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Biology LibreTexts

9: Biological Evolution

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  • This chapter outlines how Darwin developed his theory of evolution by natural selection, Wallace's contribution to the theory, and evidence for evolution. The chapter also describes tools for studying evolution, processes of microevolution and macroevolution, and how Earth formed and life first evolved.

    • 9.1: Case Study: Everyday Evolution
      One night in April 2009, Eric woke up soaked in sweat. He had a fever of 102.4 °F, chills, an intense headache, and body aches. He soon developed a sore throat and a bad cough.
    • 9.2: Darwin, Wallace, and the Theory of Evolution by Natural Selection
      The Grand Canyon, shown here, is an American icon and one of the wonders of the natural world. It is also a record of the past. Look at the rock layers in the picture.
    • 9.3: Evidence for Evolution
      Fossils are a window into the past. They provide clear evidence that evolution has occurred. Scientists who find and study fossils are called paleontologists. How do they use fossils to understand the past? The oldest horse fossils show what the earliest horses were like. They were only 0.4 m tall, or about the size of a fox, and they had four long toes. Other evidence shows they lived in wooded marshlands, where they probably ate soft leaves.
    • 9.4: Microevolution
      Individuals do not evolve because their genes do not change over time. Instead, evolution occurs at the level of the population. A population consists of organisms of the same species that live in the same area. In terms of evolution, the population is assumed to be a relatively closed group. This means that most mating takes place within the population. Evolutionary change that occurs over relatively short periods of time within populations is called microevolution.
    • 9.5: Macroevolution
      This garter snake preys on a variety of small animals, including small amphibians called rough-skinned newts. The newts produce a powerful toxin that is concentrated in their skin. Garter snakes have evolved resistance to this toxin through a series of lucky genetic mutations, allowing them to safely prey upon the newts. The predator-prey relationship between these animals has created an evolutionary "arms" race.
    • 9.6: Tools for Studying Evolution
      This interesting image is a 19th century representation of Earth that is based on an ancient Hindu myth. According to the myth, Earth rests on the backs of elephants, which in turn stand on the back of a giant turtle.
    • 9.7: Adaptation in Humans
      Do you remember this “got milk?” slogan from the 1990s? It was used in ads for milk in which celebrities were pictured wearing milk “mustaches.” While the purpose of the “got milk?” ads was to sell more milk, there is no denying that drinking milk can be good for one’s health. Milk is naturally high in protein and minerals. It can also be low in fat or even fat free if treated to remove the lipids that naturally occur in milk. However, before you reach for a tall, cold glass of milk, you might w
    • 9.8: Case Study Flu Conclusion and Chapter Summary
      In April 2009, the world was hit with a swine flu pandemic. The Centers for Disease Control estimates that within that first year, 43 to 89 million people worldwide contracted the swine flu, and that it contributed to 8,870 to 18,300 deaths. Some people with swine flu were spared serious complications, such as Eric, who you read about in the beginning of this chapter.

    Thumbnail: A silhouette of human evolution. Image used with permission (CC BY SA 3.0 Unported; Tkgd2007).