Natural selection.

Darwin formed his hypothesis of natural selection by drawing two inferences based on his observations.

  1. Observation #1 : Individuals of a population exhibit variation in their traits.

  2. Observation #2 : Many traits are heritable.

  3. Observation #3 : Many species overproduce offspring.

  4. Observation #4 : Resources are limited; many of these offspring do not survive due to competition for those resources.

  1. Inference #1 (natural selection): Individuals whose traits give them a high probability of surviving and reproducing are likely to leave more offspring than others.

  2. Inference #2 (adaptation): A population will accumulate favorable traits over generations and become adapted to its environment.