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

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СКАЧАТЬ scale (far from it), and doesn’t represent actual descent relations between species. It presents a chronological sequence of forms seen in cephalopod evolution from over half a billion years ago to the present, with a few of the most important branchings marked along the way. I have included the controversial Kimberella as a possible early stage. The capped limpet-like shellfish is a monoplacophoran. The next animal, with a shell divided into compartments, is something like Tannuella. Opinion seems divided on whether the next in line, Plectronoceras, had lifted off the ground or was still on the sea floor, but this animal is often regarded as the first “true” cephalopod, because of various internal features. Cameroceras is the giant of the large predatory cephalopods, with conservative length estimates of up to eighteen feet. The octopus and squid are descended from unknown cephalopods that gave up their external shells and are now extinct, unlike the nautilus, which kept its shell and lived on. Figure by Eliza Jewett.

      ~ Puzzles of Octopus Intelligence

      As the cephalopod body evolved toward its present-day forms, another transformation occurred: some of the cephalopods became smart.

      “Smart” is a contentious term to use, so let’s begin cautiously. First, these animals evolved large nervous systems, including large brains. Large in what sense? A common octopus (Octopus vulgaris) has about 500 million neurons in its body. That’s a lot by almost any standard. Humans have many more – something like 100 billion – but the octopus is in the same range as various smaller mammals, close to the range of dogs, and cephalopods have much larger nervous systems than all other invertebrates.

      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. This comparison is made by weight, and only counts the neurons in the brain. Octopuses also score high by this measure, roughly in the range of vertebrates, though not as high as mammals. Biologists regard all these assessments of size, though, as only a very rough guide to the brainpower an animal has. Some brains are organized differently from others, with more or fewer synapses, and those synapses can also be more or less complicated. The most startling finding in recent work on animal intelligence is how smart some birds are, especially parrots and crows. Birds have quite small brains in absolute terms, but very high-powered ones.

      When we try to compare one animal’s brainpower with another’s, we also run into the fact that there is no single scale on which intelligence can be sensibly measured. Different animals are good at different things, as makes sense given the different lives they live. An analogy can be drawn with tool kits: brains are like tool kits for the control of behavior. As with human tool kits, there are some elements in common across many trades, but much diversity also. All the tool kits found in animals include some kind of perception, though different animals have very different ways of taking in information. All (or almost all) bilaterian animals have some form of memory and a means for learning, enabling past experiences to be brought to bear on the present. The tool kit sometimes includes capacities for problem solving and planning. Some tool kits are more elaborate and expensive than others, but they can be sophisticated in different ways. One animal might have better senses, while another may have more sophisticated learning. Different tool kits go with different ways of making a living.

      When comparing cephalopods with mammals, the difficulties are acute. 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. But the nervous systems beneath those eyes are organized very differently. When biologists look at a bird, a mammal, even a fish, they are able to map many parts of one animal’s brain onto another’s. Vertebrate brains all have a common architecture. When vertebrate brains are compared to octopus brains, all bets – or rather, all mappings – are off. There is no part-by-part correspondence between the parts of their brains and ours. Indeed, octopuses have not even collected the majority of their neurons inside their brains; most of the neurons are found in their arms. Given all this, the way to work out how smart octopuses are is to look at what they can do.

      Here we quickly encounter puzzles. Perhaps the heart of the matter is a mismatch between the results of laboratory experiments on learning and intelligence, on one side, and a range of anecdotes and one-off reports, on the other. Mismatches like this are common in the world of animal psychology, but they are especially acute in the case of octopuses.

      When tested in the lab, octopuses have done fairly well, without showing themselves to be Einsteins. They can learn to navigate simple mazes. They can use visual cues to determine which of two possible environments they have been placed in, and then take the correct route to a goal for that environment. They can learn to unscrew jars to obtain the food inside. But octopuses are slow learners in all these contexts. When you read the fine print of a “successful” experiment, progress often seems agonizingly slow. Against a background of mixed experimental results, though, there are anecdotes suggesting that a lot more is going on. What I find most intriguing is the octopus’s ability to adapt to new and unusual circumstances – confinement in a lab – and turn the apparatus around them to their own octopodean purposes.

      A lot of early octopus work was done in Italy, at the Naples Zoological Station, in the middle of the twentieth century. Peter Dews was a Harvard scientist who worked mostly on the interaction between drugs and behavior. He had a general interest in learning, though, and his octopus experiment did not involve drugs at all. Dews was influenced by his Harvard colleague B. F. Skinner, whose work on “operant conditioning” – the learning of behaviors by reward and punishment – had revolutionized psychology. The idea that successful behaviors will be repeated and unsuccessful ones abandoned had been pioneered by Edward Thorndike around 1900, but Skinner developed the idea in great detail. Dews, with many others, was inspired by the way Skinner was able to make animal experiments rigorous and exact.

      In 1959 Dews applied some standard experiments on learning and reinforcement to octopuses. Octopuses may be distantly related to vertebrates like us, but do they learn in similar ways? Can they learn, for example, that pulling and releasing a lever will get them a reward, and come to produce this behavior at will?

      I first came across Dews’s work through a brief mention of his experiment in Roger Hanlon and John Messenger’s book Cephalopod Behaviour. Hanlon and Messenger comment that pulling and releasing a lever is surely something an octopus would never do in the sea, and they say that Dews’s experiment was not successful. I was curious about how things went, though, so I went back to the 1959 paper. The first thing I noticed is that the experiment was successful with respect to its main goals. Dews trained three octopuses, and found that all three of them did learn to operate the lever to obtain food. When they pulled the lever, a light came on and a small piece of sardine was given as a reward. Two of the octopuses, named Albert and Bertram, did this in a “reasonably consistent” manner, Dews said. The behavior of the third octopus, named Charles, was different. Though Charles did pass the test in a minimal way, his handling of the situation encapsulates much of the story with octopus behavior. Dews wrote:

      1. Whereas Albert and Bertram gently operated the lever while free-floating, Charles anchored several tentacles on the side of the tank and others around the lever and applied great force. The lever was bent a number of times, and on the 11th day was broken, leading to a premature termination of the experiment.

      2. The light, suspended a little above the level of the water, was not the subject of much “attention” by Albert or Bertram; but Charles repeatedly encircled the lamp with tentacles and applied considerable force, tending to carry the light into the tank. This behavior is obviously incompatible with lever-pulling behavior.

      3. Charles had a high tendency to direct jets of water out of the tank; specifically, they were in the direction of the experimenter. The animal spent much time with eyes above the surface of the water, directing СКАЧАТЬ