Brain size vs. body size and the roots of intelligence

Enlarge (credit: Andrew Howe)

Behavior that we'd consider intelligent is oddly widespread in the animal kingdom. Animals with very different brains from ours-a species of octopus and various birds-engage with tools, to give just one example. It seems intuitive that a brain needs a certain level of size and sophistication to enable intelligence. But figuring out why some species seem to have intelligence while closely related ones don't has proven difficult-so difficult that we don't really understand it.

One of the simplest ideas has been that size is everything: have a big enough brain, and you at least have the potential to be smart. But lots of birds seem to be quite intelligent despite small brains-possibly because they cram more neurons into a given volume than other species. Some researchers favor the idea that intelligence comes out of having a large brain relative to your body size, but the evidence there is a bit mixed.

This week, a team of researchers published a paper arguing that the answer is a little of both: relative and absolute size matter when it comes to the brain. And they argue that a specific approach to brain development helps enable it.

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