and what is all that extra brain capacity for?
It's actually a myth that we only use 10% or some other small percentage of our brains. In fact most of our brain is active at all times, though some parts fire up and generate more heat while working on a problem, and we can see this in realtime brain scans. But there's no "cold spots" where the brain just isn't doing anything.
JWs perpetuate the 10% myth in public talks because it meshes with their belief that we are imperfect and not functioning at full capacity. People who promote woo also like this myth because it implies that there are mystery areas in the brain that might allow telekinesis, telepathy, etc. The myth probably came from a newspaper writer in the early 20th century who misunderstood the finding that the brain's gray cells are outnumbered by white cells ten to one.
The gray cells do the thinking, so this would imply that the rest of the brain is unused, but in fact the white matter connects the areas of the brain, so it's crucial to have. Men have more gray cells than women as a percentage of their brain mass, but this means that women have a higher ratio of white matter, which confers its own benefits.
Even without there being a massive untapped portion of the brain, it's amazing what we can do with training, thanks to neuroplasticity. And some people are "mutants" who employ a different section of the brain to perform a task than an ordinary person does, like Scott Flansburg, the human calculator. So there's lots of fascinating scientific facts out there without these pseudo-science shows that make scientists look bad.
