[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 large portion of the brain is devoted to keeping the body alive and doing background tasks, not just intelligence and conscious thought. A larger body needs a larger brain: larger muscles farther away due to body size need stronger signals to activate, higher amounts of hormones need to be released since there’s a lot more blood in the body to dilute them, bigger sensory organs need more processing power (bigger eyes, for example, have more photoreceptors and provide more data to the brain), etc.