A form of natural selection in which the selective advantage of a heritable trait depends on the frequency of that trait in the population.

(1768-1830)
French physicist and mathematician, most famous for creating the mathematical tools to study how heat flows through solids. His studies of heat led him to argue that Earth’s history had a direction, beginning warm and cooling through time — an idea at odds with Lyell’s view of Earth’s history as one of constant, but directionless, change.

Changes in gene frequencies that usually accompany starting a new population from a small number of individuals. The newly founded population is likely to have quite different gene frequencies than the source population because of sampling error (i.e., genetic drift). The newly founded population is also likely to have a less genetic variation than the source population. For a more detailed explanation, see our resource on adaptation in Evolution 101.

All the feeding interactions of predator and prey, along with the exchange of nutrients into and out of the soil. These interactions connect the various members of a community, and describe how energy passes from one organism to another. Also referred to as the “food web.”

A genotype’s success at reproducing (the more offspring the genotype leaves, the higher its fitness). Fitness describes how good a particular genotype is at leaving offspring in the next generation relative to other genotypes. Experiments and observations can allow researchers to estimate a genotype’s fitness, assigning it a numerical value. For a more detailed explanation, see our resource on fitness in Evolution 101.

A trait in which the phenotypic expression of the genotype has been shaped by natural selection such that environmental variation triggers the production of different adaptive phenotypes well-suited to that environment — i.e., a trait with adaptive phenotypic plasticity. For example, melanin level is a facultative trait. Humans that are exposed to higher levels of solar radiation produce more melanin, which provides protection from the sun. This response likely evolved through many generations of natural selection. For more details, see our resource on genotype vs. phenotype in Evolution 101.

Any trace of a living organism (body, part of body, burrow, footprint, etc.) preserved over geologic time.