Consists of selected excerpts from previous writing by Professor Simpson - without any doubt the most eminent of all evolutionary biologists. Each of the six sections begins with a general statement about the subjects to be covered. Each separate text is preceded by a comment, the purpose of which is to provide background and context for the following text and also, when appropriate, to discuss the present status of the subject. Thus although the book is centred on papers previously published, its comments are new and in sum present a current viewpoint on the subjects treated