Charles Darwin has had more impact on biological sciences, and society generally, than any other 19th century biologist. Yet his modus operandi as a scientist is poorly known by evolutionists, and often seriously misinterpreted. Two important aspects of his reasoning discussed here are his hypothetico-deductive approach and his search for mechanisms to explain past events. A wide range of statements from his autobiography and letters show that he worked explicitly in the hypothetico-deductive model. The extracts include strong statements that theories were essential even to know what data to collect; to hold theories only as hypotheses; the necessity to search for data that contradict a cherished theory. He also built on the very mechanistic geological tradition of James Hutton and Charles Lyell, and thus brought into historical biology the search for mechanisms that could be studied in the present to explain events in the past. Taken together, the statements show an excellent scientist working effectively on conceptual issues, whilst searching for mechanisms that could be studied in the present and that would have operated in the past. In retrospect, our understanding has been hampered by forcing overly-simplistic binary choices, such as uniformitarianism and catastrophism. It is important, especially in teaching and interactions with the public, that Darwin’s mode of working is better known, and we need to be more proactive in getting across the message that evolution is good testable science.
Mechanisms of evolution, conjectures and falsification, geology, philosophy of science, theoretical biology, role of hypotheses