Other Minds: The Octopus and the Evolution of Intelligent Life. Peter Godfrey-Smith

just four octopuses, who were not doing much. But I could tell it was an unusual place. There was a bed of scallop shells, as Matt had said, a couple of yards in diameter. It seemed to contain shells of many ages. An encrusted rock-like object, a foot high or so, sat in the middle, with the largest octopus on the site using it as a den. I took measurements and photos, and began coming back whenever I could. Soon I was seeing the high concentrations of octopuses and complex behaviors that Matt had encountered on his first dives there.

      If we had air enough and time, I don’t know how long we’d stay down there. When the site is active, it’s enthralling. The octopuses eye each other from their dens among the shells. They periodically haul themselves out and move over the shell bed or away onto the sand. Some will pass by others without incident, but an octopus might also send out an arm to poke or probe at another. An arm, or two, might come back in response, and this leads sometimes to a settling-down, with each octopus going on its way, but in other cases it prompts a wrestling match.

      The first photo on the next page was taken just off the edge of the site, and it’s to give you a sense of how these animals look. The species is Octopus tetricus, a medium-size octopus found just in Australia and New Zealand. This is a fairly large individual; from the sea floor to the high spot at the end of its back would be a bit under two feet. It is rushing toward another octopus, off to the right.

      The next scene is on the shell bed itself. The octopus on the left is leaping toward the one on the right, who is stretched out and starting to flee.

      Frame from video taken by unmanned cameras (collaboration by Peter Godfrey-Smith, David Scheel, Matt Lawrence and Stefan Linquist).

      And this is a more serious fight, on the sand just off the edge of the site:

      In order to study changes in the shell bed, I once brought out some stakes and hammered them into the sea floor to mark the site’s approximate boundaries. The stakes, about seven inches long, were made of plastic, so I taped a heavy metal bolt to each one to give it more weight. I drove the stakes in so that only an inch or so of each one sat above the sand, and placed them at the four compass points. They’re very inconspicuous, hard to see unless you know exactly where to look. Some months later I went out to the site again, and found that one of the stakes had been hauled out and added to the pile of debris around one of the octopus dens, some distance away. The stake, I think, would have quickly been found inedible, and it was probably not especially useful as a barricade. But as with tape measures, cameras, and many other things we bring down to the site, the stake’s novelty seemed to make it interesting to an octopus.

      Other octopus manipulations of foreign objects are done for more practical reasons. In 2009, a group of researchers in Indonesia were surprised to see octopuses in the wild carrying around pairs of half coconut shells to use as portable shelters. The shells, neatly halved, must have been cut by humans and discarded. The octopuses put them to good use. One half-shell would be nested inside another, and the octopus would carry the pair beneath its body as it “stilt-walked” across the sea bottom. The octopus would then assemble the halves into a sphere with itself inside. A wide range of animals use found objects for shelters (hermit crabs are an example), and some use tools for collecting food (including chimps and some crows). But to assemble and disassemble a “compound” object like this, and put it to use, is very rare. It’s not clear what to compare this behavior to, in fact. Many animals combine a variety of materials when making nests – a lot of nests are “compound” objects. But those are not disassembled, carried around, and put back together.

      The coconut-house behavior illustrates what I see as the distinctive feature of octopus intelligence; it makes clear the way they have become smart animals. 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 my picture of how octopuses fit into the range of animals and the history of life.

      In the previous chapter, using some ideas from Michael Trestman, I said that across the wide range of animal body plans, only three groups contain some species with “complex active bodies.” Those are chordates (like us), arthropods (like insects and crabs), and a small group of mollusks, the cephalopods. The arthropods went down this road first, in the early Cambrian, over 500 million years ago. The way they did this may have initiated a process of evolutionary feedback that soon encompassed everyone else. Arthropods were first, and chordates and cephalopods followed.

      Setting aside our own case, we can see a difference in the paths taken by the two other groups. Many arthropods specialize in social living and coordination. Not all of them do this – indeed, the majority of arthropod species don’t – but in the area of behavior, many of the great arthropod achievements are social. This is seen especially in ant and honeybee colonies, and in the air-conditioned cities built by termites.

      Cephalopods are different. They never went onto land (though some other mollusks did), and while they probably started on the road toward complex behavior at a later date than the arthropods, they eventually evolved larger brains. (Here I think of an ant colony as many organisms with many brains, not as one.) In arthropods, very complex behaviors tend to be achieved through the coordination of many individuals. Some squid are social, but with nothing like the organization of ants and honeybees. Cephalopods, with the partial exception of squid, acquired a non-social form of intelligence. The octopus, most of all, would follow a path of lone idiosyncratic complexity.

      ~ Nervous Evolution

      Let’s look more closely now at what’s inside an octopus, and how the nervous system behind these behaviors evolved.

      The history of large brains has, very roughly, the shape of a letter Y. At the branching center of the Y is the last common ancestor of vertebrates and mollusks. From here, many paths run forward, but I single out two of them, one leading to us and one to cephalopods. What features were present at that early stage, available to be carried forward down both paths? The ancestor at the center of the Y certainly had neurons. It was probably a worm-like creature with a simple nervous system, though. It may have had simple eyes. Its neurons may have been partly bunched together at its front, but there wouldn’t have been much of a brain there. From that stage the evolution of nervous systems proceeds independently in many lines, including two that led to large brains of different design.

      On our lineage, the chordate design emerges, with a cord of nerves down the middle of the animal’s back and a brain at one end. This design is seen in fish, reptiles, birds, and mammals. On the other side, the cephalopods’ side, a different body plan evolved, and a different kind of nervous system. These nervous systems are more distributed