Would it surprise you to learn that our brains have been shrinking for the last 20,000 years? It’s true. In a major reversal from the two million years before that, our brains have actually been growing smaller. We’ve lost about a baseball sized amount of matter in a brain that’s not any bigger than a football. One reason for that is our bodies are smaller as well (except for maybe Shaq), but that only accounts for a small amount of the loss.