This is a book for people who love and understand science and want to know more about contemporary research frontiers. The questions addressed are as fascinating as they are diverse: Is the human mind truly unique among the primates? Does "dark matter" really exist in the universe? What can the human genome tell us about our evolutionary history? These wide-ranging topics are brought together by virtue of their impact on our understanding of ourselves--and by the caliber of the authors: ten young scientists and scholars, reaching the height of their powers, who are especially talented in communicating their research findings to broad audiences. They were chosen to receive the prestigious Centennial Fellowships awarded in 1998 by the McDonnell Foundation, established and funded by the late aerospace pioneer James S. McDonnell.