Octopuses are invertebrates, animals without a backbone, yet they are among the most intelligent creatures in the sea. An octopus about five neurons, and two thirds of are in its . arm can taste, and even make simple on its own.

Octopuses can change the color and texture of their skin in less than a second. Their skin thousands of special filled with , which they with their . , most octopuses to be color-blind, scientists still to understand how they match their surroundings so well.

Octopuses have long fascinated scientists because their intelligence evolved along a completely separate path from ours. The last common ancestor of humans and octopuses lived more than 500 million years ago and was probably a simple, worm-like creature. Whatever intelligence octopuses have, they developed it independently.

In laboratories, octopuses have learned to find their way through mazes, unscrew jar lids to reach food and recognize individual human caretakers, sometimes squirting water at people they seem to dislike. In aquariums, some have escaped from their tanks. In 2016, an octopus named Inky made headlines after slipping out of his tank at the National Aquarium of New Zealand and apparently escaping through a drainpipe into the sea.

Their nervous system is also unusual. Most of an octopus’s neurons are located not in its central brain but in its arms, which can respond to touch and taste with considerable independence.

Some researchers suggest that octopus intelligence may be linked to their bodies. With no shell to protect them, octopuses must solve problems quickly to find food and avoid predators.

One of the great puzzles of octopus biology is how short their lives are. Many species live for only one or two years. In most animals, large brains are found in long-lived, social species, such as elephants, dolphins and humans, which have time to learn from experience and from one another.

Octopuses break this pattern. Most live alone, and many females die soon after their eggs hatch, so young octopuses never meet their parents. Everything they know, they must learn by themselves, and quickly.

Scientists have proposed several explanations. One possibility is that the intense pressure of predators made rapid learning valuable, even over a short life. Another idea links the short lifespan to reproduction: in many species, a female stops eating while guarding her eggs, and her body declines rapidly afterward.

Whatever the reason, octopuses challenge a long-held assumption in biology: that intelligence develops mainly in animals that live long lives in social groups.