There are not two cultures, Sir Gavin says in the introduction to this collection of essays, book reviews, and lectures. Rather there are streams of culture in which men of science and men of letters at any time share basic mental processes and whatever constitutes the ""creative imagination."" De Beer unites several streams in his own life, having written distinguished works on zoology, Darwin, evolution, the romantic poets, archaeology, and mountain climbing. The majority of essays in the current work deal with evolution past and present: the origin of Darwin's ideas, the union of Mendelian genetics and Darwinian theory, the concepts of ""mosaic"" evolution in which parts of an organism may undergo evolutionary changes independently of other parts. Unfortunately collections of previously published works tend to repeat the author's favorite analogies or examples, so that the reader is told at least three times that Darwin overemphasized the impact of Malthus on his work, that Sir Ronald Fisher's statistical analysis of Mendel's results shows inconsistencies with probability theory, etc. Much of this is of scholarly rather than general interest. The last essays are more speculative and current: an interesting observation about the Rh blood factor in relation to European population genetics; the possibility that Atlantis was the Minoan Empire destroyed by the eruption of a volcano on an island 60 miles north of Crete, and a survey of the medieval documents such as the Vinland map which give strong evidence for Norse settlements in the New World in the good old pre-Columbian days.