Quirks & Quarks

The octopus might have traded its shell for intelligence

A new hypothesis suggests intelligence is a "kind of weapon" octopuses use to avoid being eaten.

A new hypothesis suggests intelligence was a 'kind of weapon' octopuses used to avoid being eaten

A two-month-old octopus tries to unscrew the lid of a jar to get hold of its content, a crab, at Denmark's Aquarium in Copenhagen. (JORGEN JESSEN/AFP/Getty Images)

One of the animals that's thought to give creatures like apes, dolphins and crows a run for their money when it comes to intelligence is the octopus. For those other animals, there's a pattern to how they evolved to be so smart — they live long, socially complex lives. But that's not the case for octopuses that live solitary lives for the year or two they usually survive.

Now scientists think they've figured out how the octopus became so so smart, and it has to do with the loss of their shell through evolution. 

"Octopuses, unlike many other molluscs, they do not have a protective shell," said Piero Amodio, the lead author on the new study published in the journal Trends in Ecology & Evolution about how cephalopods (octopuses and their relatives) gained their intelligence.

"So [octopuses] are very, very vulnerable to many kinds of predators — from fishes to marine mammals to birds — and the idea is that by becoming quite smart, this is a kind of weapon they can use to avoid being eaten."

Amodio, a PhD student at the University of Cambridge, told Quirks & Quarks host Bob McDonald that this evolutionary process differs from those that led to intelligence in other groups of vertebrates.

Intelligence in other vertebrates is thought to have arisen because they live long and socially complex lives. Building a brain is a metabolically labour intensive process, so it's a big investment for an animal to develop a big brain like in apes, dolphins, and crows — an investment they get a return on when they live a long time.

How smart are they?

While there isn't a lot of rigorous scientific evidence to explain how smart octopuses really are, Amodio says there's plenty of anecdotal evidence.

It was the middle of the night and no one saw Inky the octopus leave New Zealand's national aquarium, but staff found a trail of water leading from the tank to a 50-metre drainpipe leading to the ocean. (National Aquarium of New Zealand)

In 2016, an octopus named Inky made a daring escape from the national aquarium in New Zealand. The eight-armed Houdini squeezed through a tiny gap a maintenance worker left at the top of its tank.

Inky slithered across the floor and made his escape down a drain pipe that exits into the ocean. That appears to be some clever route-finding, Amodio says. 

A veined octopus hides in an coconut shell. Scientists have filmed the octopus collecting and assembling coconut shells for shelter. (Associated Press/Museum Victoria, Roger Steene)

An octopus was also caught on video camera carrying around two halves of a coconut to hide in whenever it needed to quickly find shelter, he says, adding that on the surface this seems like a smart use of tools.

Other examples, like octopuses opening jars to get at a tasty meal inside, show they poses problem-solving skills, explains Amodio.

There have been some studies on the cuttlefish, an octopus relative, that seem to show its intelligence.

For example, if a cuttlefish is approached by a fish that hunts by sight, the cuttlefish changes colour, showing big black spots that look like eyes.

Cuttlefish are another type of cephalopod that scientists think display intelligence. (YE AUNG THU/AFP/Getty Images)

If it's approached by a different kind of predator, the cuttlefish will just flee the scene.

Amodio says that shows that the cuttlefish behaves differently depending on the type of predator that's after it.

Proving a new route to intelligence

Cephalopod brains, like what octopuses have, are very different than our brains or those of dolphins and crows.

"Two thirds of their neuron cells, they are not located in the brains, but they are located in their arms," Amodio told Quirks & Quarks.

"In octopus, there is a big level of independence of movement for the arms."

While their arms interact with their brains, they can exhibit some movement without the brain sending a signal to the arms, he says.

"It's something completely different from our way of thinking about brains and of course about apes and crows," said Amodio.

To confirm Amodio's theory about how intelligence might have developed due to predation pressures on cephalopods once they lost their protective shell, he says there are two lines of research that could be done.

The first is to scientifically assess how smart cephalopods are compared to other smart animals.

Another approach, according to Amodio, is to compare how big the brains of different cephalopods are in relation to the environment they live in.

"If we would find that cephalopods with bigger brains are the [ones] living in an environment where there is more predators or more different kind of predators, this would suggest that predation played a key role in the evolution of their intelligence," he said. 


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