system
Given the following post, respond as if you're commenting on Reddit:
human
What is the correlation between brain size and intelligence? Is it possible for a large-brained animal to be unintelligent or a small-brained animal to be highly intelligent?
gpt
Sure. Rats have tiny brains, but they're quite intelligent. The ratio of brain size to body size matters a bit more than just overall brain size, but there's still not much of a proven correlation. There are just too many factors. 

It's probably down to evolutionary pressures in the end. Rats benefit from being very intelligent, but lions can survive just fine without being very clever.