Natural selection is survival of the fittest, those who can adapt to the environment to survive pass on the allele that helps the other generation survive. The three types of natural selection are stabilizing, disruptive, and directional. Stabalizing means the environment supports the medium trait. Disruptive selection is when the environment supports the extremes of the population, directional selection is when the environment supports only one extreme in the population. There are different ways to study evidence of evolution. For example, fossils, geography, comparative anatomy, and molecular biology. Fossils show how current organisms changed from their ancestors.