[Eli5] what’s the meaning of the ratio brain size/body mass? Why a bigger brain isn’t alone a sign of bigger intelligence? What has body mass to do with it?

Question

[Eli5] what’s the meaning of the ratio brain size/body mass? Why a bigger brain isn’t alone a sign of bigger intelligence? What has body mass to do with it?

In: Biology

Answer 1

A lot of the brain’s computing power is consumed on more mundane tasks like motor function and organ monitoring and sensory input processing.

Bigger animals have more sheer mass to them and more cells that need to communicate with the brain, so their brains are generally larger by simple necessity. A sperm whale has a brain several times larger than a human but they’re not out there doing calculus – most of that space is consumed with the functions of their gigantic body and very little is reserved for higher-order processing.

Humans have a big brain and a relatively compact and spindly body, we’ve dedicated a relatively large amount of physical brain space to thinking about stuff.