How Many Brains Does a Creature Need?

Leeches have 32 brains. Well, sort of. Each of its separate segments contains its own neuronal ganglion. As one answer on Quora puts it, "precisely it does not have 32 brains but a single brain that exists in 32 parts throughout the body," yet because each ganglion works independently, we might say it literally has a brain for each segment.

Is It True That a Leech Has 32 Brains?

Here's a page with thirteen wild and wonderful facts about animal brains:

13 Facts About Animals' Brains

Starfish have their neurons distributed through their arms instead of concentrated in a central location. A spider's brain is too big for its head and extends into its legs. Octopuses, similarly, keep two-thirds of their neurons in their tentacles instead of in the central brain. Thus, like spiders, they can perform amazingly complex feats with their limbs. The octopus, in fact, has the highest brain-to-body mass ratio of any invertebrate. This article explores octopus intelligence, including their ability to use tools:

How Smart Are Octopuses?

On the other hand, although we consider ourselves the planet's superior life form because of our intelligence, the humble sea squirt doesn't appear to value brainpower very highly. In the transition from its immature, mobile phase into an adult rooted in one spot, it "eats" its own brain. Among other animals that seem to consider brains optional, a cockroach can survive a long time with no head (until it starves to death). Then there's the famous case of a chicken named Mike, who lived for eighteen months after being (mostly) decapitated:

Mike the Headless Chicken

So maybe we members of the species Homo sapiens ("wise human") should be a bit more modest about the power to rule Earth through our intelligence? Maybe alien visitors would single out ants or termites as the dominant species, since there are so many more of them than us, and their excavations produce significant effects on the landscape. Or how about grasses? Not only do they cover much of the globe, they obviously employ us as their servants to help them spread and thrive.

Margaret L. Carter

Carter's Crypt