The earliest human had a brain as small as a child's fist, while ours are four times bigger, with spectacular abilities and potential we are only just beginning to understand. Taking a seven-million-year journey through our own heads, neuroscientist Joseph Jebelli reveals how memory has almost nothing to do with the past, and he carefully considers how the human brain has been—and continues to be—rewired by climate, meditation, autism, and even the use of magic mushrooms.