Life on earth is inseparably linked to evolution, and nearly all scientists, especially biologists, accept evolution as fact. Evolution is the idea that living things have changed over time. Extinction is one way life on Earth can change.
Biologists also agree that natural selection exists and that it contributes to evolution.
Individuals whose inherited genetic characteristics fit them best to their environment are likely to leave more offspring than those that do not fit as well. For example, one species of moth has both white forms and black forms. For the most part, white forms beget white young and black forms beget black young. The color difference between them is heritable, that is, based on their genes. The black form had a selective advantage over the white form because the black form could hide from predators on the blackened trees more easily than the white form could.