This work set forth Lawrence's then radical and remarkably advanced ideas concerning evolution and heredity. Arguing that theology and metaphysics had no place in science, Lawrence relied instead on empirical evidence in his examination of variation in animals and man, and the dissemination of variation through inheritance. On the question of cause, Lawrence disagreed with those who ascribed variation to external factors such as climate, and rejected the Lamarckian notion of the inheritance of acquired characteristics. His understanding of the mechanics of heredity was well ahead of his time: he stated that "offspring inherit only [their parents'] connate qualities and not any of the acquired qualities," and that the "signal diversities which constitute differences of race in animals . . . can only be explained by two principles . . . namely, the occasional production of an offspring with different characters from those of the parents, as a native or congenital variety; and the propagation of such varieties by generation" (p. 510). While Lawrence did not grasp the role that natural selection plays in the origination of new species, he recognized that "selections and exclusions," including geographical separation, were the means of change and adaptation in all animals, including humans. He noted that men as well as animals can be improved by selective breeding, and pointed out that sexual selection was responsible for enhancing the beauty of the aristocracy:

"The great and noble have generally had it more in their power than others to select the beauty of nations in marriage; and thus . . . they have distinguished their order, as much by elegant proportions of person, as by its prerogatives in society" (p. 454) Lawrence investigated the human races in detail, and insisted that the proper approach to this study was a zoological one, since the question of variation in mankind "cannot be settled from the Jewish Scriptures; nor from other historical records" (p. 243). The Natural History of Man came under fire from conservatives and clergy for its materialist approach to human life, and Lawrence was accused of atheism for having dared to challenge the relevance of Scripture to science. In 1822 the Court of Chancery ruled the Natural History blasphemous, thus revoking the work's copyright. Lawrence was forced to withdraw the book; however, it continued to be republished in unauthorized editiions. Darwin , who owned one of the unauthorized editions, cited Lawrence's book five times in The Descent of Man (1871)