I'm not convinced that's a complete argument. Rather there's a fix point: The brain is adapt at increasing its size. That's what everything does: Growing. The

I'm not convinced that's a complete argument. Rather there's a fix point: The brain is adapt at increasing its size. That's what everything does: Growing. The brain is just especially good at it. The advantage also manifests in the "schema of childlike characteristics" (Kindchenschema) which includes a big head. So it's evidently also important for affection on a different level: child care and protection. There are pretty bold statements in your comment, that may be countered with a lack of constraints on the growth. Intelligence affords fitness in myriads of ways, of course.