Natural Selection

Summary of Darwin's Theory of Evolution

A species is a population of organisms that interbreeds and has fertile offspring.

Living organisms have descended with modifications from species that lived before them.

Natural selection explains how this evolution has happened:

More organisms are produced than can survive because of limited resources

Organisms struggle for the necessities of life; there is competition for resources.

Individuals within a population vary in their traits; some of these traits are heritable -- passed on to offspring.

Some variants are better adapted to survive and reproduce under local conditions than others.

Better-adapted individuals (the "fit enough") are more likely to survive and reproduce, thereby passing on copies of their genes to the next generation.

Species whose individuals are best adapted survive; others become extinct