For decades now, I have been haunted by the grainy, black-and-white x-ray of a human skull.
It is alive but empty, with a cavernous fluid-filled space where the brain should be. A thin layer of brain tissue lines that cavity like an amniotic sac. The image hails from a 1980 review article in Science: Roger Lewin, the author, reports that the patient in question had “virtually no brain”. But that’s not what scared me; hydrocephalus is nothing new, and it takes more to creep out this ex-biologist than a picture of Ventricles Gone Wild.
What scared me was the fact that this virtually brain-free patient had an IQ of 126.
Briefly, a hypothesis.
Most of the volume of your brain consists of white matter: a fatty substance the texture of semi-firm tofu, composed of glia, myelin, and the long tails of axons further up in the brain. It can tolerate a fair amount of damage before causing serious effects: as we age, its volume shrinks considerably without affecting IQ, and although diffuse white-matter injuries can have horrifying effects, small ischemic strokes can take chunks out of it without the patient noticing.
Most of what's missing in this guy is white matter.
But even if you're completely lacking white matter, there's a second route between parts of the brain: across the surface of the grey matter. In most anatomically normal people, the routes across the surface of the brain are fairly slow and unreliable, as they only directly interconnect adjacent parts of the brain. But presuming that whatever deprived him of most of his white matter didn't impair axon recruitment between lobes -- and it looks like it might not have, as one of the few interior structures that's still intact is the corpus callosum -- it's possible that his brain is simply more space-efficient than the rest of Homo sapiens.
Which did not, I might remind you, undergo a design review process to prove that its brain is constructed efficiently.