Of all the animals in the sea, few have surprised scientists as much as the…

Of all the animals in the sea, few have surprised scientists as much as the octopus. With no bones and a body that seems almost alien, it is a relative of snails and clams. Yet it has shown problem-solving abilities that would impress us in many mammals.

Even its basic biology is unusual. An octopus has three hearts: two pump blood through the gills, and the third pumps it around the rest of the body. Its blood is blue, because it uses a copper-based molecule rather than the iron-based one found in our own blood to carry oxygen. And its nervous system is organised very differently from ours. An octopus has around 500 million nerve cells, roughly as many as a dog, but about two-thirds of them are located in its eight arms rather than in its central brain. Each arm can therefore react to its surroundings partly on its own, tasting and touching objects as it explores.

Octopuses are also masters of disguise. Special cells in their skin allow them to change colour and pattern in a fraction of a second, and some species can even change the texture of their skin to resemble rocks or seaweed. Remarkably, they do this even though they are thought to be colour-blind.

Their intelligence shows in many ways. In aquariums, octopuses have learned to open jars to reach food inside, and some have escaped from their tanks by squeezing through tiny gaps, since the only hard part of their body is their beak. In the wild, a species called the veined octopus has been filmed carrying coconut shells across the sea floor and assembling them into a shelter, one of the clearest examples of tool use among invertebrates.

Strangely, all this intelligence is packed into a very short life. Most octopuses live only one or two years, and females usually die soon after their eggs hatch, having stopped eating while guarding them. Because young octopuses never meet their parents, everything they know must be learned alone.

Scientists are still debating why such a short-lived, solitary animal should have evolved such complex abilities. One theory is that losing the protective shell of its ancestors forced the octopus to rely on intelligence and flexibility to survive. Whatever the reason, the octopus offers a fascinating glimpse of how intelligence might develop along a completely different path from our own.