In the spirit of Voltaire--and occasionally in the spirit of P. G. Wodehouse--P. B. and J. S. Medawar have crafted for the life sciences a source of reference that is meant for browsing, a book both authoritative and filled with delights. The authors' breadth of knowledge is encyclopedic-- arranged, appropriately enough, from A to Z--but more than that, they illuminate the ideas of biology with wit and intelligence and uncommon good sense. They...