What was Darwin's greatest contribution to evolutionary theory?

Darwin's greatest contribution to evolutionary theory lies in his ideas about natural selection. He proposed that individuals within a species exhibit variation in traits, and these variations can affect their ability to survive and reproduce. Natural selection is the process by which advantageous traits become more common in a population over generations, leading to adaptation to the environment.

This concept fundamentally shifted the understanding of how species evolve over time, emphasizing that it is not random but rather a gradual process influenced by environmental pressures. Darwin's insights into natural selection laid the groundwork for modern evolutionary biology, connecting diverse fields such as genetics, ecology, and paleontology. This framework is crucial for understanding how species adapt and evolve, making it the cornerstone of evolutionary theory.

In contrast, other contributions, such as fossil comparisons or classifications based on morphology, while important, do not encapsulate the mechanism of evolution as effectively as the theory of natural selection does. It's this conceptual leap that has allowed for a deeper understanding of biodiversity and the history of life on Earth.