If the thesis advanced in this book can be corroborated by experiments currently being carried out in a number of laboratories around the world, it will signify an intellectual revolution and a landmark in the history of science. E. J. Steele here suggests that on the basis of his own immunological research, the theory originally put forward by Lamarck 170 years ago and subsequently rejected—the notion that organisms may transmit characters acquired in their lifetimes to their offspring—may in fact be right. In the new postscript to the second edition, Steele presents his latest findings and replies to the enormous body of criticism his research has engendered.