How did Charles Lyell's principles of geology influence Darwin's theory of evolution?

• A. Lyell's principles emphasized the fixity of species, contradicting Darwin's ideas.
• B. Lyell's principles supported the idea of spontaneous generation, which Darwin ignored.
• C. Lyell's principles were based on the idea of a young Earth, which Darwin disputed.
• D. Lyell's principles introduced the concept of gradual change, which Darwin applied to biological evolution.

Answer: (D)