Octopus Fact File : Six Extra Arms But No Sixth Sense!!!

Racing snails, with guts through their brains……

In his beautiful book ‘Other Minds: the octopus and the evolution of intelligent life’, Peter Godfrey-Smith describes the extraordinary convergent evolution of problem-solving intelligence in animals. 2020’s Academy Award winning documentary by Craig Foster ‘My Octopus Teacher’ spectacularly illustrates that intelligence in action.

There are over 300 species of octopus, and the group separated from the vampire-squids (and other squid) over 150 million years ago. By contrast, apes only split from the old-world monkeys about 25 million years ago and the whole primate group originated no more than 80 million years ago, so octopus have been around about twice as long as primates. How come they haven’t taken over the world?

There are two clear problems for octopus.

Firstly, their guts run through their brains. Technically they have a circum-oesophageal brain. Literally, whenever they swallow, the food passes between the optic-lobes and through the ring-shaped nerve masses of the brain. Weirdly, but perhaps obvious given how they live, octopus typically have more neurons in their arms than in their brains, but with 8 arms, and those arms being highly independent in their actions, perhaps that isn’t so surprising. The big gap in the middle of their brain means that integration is a problem and nerve pathways are necessarily long (and therefore slow).

Secondly, octopus are racing snails. They are molluscs that have specialised in a very high-speed lifestyle. Most octopus are seasonal and live for just one year. Even giant pacific octopus only live for 4-5 years. They live fast, produce huge numbers of offspring, put all their energy into producing those offspring, and die before or shortly after their offspring hatch. There is no time for octopus to learn. The young are independent as soon as they are born. There is no opportunity for adults to teach the young – no parental care – no overlap of generations to allow cultural information to pass from one generation to the next.

Image: Coconut Octopus hunting for prey on the sea floor
Image: Coconut Octopus hunting for prey on the sea floor

Finally, though, there has been speculation that octopus haven’t taken over the world because they are exclusively marine, and animals underwater are never going to discover fire, so they will never develop technology. I’m not at all convinced by that argument. Fire has been key to our technology, allowing protection from predators, and the ability to modify materials by fusing, melting and chemical alterations. All of those things are impossible underwater, but other things are much easier – particularly electrical signalling. Many marine (and freshwater) animals are able to detect the electrical signals given off by muscles and neurons, and some use those signals for direct communication. Others – such as electric eels – use self-generated electric signals to directly take-over the muscles of their prey and force them to swim puppet-fashion out of their hiding-places and into the predator’s mouth. Perhaps underwater intelligences would bypass fire entirely and go straight to electronics and IT.

A final thought on octopus intelligence: years ago, I worked with Martin Wells, grandson of H.G. Wells, and long-term Octopus researcher (he had a side-interest in dragonflies). He did tests on octopus to see whether they could tell the difference between different shapes by touch, and whether they could transfer that information to vision. They could reach out and feel an object and count the number of corners, so they could distinguish between a star, a square and a triangle because they have 3, 4 and 5 corners – and they could feel the sharp bits. But to an octopus a pentagon and a 5-pointed star are the same. They can’t feel the indentations between the points because they have no way to measure the angles their arms take up, the length, or the curvature of their arms. They completely lack proprioception – the 6th sense that tells us where our limbs are and allows us to accurately reach out and touch a target – they have to feel their way to it. Our proprioceptive sense helps us accurately use tools, everything from a spear to a smartphone, so maybe this lack of proprioception and absence of culture is why octopus, for all their remarkable abilities, haven’t taken over the world just yet.