I think its correlation vs causation kind of. Brain-to-body size how important the brain is for the animal. A big animal can have a big brain, because why not.

I think its correlation vs causation kind of. Brain-to-body size how important the brain is for the animal. A big animal can have a big brain, because why not. But for a small animal to have a big brain it means a certain sacrifice. This shows how much emphasis evolution has put on the brain. More emphasis leads to bigger brains, but more importantly to smarter wiring.