This collection of essays demonstrates the width of Darwin's interests and ability as a biologist. The theory of evolution by natural selection was, of course, his most important achievement and is covered in three of the essays: Wilkie presents Darwin's theory in its historical setting and relates it to the earlier work by Buffon and Lamarck; Haldane discusses the theory of evolution by natural selection, as postulated by Darwin, and assesses its validity in the light of subsequent research; and Challinor considers the apparent discrepancy between some of the fossil evidence and Darwin's theory, a problem which Darwin himself appreciated and discussed in The Origin of Species. The other essays deal with subjects about which Darwin wrote separate books. The essay by Bell is concerned with the movement of plants in response to light; that by Marler with communication between animals and that by Whitehouse with cross- and self-fertilization in plants.