Charles Darwin’s position on the subject of heredity is not the easiest of tasks to establish. Not only was he working on the subject in the shadow of Lamarck’s well-known version of the inheritance of acquired characters, but his own views were crucially shaped by what to him were the more important elements in the mechanism he was formulating for the transmutation of species. He never wrote a book specifically on heredity. In his Origin of Species there is not even a chapter so entitled. How unlike his cousin Francis Galton, who was to write several books on the subject, and the philosopher Herbert Spencer, who introduced to British biologists the term “heredity” in chapter 8 of his Principles of Biology (1864, vol. 1). Compare this with Darwin’s treatment of variation. This topic is the subject of three chapters of the Origin – the first, second, and fifth. Six years later Darwin published his magnum opus, the two-volume Variation of Animals and Plants under Domestication. Here variation is the theme, but this time three chapters are included on heredity: chapter 12 on inheritance, 13 on reversion, and 14 on fixedness of character. Related topics are in chapter 17 on effects of crossing and 19 on hybridism. Of the remaining twenty-five chapters, one is given to his hypothesis of pangenesis, this being Darwin’s attempt at a hypothesis that brings together heredity, variation, and other aspects of the broad field of “generation.”

As for manuscripts, we find in his Transmutation Notebooks beginning in 1837 frequent notes of sources on inheritance, and his discussion of these sources can be found in the chapters on variation in the Origin. The nature of heredity was evidently of considerable concern to him from the early notebooks right on to pangenesis in 1868. How, then, are we to understand Darwin’s study and theorizing on heredity in relation to his work as an evolutionist? Was it a “subfield” that he explored “more with an eye to formulating evolutionary explanations than to solving the internal problems of the field” (Glick and Kohn 1996, 47)? If so, we may be able to identify ways in which he exploited and interpreted selected data in his efforts to find a viable hypothesis for the transmutation of species. For if species are to evolve, variations not only must occur but must be heritable, and the strength of that heritability must be lasting.