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, Mateo woke up soaked in sweat. He had a fever of 102.4 degrees 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
- Eighteenth-century Englishman Charles Darwin is one of the most famous scientists who ever lived. His place in the history of science is well deserved. Darwin's theory of evolution by natural selection represents a giant leap in human understanding. Darwin's theory contains two major ideas: (1) that evolution occurs. and (2) that evolution occurs by natural selection. Natural selection is the process in which living things with beneficial traits produce more offspring than others do.
- 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
- Milk naturally contains not only proteins and lipids; it also contains carbohydrates. Specifically, milk contains the sugar lactose. Lactose is a disaccharide (two-sugar) compound that consists of one molecule each of galactose and glucose, as shown in the structural formula below. Lactose makes up between 2 and 8 percent of milk by weight. The exact amount varies both within and between species.
- 9.8: Case Study Conclusion: Flu 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 Mateo, who you read about in the beginning of this chapter.
Thumbnail: A silhouette of human evolution. (CC BY SA 3.0 Unported; Tkgd2007).