Facts and Inferences That Define Natural Selection

The theory proposed by Charles Darwin was not a theory for evolution, but a theory explaining the mechanism by which evolution occurred.

Natural Selection . A theory that states that a population of organisms can change over time as a result of individuals with certain heritable traits leaving more offspring than other individuals

Facts and Inferences that Define Natural Selection

Fact 1: There is a potential exponential increase of population; populations grow very quickly. (Malthus) Fact 2: Population sizes are relatively stable. (Naturalists) Fact 3: Resources are limited. (Malthus) Inference 1: There is a struggle for existence. (Malthus) Fact 4: Individuals are unique. (Breeders and Taxonomists) Fact 5: Many characteristics are inherited. (Breeders) Inference 2: There is differential survival if a trait helps an individual to survive and reproduce. It might be passed on to the next generation.  Natural Selection (Darwin) Fact 6: The earth is very old. (Lyell) Inference 3: Through many generations new species evolve  Survival of the fittest. (Darwin)

Darwin summarized natural selection in these words...”Can we doubt (remembering that more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and procreating their kind? On the other hand, we may feel that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable variations and the rejections of injurious variations I call Natural Selection.”