The octopus has a most remarkable nervous system that allows it to solve challenging problems, such as how to escape from a glass jar closed with a screw top.
However, when octopuses were given a transparent jar that contained a live crayfish, they failed to do anything. This greatly puzzled the scientists, because the delicacy was clearly visible and moving about. Do octopuses perhaps have trouble unscrewing a lid from the outside? It turned out to be one of those human misjudgments. Despite having excellent eyes, octopuses rarely rely on vision to catch prey. They use mainly touch and chemical information and fail to recognize prey without those cues. As soon as the jar was smeared on the outside with herring “slime,” making it taste like fish, the octopus swung into action and started manipulating it until the top came off. It quickly removed the crayfish and ate it. With further skill development, the process became routine.21
In captivity, octopuses react to us in ways that we find hard not to anthropomorphize. One octopus was fond of raw chicken eggs—each day it would accept an egg and break it to suck out its contents. One day, however, this octopus accidentally received a rotten egg. Upon noticing, it shot the egg’s smelly remains over the edge of its tank back at the surprised human from whom it had received it.22 Given how well they distinguish people, octopuses probably remember encounters like these. In a recognition test, an octopus was exposed to two different persons, one of whom consistently fed it, whereas the other mildly poked it with a bristle on a stick. Initially, the animal made no distinction, but after several days it began doing so despite the fact that both humans wore identical blue overalls. Seeing the loathsome person, the octopus would withdraw, emit jets of water with its funnel, and show a dark bar through its eyes—a color change associated with threat and irritation. It would approach the nice person, on the other hand, without making any attempt at drenching her.23
The octopus brain is the largest and most complex of all invertebrates, but the explanation of its extraordinary skills may lie elsewhere. These animals literally think outside the box. Each octopus has nearly two thousand suckers, every single one equipped with its own ganglion with half a million neurons. That amounts to a lot of neurons on top of a 65-million-neuron brain. In addition, it has a chain of ganglia along its arms. The brain connects with all these “mini brains,” which are also joined among themselves. Instead of a single central command, as in our species, the cephalopod nervous system is more like the Internet: there is extensive local control. A severed arm may crawl on its own and even pick up food. Similarly, a shrimp or small crab can be handed from one sucker to the next, as if on a conveyer belt, in the direction of the octopus’s mouth. When these animals change skin color in self-defense, the decision may come from central command, but perhaps the skin is involved as well, since cephalopod skin may detect light. It sounds rather unbelievable: an organism with seeing skin and eight independently thinking arms!24
This realization has led to a bit of hype: that the octopus is the most intelligent organism in the ocean, a sentient being that we should stop eating. We shouldn’t overlook dolphins and orcas, though, which have vastly larger brains. Even if the octopus stands out among invertebrates, its tool use is rather limited, and its reaction to a mirror is as perplexed as that of a small songbird. It remains unclear whether an octopus is smarter than most fish, but let me hasten to add that such comparisons barely make any sense. Instead of turning the study of cognition into a contest, we should avoid putting apples next to oranges. The octopus’s senses and anatomy, including its decentralized nervous system, make it unparalleled.
If superlatives of uniqueness were allowed, the octopus might be the most unique species of them all. They defy comparison with any other group, unlike our own species, which derives from a long line of land vertebrates with structurally similar body plans and brains.
Octopuses have an odd life cycle. Most live only one or two years, which is unusual for an animal with their brainpower. They grow fast while trying to stay away from predators until they have a chance to mate and reproduce, after which they die. They stop eating, lose weight, and go into senescence.25 This is the stage about which Aristotle observed: “after giving birth … [they] become stupid, and are not aware of being tossed about in the water, but it is easy to dive and catch them by hand.”26
These short-lived loners have no social organization to speak of. Given their biology, they have no reason to pay attention to one another, except as rivals, mates, predators, and prey. They are certainly not friends or partners. There is no evidence that they learn from others or spread behavioral traditions, the way many vertebrates, including fish, do. The absence of social bonds and cooperation, and their cannibalistic ways, make cephalopods quite alien to us.
Their main worry is predation, because apart from their own kind, they are eaten by almost everything around, from marine mammals, diving birds, sharks, and other fish to humans. When they get larger, they become formidable predators themselves, as the Seattle Aquarium accidentally found out. Worried about their giant Pacific octopus in a tank full of sharks, staff were hoping that the animal would know how to hide. But then they noticed one dogfish (a small shark) after another disappearing from the tank—and found to their astonishment that the octopus had turned the tables. The octopus may be the only playful invertebrate. I say may since play behavior is almost impossible to define, but the octopus appears to go beyond mere manipulation and checking out of novel objects. The Canadian biologist Jennifer Mather found that given a new toy, the animal will move from exploration (“What is this?”) to repeated lively movements and tossing around (“What can I do with it?”). With their funnel, they blow jets of water at a floating plastic bottle, for example, to move it from one side of their tank to another, or to have it tossed back at them by the water flow of the filter, which makes them look as if they were bouncing a ball. Such manipulations, which serve no obvious purpose and are repeated over and over, have been taken as indications of play.27