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How Smart Is the Octopus?Bright enough to do the moving-rock trick.
By Carl Zimmer
Updated Monday, June 23, 2008, at 1:14 PM ET


Aristotle didn't have a high opinion of the octopus. "The octopus is a stupid creature," he wrote, "for it will approach a man's hand if it be lowered in the water." Twenty-four centuries later, this "stupid" creature is enjoying a much better reputation. YouTube is loaded with evidence of what some might call octopus intelligence. One does an uncanny impression of a flounder. Another mimics coral before darting away from a pushy camera. A third slips its arms around a jar, unscrews it, and dines on the crab inside. Scientific journals publish research papers on octopus learning, octopus personality, octopus memory. Now the octopus has even made it into the pages of the journal Consciousness and Cognition (along with its fellow cephalopods the squid and the cuttlefish). The title: "Cephalopod consciousness: behavioral evidence."

So, is the octopus really all that smart? It depends on how you define intelligence. And if you've got a good definition, there are quite a few scientists who would love to hear it. Octopuses can learn, they can process complex information in their heads, and they can behave in equally complex ways. But it would be a mistake to try to give octopuses an IQ score. They are not intelligent in the way we areā€”not because they're dumb but because their behavior is the product of hundreds of millions of years of evolution under radically different conditions than the ones under which our own brains evolved.

You'd have to go back about 700 million years to find the moment in the history of life when humans and octopuses diverged. Our most recent common ancestor, scientists suspect, was a little wormlike creature with eyespots and little more. Since then, our lineage evolved bones; theirs evolved boneless bodies they control with water pressure. We've accumulated so many and such incredible differences over that time that 20th-century scientists were excited to discover a few deep similarities. In the 1950s, for example, biologists demonstrated for the first time that octopuses have massive brains.

Cephalopods belong to the same lineage that produced snails, clams, and other mollusks. A typical mollusk might have 20,000 neurons arranged in a diffuse net. The octopus has half a million neurons. The neurons in its head are massed into complex lobes, much the way our own brains are. In comparison with their body weight, octopuses have the biggest brains of all invertebrates. They're even bigger than the brains of fish and amphibians, putting them on par with those of birds and mammals.

In the late 1950s, Oxford biologist N.S. Sutherland decided to put the big brains of octopuses to the test. He would show them two shapes and reward them for touching one but not the other. They might learn to tell a rectangle in a horizontal position from the same rectangle rotated 90 degrees. And once they had figured out this test, the octopuses knew to select any horizontal rectangle they saw, no matter what its particular dimensions. They were learning what to learn.

Over the years, octopuses have shown many more signs of intelligence. They proved to have an excellent memory. They were clever and unpredictable. Jennifer Mather, a Canadian biologist, has tossed toys into octopus tanks and watched as the octopuses inspect them and puff them around with jets of air. They are playing, she argues. Clams do not play. Humans do.