’s shadow down to predators below. Their internal lights cancel the shadow. Meanwhile, the bacteria seem to benefit from the hospitable living quarters provided by the squid.

The chemistry of life is an aquatic chemistry. We can get by on land only by carrying a huge amount of salt water around with us.

This chemical influence is the residue of ancient signaling between organisms, pressed inward. The action potential, too, existed in cells before animals evolved, and exists today outside them. The first one ever measured, in fact, was in a plant, the Venus flytrap, at the instigation of Charles Darwin in the nineteenth century. Even some single-celled organisms have action potentials. What nervous systems make

In an animal like us, a large proportion of the energy taken in as food, nearly a quarter in our case, is spent just keeping the brain running.

The bilaterian body plan makes for mobility (walking is a very bilateral thing to do), and this body plan is friendly, it turns out, to many kinds of complex behavior. The diversification and entanglement of

two dozen sophisticated eyes – eyes with lenses and retinas, like ours. The Cubozoa can swim at about three knots, and some can navigate by watching external landmarks on the shore. Box jellyfish, the lethal behavioral pinnacle of non-bilaterian evolution, are also products of the new world that began in the Cambrian.

In the Ediacaran, other animals might be there around you, without being especially relevant. In the Cambrian, each animal becomes an important part of the environment of others. This entanglement of one life in another, and its evolutionary consequences, is due to behavior and the mechanisms controlling it. From this point on, the mind evolved in response to other minds. When

Slow-moving grazers wander over the mats, consuming this rather uniform resource. Other animals feed without moving. These animals then become a new kind of resource; they are big concentrations of nutritious carbon compounds. Nutrition is now less spread out than it was. It exists in patches. These animals might first have only been consumed by others after they had died. But this soon changed. Scavenging became predation. If the fossil record is taken at face value,

One nervous system evolves on the top, and tracks light, but not as a guide to action. Instead it uses light to control bodily rhythms and regulate hormones. Another nervous system evolves to control movement, initially just the movement of the mouth. And at some stage, the two systems begin to move within the body, coming into new relations with each other.

What an amazing image: in a long evolutionary process, a motion-controlling brain marches up through your head to meet there some light-sensitive organs, which become eyes.

Absolute size is important, but it is usually regarded as less informative than relative size – the size of the brain as a fraction of the size of the body. This tells us how much an animal is “investing” in its brain.

Octopuses and other cephalopods have exceptionally good eyes, and these are eyes built on the same general design as ours. Two experiments in the evolution of large nervous systems landed on similar ways of seeing.

On reaching the end of the row, she walked back the way she’d come. The octopus in the first tank, though, seemed to be waiting for her. It had not eaten its squid, but instead was holding it conspicuously. As Boal stood there, the octopus made its way slowly across the tank toward the outflow pipe, watching her all the way. When it reached the outflow pipe, still watching her, it dumped the scrap of squid down the drain.

They are smart in the sense of being curious and flexible; they are adventurous, opportunistic. With this idea on the table I can add more to

If an octopus eats something sharp which pierces the side of its “throat,” the sharp object goes straight into its brain. Octopuses have been discovered with exactly this problem. Further, much of a

But an octopus has three hearts, not one. Their hearts pump blood that is blue-green, using copper as the oxygen-carrying molecule instead of the iron which makes our blood red. Then, of course, there is the nervous system – large like ours, but built on a different design, with a different set of relationships between body and brain.

To use an older term, if it feels like something to be a squid or octopus, then these are sentient beings. Sentience comes before consciousness. Where does sentience come from?

An earthworm withdraws when something touches it – the touch might be a threat. But every time the worm crawls forward, it causes part of its body to be touched in just the same way. If it withdrew at every touch, it could never move at all. The worm succeeds in moving forward by canceling the effects of those self-produced touches. For all organisms there

The pigeons were trained to do a simple task with one eye masked, then each pigeon was tested on the same task while being forced to use the other eye. In a study using nine birds, eight of them did not show any “inter-ocular transfer” at all. What seemed to be a skill learned by the whole bird was in fact available to only half the bird; the other half had no idea.

The special kind of mental fragmentation seen in split-brain humans seems to be a routine part of many animals’ life. Animals seem to have

The weaving gaze of a bird is a technique designed to slosh the incoming information around.

One path to this view begins with an accident, a case of carbon monoxide poisoning from a shower’s bad water heater in 1988, which led to a case of brain damage in a woman known only as “DF.” As a result of the accident, DF felt almost blind. She lost all experience of the shapes and layout of objects in her visual field. Only vague patches of color remained. Despite this, it turned out that she could still act quite effectively toward the objects in space around her. For example, she could post letters through a slot that was placed at various different angles. But she could not describe the angle of the slot, or indicate it by pointing. As far as subjective experience goes, she couldn’t see the slot at all, but the letter reliably went in.

The ventral stream, which takes a lower path through the brain, is concerned with categorization, recognition, and description of objects. The dorsal stream, which runs above it, closer to the top of the head, is concerned with real-time navigation through space (avoiding obstacles as you walk, getting the letter through the slot).

The senses can do their basic work, and actions can be produced, with all this happening “in silence” as far as the organism’s experience is concerned. Then, at some stage in evolution, extra capacities appear that do give rise to subjective experience: the sensory streams are brought together, an “internal model” of the world arises, and there’s a recognition of time and self.

Let’s consider some analogies with our case, beginning with acts like blinking and breathing. These are activities that normally happen involuntarily, but through attention you can assert control over them. An octopus’s arm movements have something like this combination.

In the case of humans, these rapid adjustments of the arm come from the brain, and they are visually guided. In the octopus, the motions are guided by the arm’s own chemical and tactile senses, not by vision (though I’ll qualify that statement in the next chapter; the issue