Are big brains smarter?

Asked by: Alan Blackwood, by email

To some extent, yes. Across many species the ratio of brain to body weight is a good predictor of intelligence. In fish the ratio is 1:5000, in birds 1:220, in most mammals 1:180 and in humans 1:50.

MRI brain scans reveal a moderate, but consistent correlation between size and IQ among humans of the same sex. But there are cases of small or damaged brains with high IQs so the rule is not rigid.

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