Here's the Australian Aboriginal skull vs the European Aryan's skull. Their skulls don't even have the volume capacity to house our brains even if we could do a brain transplant. They, and many other negroid races retain something called the Simian Shelf, which is prevalent in primates and is a plate at the position of the frontal lobe that fuses at 10-12yr old that prevents its ability to grow. This is the region that houses the brain's neocortex which is the part of the brain responsible for abstraction and reasoning ability.