4.2: Other Mechanisms of Evolution

BIOL 101- Environmental Science · LibreTexts

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    Other Sources of Evolutionary Change

    Natural selection is the primary mechanism discussed in this chapter, but populations can also change through other evolutionary processes.

    Mutation

    A mutation is a change in DNA. Mutations create new genetic variation within populations and are the ultimate source of new inherited traits.

    Most mutations have little or no effect on an organism. Some are harmful, while others may be beneficial under certain environmental conditions.

    Without mutation, new genetic variation would not arise, and natural selection would have less variation to act upon.

    Genetic Drift

    Genetic drift is a random change in the genetic makeup of a population caused by chance events (figure \(\PageIndex{a}\). Genetic drift has the greatest effect in small populations. For example, a wildfire, flood, or disease outbreak may randomly eliminate individuals regardless of their traits. As a result, some genetic variation may be lost simply by chance.

    Small populations often have lower genetic diversity and may be more vulnerable to environmental change. This is one reason conservation biologists are concerned about endangered species with small populations.

    Bottleneck effect reduces diversity as only a few individuals survive.
    Figure \(\PageIndex{a}\): A chance event or catastrophe can reduce the genetic variability within a population.

     

    Gene Flow

    Gene flow occurs when individuals move into or out of a population and bring their genes with them (figure \(\PageIndex{b}\)). For example, seeds may be dispersed by wind, animals may migrate between habitats, or pollen may be carried long distances. Gene flow can increase genetic diversity and introduce new traits into a population.  

    A brown beetle moves into a green beetle population, introducing new genes (gene flow).
    Figure \(\PageIndex{b}\): Gene flow can occur when an individual travels from one geographic location to another and joins a different population of the species. In the example shown here, the brown allele is introduced into the green population.

    Summary

    Natural selection is not the only process that causes populations to change over time. Mutation introduces new genetic variation, genetic drift changes populations through chance events, and gene flow moves genetic variation between populations.

    Together with natural selection, these processes influence how populations respond to environmental change.

     

    Attributions

    Modified by Erin Rempala. 

    This page titled 4.2: Other Mechanisms of Evolution was last modified on Mon, 27 Jul 2026 19:49:29 GMT and is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by OpenStax.