It's how your brain is wired rather than size that matters.

It's certainly true that Homo sapiens, as a species, have large brains. But what this means is increasingly murky. Evidence from palaeoanthropology suggests that some species, such as the "hobbits" Homo floresiensis and Homo naledi, performed complex behaviours despite having fairly small brains. 

These reports are contentious. However, there is also gathering evidence from genetics and neuroscience that brain size is far from the be-all-and-end-all of intelligence. Instead, changes to the brain's wiring diagram, to the shapes of neurons, and even to when and where certain genes are turned on, are all equally if not more important. Size, as we might have guessed, isn't everything. 

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