Noted linguist William Foley claims that language developed when brain size in the evolving humans took an upward leap.1 As brains grew larger, their complexity of neural connections became very much greater and language became possible.
But really it is not brain size that matters, but how that brain is organized.
Brain size in humans ranges widely, typically somewhere between 1040_ml and 1595 ml.2 Even though brain size tends to correlate with body size, it would be simplistic and false to say that a large person with a 1500_ml brain should be nearly twice as intelligent as a pygmy with a 900_ml brain!
People of all body sizes have potentially the same mental abilities, simply because they are human. It's true that some have a higher IQ than others. That's part of the ordinary variability between individuals. But IQ does not correlate with the physical size of the brain.3•