"The question of evolution by the agency of natural selection has now been debated for one whole generation. The result of the battle, so far, has been to concentrate almost the entire interest of the struggle upon the question whether or not the mind of man can have been evolved from the psychical faculties of the lower animals. We have not hesitated to declare, again and again, that such an evolution is necessarily impossible; but our critics and opponents, from Professor Huxley downwards, have evaded, rather than combated, the arguments whereby we supported our position. This book proposes to detail the origin of human reasoning by examining recent hypotheses concerning it."--Chapter 1.