Why do leeches need 32 brains?


Just saw that they have 32 brains and curious why something so small needs so many brains.

In: 43

They don’t really have 32 brains, just each segment of their body is locally controlled, enabling fast response times to a stimulus. Like in humans the distance between the knee and the brain is considerable and a response might take a second to a stimulus so we short circuit some reactions with a reflex reaction.

Leeches are build up of modular and fairly similar segments (with the segments near each end being more specialized).

If they have 32 brains or not depends on how you look at it. Another way of looking at it is that have 1 brain-structure with 32 segments spread out along the nervecord (which fulfills the same role as the nerves in our spine, they just don’t have any bones around it). Also the segments near the head and near the tail have fused into slightly bigger bundles of braincells.


Their brain is not like our brain. They are just ganglia (our brain is made of millions of ganglia)

They don’t, because they do not really have a brain. They have a bunch of nerve nodes (little masses of nerves). But a brain is really only a node of nerves, a complicated one for sure, and the center of a big network. Animals with small networks and primitive brains are really just a bunch of local nodes that aren’t true brains. We call them “brains” but they really aren’t what most people think of as a brain. They are more than just isolated nerves, but less than a central brain.

The nervous systems of animals is a spectrum, from basically nothing but a few local masses of nerves serving a tiny part of the nervous system, to one big mass serving the entire system, and different levels of complexity in between. Animals with “good” brains still have those simple nodes in the outer reaches of the nervous system. There is just a much larger and more central “brain”. “primitive” animals do not have a central brain. just nodes. haven’t evolved to the point of a central brain.

Kind of the same idea with “hearts”. Things like worms have many “hearts” but they are not true hearts. More like muscular arteries.