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5.5: Resources

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    Evolution by natural selection arises from three conditions: individuals within a species vary, some of those variations are heritable, and organisms have more offspring than resources can support. The consequence is that individuals with relatively advantageous variations will be more likely to survive and have higher reproductive rates than those individuals with different traits. The modern synthesis of evolutionary theory grew out of the reconciliation of Darwin’s, Wallace’s, and Mendel’s thoughts on evolution and heredity. Population genetics is a theoretical framework for describing evolutionary change in populations through the change in allele frequencies. Population genetics defines evolution as a change in allele frequency over generations. In the absence of evolutionary forces allele frequencies will not change in a population; this is known as Hardy-Weinberg equilibrium principle. The evidence for evolution is found at all levels of organization in living things and in the extinct species we know about through fossils. Fossils provide evidence for the evolutionary change through now extinct forms that led to modern species. Speciation occurs along two main pathways: geographic separation (allopatric speciation) and through mechanisms that occur within a shared habitat (sympatric speciation). Both pathways force reproductive isolation between populations.

    Review Questions

    1. If a person scatters a handful of plant seeds from one species in an area, how would natural selection work in this situation?
    2. Explain the Hardy-Weinberg principle of equilibrium.
    3. Describe natural selection and give an example of natural selection at work in a population.
    4. Two species of fish had recently undergone sympatric speciation. The males of each species had a different coloring through which females could identify and choose a partner from her own species. After some time, pollution made the lake so cloudy it was hard for females to distinguish colors. What might take place in this situation?
    5. How does the scientific meaning of “theory” differ from the common, everyday meaning of the word?
    6. Explain the following terms: adaptation, bottleneck effect, modern synthesis.


    CK12. (2015). Evidence for evolution. Retrieved from Available under Creative Commons Attribution-NonCommercial 3.0 Unported License. (CC BY-NC 3.0). Modified from original.

    OpenStax College. (2013). Concepts of biology. Retrieved from OpenStax CNX. Available under Creative Commons Attribution License License 3.0 (CC BY 3.0). Modified from Original.

    Contributors and Attributions

    5.5: Resources is shared under a CC BY-NC license and was authored, remixed, and/or curated by LibreTexts.

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