Table 2 The five major principles of natural selection that are emphasized in the supplement, based on work by Bray Speth et al. (2009)

Variation: Individuals within a population vary in many traits, including physical and biochemical ones.

Inheritance: Some of the differences in traits among individuals can be passed from parents to offspring.

Origin of variation: Some of the variation in traits among individuals has a genetic basis. This variation originated, often many generations ago, as mutations—changes in the genetic information that are random with respect to the needs of the organism.

Fitness: Both the environment and the traits individuals possess affect survival and reproduction. Individuals with heritable traits that enable them to better survive and reproduce in a particular environment will leave more offspring.

Evolutionary change in populations: The frequency of traits and the alleles that affect those traits change in a population over time.