Abstract

The “long argument” presented in the opening chapter of On the Origin of Species develops steadily. Darwin’s comparison between variation under domestication (Chapter I) and variation under nature (Chapter II) is an argument that approximates artificial and natural selection, rendering the second more intelligible. However, questions remain about whether Darwin conceived the analogy before developing the theory of natural selection or whether its use later fulfilled a didactic strategy. Despite not being part of the book, Darwin’s theory of inheritance, Pangenesis, is fundamental for understanding the chapter. Darwin himself recognised that the origin and inheritance of variation were probably the book’s most uncertain subject: “The laws that govern inheritance are quite unknown”. However, with his ancient concept of inheritance, it becomes clear that in the development of evolutionary thinking, it was the very existence of variation and not its origin that mattered.