Armed but Not Dangerous: Is the Octopus Really the Invertebrate Intellect of the Undersea World?

By Stewart, Doug | National Wildlife, February-March 1997 | Go to article overview

Armed but Not Dangerous: Is the Octopus Really the Invertebrate Intellect of the Undersea World?


Stewart, Doug, National Wildlife


Is the octopus really the invertebrate intellect of the undersea world?

Frequently, we humans look down on invertebrates as inferior forms of life. But at least one invertebrate, the octopus, may possess enough brainpower to alter this biological prejudice.

Octopuses are mollusks, like snails, clams and oysters, but they are smarter, nimbler, more curious and more resourceful than any oyster. They have to be: Like their fellow cephalopods, squid and cuttlefish, they lost their external shells millions of years ago, but what they lack in armor, experts say, they make up for in brains. The central nervous system of the octopus is among the largest and most complex in the invertebrate world, rivaling that of many vertebrates, including birds and fish. How intelligent that nervous system makes the octopus is still a matter of scientific debate, however.

Over the years, scientists have tested octopus intelligence by teaching captive specimens to slither through simple mazes and to tell squares from crosses. Octopuses even learn to unscrew lids to get at food.

The most dramatic evidence for octopus intelligence came in 1992. A pair of researchers in Naples, Italy, Graziano Fiorito and Pietro Scotto, used conventional means--food as a carrot, mild electric shock as the stick--to train a group of captive common octopuses to grab a red ball instead of a white one. The scientists then let untrained animals watch from adjoining tanks as their experienced confreres reached for red balls over and over. Thereafter, Fiorito and Scotto reported, most of the watchers, when offered a choice, pounced on red balls. In fact, they learned to do so more quickly than had the original group. The octopuses, according to the researchers, were doing something invertebrate had never been known to do before: learning by watching.

Or so it seemed. Critics since then have weighed in with a list of complaints about the experiment. Controls were sloppy: Fiorito and Scotto themselves concede that untrained octopuses at the outset already preferred red balls by more than three to one. Gerald Biederman of the University of Toronto's Learning Laboratory wrote that octopuses typically "are reluctant to attack novel stimuli." Having watched trained octopuses repeatedly snatch the red ball, the untrained animals may simply have gotten used to watching that ball and so were more apt to pounce on it themselves.

What perplexed scientists most about Fiorito and Scotto's paper, however, was the assumption that the animals would do something in captivity that they would never do in nature. An ability to learn by watching makes sense, in evolutionary terms, only for animals that live in social groups. But octopuses do not.

Indeed, an octopus leads a remarkably solitary life. It never knows its parents. In most species, the mother stops eating while brooding her eggs and dies almost as soon as they hatch. Newborn common octopuses, flealike creatures the size of rice grains, spend their first weeks as ocean plankton, drifting at the surface. After gaining weight, they drop to the bottom, where they spend most of their lives hiding watchfully in dens, which can be rocky crevices, abandoned shells, holes scooped in the sand, even the odd oil drum or mayonnaise jar.

From 150 to 200 species of octopus inhabit the world's oceans. The common octopus, the species best known to scientists, thrives in warm rocky shallows off the coasts of the southeastern United States, western Central America and Japan, as well as in the Mediterranean and the Caribbean. It can weigh up to 50 pounds and have a 10-foot arm span. The species that comes closest in size to the monsters of science fiction is the giant Pacific octopus, found off the western coast of North America and across the northern Pacific to Japan. The biggest ever captured weighed more than 600 pounds and measured 31 feet from arm tip to arm tip. Despite their impressive growth, Pacific giants rarely live longer than three years.

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Armed but Not Dangerous: Is the Octopus Really the Invertebrate Intellect of the Undersea World?
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