Octopuses have large nervous systems, centered around relatively large brains. But more than half of their 500 million neurons are found in the arms themselves, Godfrey-Smith said. This raises the question of whether the arms have something like minds of their own. Though the question is controversial, there is some observational evidence indicating that it could be so, he said. When an octopus is in an unfamiliar tank with food in the middle, some arms seem to crowd into the corner seeking safety while others seem to pull the animal toward the food, Godfrey-Smith explained, as if the creature is literally of two minds about the situation.

There may be other explanations for the observations. But whatever the answer, it seems likely that octopus intelligence is quite different from that of humans and, as researchers ponder the broader meaning of intelligence, may be as different as is likely to be encountered, short of finding it on other planets.

That’s because other creatures that are believed intelligent — such as dolphins, chimpanzees, some birds, elephants — are relatively closely related to humans. They’re all on the vertebrate branch of the tree of life, so there’s a chance the intelligence shares at least some characteristics. Octopuses, however, are invertebrates. Our last common ancestor reaches back to the dim depths of time, 500 million to 600 million years ago. That means octopus intelligence likely evolved entirely separately and could be very different from that of vertebrates.