Why do octopuses have such large brains?

But why do they have such a highly developed brain in the first place? Scientists usually attribute large brains in animals to social behaviour: if an animal needs to live in a group, recognise its fellow creatures, compete, cooperate and learn from one another, its brain becomes larger.

This logic doesn’t really apply to octopuses. Many of them live solitary lives. A new study suggests that cephalopods may have developed large brains not because of social interaction, but because of the complex and dangerous environment in which they must constantly search for food, hide and make quick decisions.

The paper has been published in iScience; a version of the study is also available as open access on bioRxiv.

Details

The researchers analysed data on 79 species of cephalopods — octopuses, squids and cuttlefish. They compared brain size with lifestyle, habitat, depth, behaviour and level of sociality.

The result was unexpected: in cephalopods, brain size was better explained by environmental conditions than by social behaviour. Species living closer to the seabed and in more complex environments tended to have larger brains. Species from the deep sea or the open ocean, on average, had smaller brains.

Put simply: the more complex the environment in which an animal lives, the more challenges it has to overcome.

Why habitat is so important

An octopus living amongst rocks, reefs, hiding places and predators must constantly make decisions. Where to hide? Where is the prey? How to open a shell? How to evade a predator? How to change colour to blend into the background?

In the open ocean, there may be fewer such ‘puzzles’. The environment there is more uniform: fewer hiding places, fewer complex surfaces, fewer opportunities to use objects or hide in crevices.

Therefore, the brains of bottom-dwelling species may have grown larger not because they needed to communicate, but because they needed to survive in a complex world.

Octopuses are solitary creatures, but not simple ones

Many intelligent animals are social. For example, primates, dolphins, elephants and crows live in complex social systems. Consequently, the idea that a large brain evolved primarily for communication and group living was long held.

Octopuses defy this pattern. They often live alone, do not form long-term social bonds and do not have complex group hierarchies, unlike monkeys or dolphins. Yet they display complex behaviour: they learn, remember, explore objects, change hunting strategies and use camouflage.

The authors of the study believe that cephalopods demonstrate a different path to intelligence: not through society, but through the environment. This idea is known as the ‘asocial brain’ hypothesis. It suggests that a large brain can develop even in solitary animals, provided the surrounding world is sufficiently complex and rewards the ability to learn.

In simple terms: why does an octopus need a large brain?

An octopus needs to do more than just swim and eat. It needs to constantly solve practical problems.

It must find prey that is hiding.

It must hide from predators itself.

It must quickly change its body colour and shape.

They must remember where their hiding places are.

It must work out how to extract food from a shell, a crevice or a carapace.

Such a way of life requires flexibility. And flexibility requires a complex nervous system.

Why this discovery is important

The research shows that intelligence in animals may have emerged through different pathways. In some species, the brain grew larger as a result of social life. In others, it was due to a complex environment, hunting, hiding places, predators and the need to solve problems quickly.

This is important because octopuses, squid and cuttlefish are evolutionarily very distant from humans. Their lineage diverged from that of vertebrates hundreds of millions of years ago. If they, too, have developed large brains and complex behaviour, it means that nature can ‘invent’ intelligence in different ways.

In other words, octopuses did not become intelligent by following the same path as humans, apes or dolphins. They found their own way.

Background

Scientists have long been fascinated by octopuses because their nervous system is unusually structured. A significant proportion of their neurons are found not only in their ‘head’ but also in their tentacles. This enables an octopus’s tentacles to perform complex movements and react to the world around them with great flexibility.

That is why octopuses seem almost like aliens amongst marine animals. They do not look like us, do not live like us, do not think like us — yet they still solve complex problems.

New research adds an important insight to this picture: a large brain may develop not only where there is a social structure, but also where the environment itself presents animals with difficult challenges on a daily basis.

Source

Study: Kiran Basava et al., “Ecological not social factors explain brain size in cephalopods”, iScience, 2026.