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.