One of Earth's Most Extraordinary Creatures
If you were designing an intelligent creature from scratch, you probably wouldn't give it three hearts, nine brains, and blood that runs blue through its veins. Yet that's exactly what evolution produced when it shaped the octopus — one of the most biologically remarkable animals on the planet.
Far from being a quirk of nature, every strange feature of octopus anatomy serves a precise, functional purpose. Understanding why these creatures are built the way they are reveals a lot about how life adapts to extreme environments.
The Three-Heart System Explained
An octopus has three hearts, each with a distinct job:
- Two branchial hearts sit at the base of each gill. Their sole purpose is to pump deoxygenated blood through the gills, where it picks up oxygen from the water.
- One systemic heart (the main heart) then pumps the now-oxygenated blood out to the rest of the body — the organs, muscles, and skin.
This division of labor exists because of a key limitation: when the main systemic heart pumps blood to the body, it loses enough pressure that a single heart couldn't efficiently push blood through the gills and the body simultaneously. Having dedicated gill hearts solves this problem elegantly.
There's a fascinating trade-off, though. When an octopus swims by jet propulsion — squirting water to propel itself — the systemic heart actually stops beating temporarily. This is why octopuses tire quickly when swimming and prefer crawling along the seabed. Their cardiovascular system simply wasn't optimized for sustained open-water travel.
Why Is Octopus Blood Blue?
Human blood is red because it uses hemoglobin — an iron-based protein — to carry oxygen. Octopus blood uses a completely different molecule: hemocyanin, which is copper-based. When copper binds to oxygen, it turns blue.
Hemocyanin is actually less efficient than hemoglobin at carrying oxygen under normal conditions. But it has a significant advantage in cold, low-oxygen environments — like the deep ocean — where it outperforms hemoglobin at releasing oxygen to tissues. Evolution tailored octopus blood chemistry to the specific conditions where they thrive.
Nine Brains: Distributed Intelligence
An octopus doesn't have nine separate brains in the traditional sense. More accurately, it has one central brain plus eight semi-autonomous neural clusters — one in each arm. About two-thirds of an octopus's total neurons are located in its arms, not its central brain.
This means each arm can:
- Respond to touch and obstacles independently
- Execute complex movements without waiting for central brain commands
- Solve simple problems (like opening a jar) semi-automatically
Even a severed octopus arm will continue reacting to stimuli for up to an hour. The central brain sets goals and intentions, but the arms largely figure out the execution on their own — a form of distributed intelligence unlike anything found in vertebrate animals.
Three Fun Facts to Take Away
- Octopuses have short lifespans — most species live only 1–2 years, which makes their demonstrated intelligence all the more remarkable.
- Their pupils are rectangular, which may help them detect polarized light — useful for spotting prey that would be invisible to other predators.
- Despite being colorblind, octopuses can match color and texture in their skin with extraordinary precision, likely using light-sensitive proteins in their skin itself.
What This Tells Us About Evolution
The octopus is a powerful reminder that intelligence and complexity can evolve along entirely different paths. Vertebrates and cephalopods share a common ancestor that lived roughly 600 million years ago — a simple, eyeless worm-like creature. Everything that makes an octopus remarkable evolved independently from the line that produced fish, birds, mammals, and us.
That's not just a fascinating fact. It's a window into how many different solutions nature can find to the same problems of survival.