If aliens had designed a creature to make us rethink intelligence, it might look a lot like an octopus. And yet it lives in the sea, and our last common ancestor with it lived more than 500 million years ago.
Three hearts, blue blood
An octopus has three hearts. Two pump blood through the gills, and one sends it to the rest of the body. Its blood is blue because it uses copper-based hemocyanin to carry oxygen, rather than the iron in our haemoglobin.
A brain in every arm
An octopus has around 500 million neurons, and roughly two-thirds of them sit in its arms. Each arm can taste, touch and make basic decisions on its own, which is why a severed arm can still react for a while.
Master of disguise
Specialised skin cells called chromatophores let an octopus change colour and pattern in a fraction of a second. Yet most octopuses are thought to be colour-blind in the usual sense. Scientists are still debating how they match backgrounds so well.
Clever by any measure
Octopuses open jars, escape from tanks, use coconut shells as portable shelters and recognise individual humans. Their intelligence evolved on a completely separate path from ours, which makes them a rare chance to ask what thinking can look like.
A short, intense life
Many species live only one to two years. The mother of some species guards her eggs without eating until they hatch, and dies soon afterwards.
Intelligence has been invented more than once. We just happen to be the ones writing about it.
Next time you see one in a documentary, remember: you are looking at a mind that grew up in a completely different world.
