Brain size has roughly tripled in the last 4 million years of human evolution. If the within species correlation between intelligence and brain size is about 0.4, and evolution selected humans to be smart, not big brained per se, then as much as brain size has increased, it arguably increased no more than 40% as much as intelligence has increased because brain size was just a spandrel for intelligence. If a mere by-product of selection for intelligence tripled in size during the last 4 million years, imagine how extreme the direct selection for intelligence was!
So what is it about humans that is so many quantum leaps smarter than chimps? I would say, it’s our ability to ask questions. Chimps can be taught sign language and some can acquire large vocabularies and communicate effectively and be good conversationalists, but they never ever ask a single question. The ability to ask questions is a uniquely human ability. Even babies who speak only a single word can ask questions: “mamma?”
And it’s not because chimps lack curiosity or can’t learn the linguistic skills to ask questions…it’s because…I just figured out why!
In order to ask questions, you have to know that you don’t know. In other words you need meta-knowledge (knowledge about knowledge; knowing you don’t know) and true self-awareness. Self-awareness and the ability to acquire meta knowledge were quantum leaps forward in intelligence, likely associated with the tripling in brain size.
It also explains why talk show hosts are often brilliant. Their job requires them to ask questions: