This book is a revised version of a series of Gifford Lectures given at Aberdeen in 1985. The lectures were given under the title “In Praise of Diversity,” which gave me license to talk about everything in the universe. Half of the lectures were about the diversity of the natural world, and half were about the diversity of human reactions to it. The title is now changed so as to focus more sharply upon the message I am preaching. Boiled down to one sentence, my message is the unbounded prodigality of life and the consequent unboundedness of human destiny. As a working hypothesis to explain the riddle of our existence, I propose that our universe is the most interesting of all possible universes, and our fate as human beings is to make it so.

The most substantial change from the Aberdeen text is the omission of a large part of three lectures concerned with the origin of life. Those three lectures were too technical for the Gifford audience and were a rehash of a set of Tarner Lectures given earlier in the same year at Cambridge. The Tarner Lectures have meanwhile been published by the Cambridge University Press in a little book with the title Origins of Life. The Gifford Lectures 3, 4 and 5 appear here in a briefer and less technical version. At various other places in this book, the lectures have been rearranged and supplemented with later writings. Wherever I have used earlier published materials, full acknowledgments are made in the bibliographical notes at the end of the book.

I am grateful to my editors Michael and Cornelia Bessie for their encouragement and help in preparing this work for publication, to my critics Clara Park and Alice Dyson for improving it, to my secretary Paula Bozzay for typing and retyping the manuscript, and to the Institute for Advanced Study at Princeton for tolerating my extracurricular activities.

I am grateful above all to my hosts at the University of Aberdeen for bringing me to their proud city and providing me with a faithful audience. Under a gray sky with incessant wind and intermittent rain and snow, the city was ablaze with daffodils in April and with roses in November. With nothing but a few fishing villages and oil platforms between us and the North Pole, the spirit of the eighteenth-century Scottish Enlightenment still flourished. In spite of my strange mixture of biochemical, astronomical and military jargon, the lecture hall stayed full.