Why do humans have such a long period of childhood compared to other mammals? Why is our species becoming less aggressive and more reserved? Why is speech unique to humans? And, most importantly, why is our brain getting smaller and smaller? Bruce Good, a professor at Harvard and Cambridge, reveals to readers the fascinating world of psychology and neurobiology. In an accessible and entertaining way, the author helps to understand the mysteries of our brain and makes it possible to understand what exactly makes us who we are - human beings.