Which combination of scientific ideas most directly helped Darwin develop the theory of evolution by natural selection?

• A. Earth’s geological features formed rapidly, and species never became extinct
• B. Species were individually created in their present form, and Earth was unchanging
• C. Fossils represented mythical organisms, and geological change was unrelated to biology
• D. Earth changed gradually over long periods of time, and fossil evidence showed that life had changed through extinction

Answer: (D)