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Chapter 3: Introduction to Evolution

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    Learning Objectives
    • Objective 1: Define evolution and explain its central role in biology.
    • Objective 2: Introduce the different mechanisms of evolution, including natural selection, population bottlenecks, and genetic drift.
    • Objective 3: Outline key patterns and processes of adaptive evolution.
    • Objective 4: Explain the issues with common microencephalons about evolution, particularly natural selection.

    • 3.1: Evolution
      All species of living organisms, from bacteria to baboons to blueberries, evolved at some point from a different species. Although it may seem that living things today stay much the same, that is not the case—evolution is an ongoing process.
    • 3.2: Understanding Evolution
      Evolution by natural selection describes a mechanism for how species change over time. That species change had been suggested and debated well before Darwin began to explore this idea. The view that species were static and unchanging was grounded in the writings of Plato, yet there were also ancient Greeks who expressed evolutionary ideas.
    • 3.3: Mechanisms of Evolution
      Four factors that can change the allele frequencies of a population. Natural selection works by selecting for alleles that confer beneficial traits or behaviors, while selecting against those for deleterious qualities. Mutations introduce new alleles into a population. Genetic drift stems from the chance occurrence that some individuals have more offspring than others and results in changes in allele frequencies that are random in direction.
    • 3.4: Adaptive Evolution
      Fitness is often quantifiable and is measured by scientists in the field. However, it is not the absolute fitness of an individual that counts, but rather how it compares to the other organisms in the population. This concept, called relative fitness, allows researchers to determine which individuals are contributing additional offspring to the next generation, and thus, how the population might evolve.
    • 3.5: Common Misconceptions about Evolution
      Although the theory of evolution initially generated some controversy, by 20 years after the publication of On the Origin of Species it was almost universally accepted by biologists, particularly younger biologists. Nevertheless, the theory of evolution is a difficult concept and misconceptions about how it works abound. In addition, there are those that reject it as an explanation for the diversity of life.


    The theory of evolution is the unifying theory of biology, meaning it is the framework within which biologists ask questions about the living world. Its power is that it provides direction for predictions about living things that are borne out in experiment after experiment. The Ukrainian-born American geneticist Theodosius Dobzhansky famously wrote that “nothing makes sense in biology except in the light of evolution". He meant that the tenet that all life has evolved and diversified from a common ancestor is the foundation from which we approach all questions in biology.

    Contributors and Attributions

    • Connie Rye (East Mississippi Community College), Robert Wise (University of Wisconsin, Oshkosh), Vladimir Jurukovski (Suffolk County Community College), Jean DeSaix (University of North Carolina at Chapel Hill), Jung Choi (Georgia Institute of Technology), Yael Avissar (Rhode Island College) among other contributing authors. Original content by OpenStax (CC BY 4.0; Download for free at

    This page titled Chapter 3: Introduction to Evolution is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by OpenStax.

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