"SUPER" BRAIN 30% LARGER THAN A HUMAN'S
On the outside, the Starchild Skull is about the same size as a 12 year old child, or a very small adult. At this size the brain should be about 1,200 cubic centimeters. A larger adult can have a brain as big as 1,400 cubic centimeters. The Starchild has a brain of 1,600 cubic centimeters, a full 30% larger than it should be.
Experts have ruled out any sort of internal pressure in the skull, so we know that the size of the brain cavity is accurate, it hasn't been exaggerated by a medical condition that causes swelling, or anything like that. This is a genuine "super brain," with the sections of the brain devoted to problem solving and sensory perception especially enlarged.
The brain was also shaped quite differently from ours. The images on this page show brain casts made by taking a CT scan of the skull and then creating a cast of the inside surface. You can see from the human control that it gives a very clear indication of the size and shape of the brain. However, the Starchild's brain cast is smoother and strangely shaped. This is accurate, and this is as close to how its brain would have looked as the human cast is to how a human brain looks. The inescapable fact is simply that the Starchild had a very strange brain, one unlike anything else on Earth.