What octopuses can teach us about minds
A short tour of the strangest cognitive machine on Earth. Select any paragraph and ask the assistant to explain it, rephrase it, or place it in context.
An octopus has roughly five hundred million neurons, about the same as a dog. But the wiring is unlike any vertebrate brain. Two thirds of those neurons live in the arms, not in the central brain. Each arm runs a substantial amount of its own motor planning and sensory integration locally, which is why a severed octopus arm will continue to react to touch and even grab nearby food for several minutes.
Their skin is its own information system. Underneath are millions of pigment cells called chromatophores, each one opened or closed by a tiny ring of muscles. Layered below those are iridophores and leucophores, which scatter or reflect light. Together they let an octopus reproduce the color and texture of a coral, a rock, or a sandy bottom in fractions of a second. The remarkable detail is that octopuses are mostly colorblind, and yet they match colors accurately. The leading hypothesis is that the skin itself has photoreceptors and senses light directly.
Cephalopods edit their RNA at extraordinary rates. Most animals make small, occasional substitutions in messenger RNA before it is translated into protein. Octopuses, squids, and cuttlefish make tens of thousands of edits, and a substantial fraction occur in the genes that build neurons. This may be how they fine-tune neural function in response to temperature without slow generations of natural selection. The trade-off appears to be a much slower rate of underlying genetic evolution.
They solve novel problems. Captive octopuses learn to open screw-top jars, navigate mazes, distinguish individual human caretakers, and remember which ones have been unkind. There is at least one careful study in which an octopus, given a transparent box containing food, opened it the long way around rather than through the obvious flap, suggesting some kind of mental simulation rather than pure trial and error.
Their relationship to time is strange. Most octopus species live one or two years, breed once, and die soon after, in a process driven by hormonal signals from the optic gland. A single animal can therefore acquire a remarkable range of skills, only to lose them on a schedule. From a human standpoint this looks tragic. From an evolutionary standpoint it is simply the cost of investing everything in a brief, intense life.
Studying octopuses tends to widen the definition of mind. They evolved their cognition independently of vertebrates, starting from a common ancestor more than five hundred million years ago, when the most sophisticated neural tissue on the planet was probably a nerve net. Whatever they do with their distributed brains, they arrived at it on a separate evolutionary line. The result is a working example of intelligence built on a different plan, which is exactly the kind of comparison that a single-example field of study most needs.