Evolution is an ongoing process.

• 8.1 We can see evolution occurring right before our eyes.

Darwin journeyed to a new idea.

• 8.2 Before Darwin, many people believed that all species had been created separately and were unchanging.
• 8.3 A job on a ’round-the-world survey ship allowed Darwin to indulge his love of nature and make observations that enabled him to develop a theory of evolution.
• 8.4 Observing geographic similarities and differences among fossils and living plants and animals, Darwin developed a theory of evolution.

Four mechanisms can give rise to evolution.

• 8.5 Evolution occurs when the allele frequencies in a population change.
• 8.6 Mutation—a direct change in the DNA of an individual—is the ultimate source of all genetic variation.
• 8.7 Genetic drift is a random change in allele frequencies in a population.
• 8.8 Migration into or out of a population may change allele frequencies.
• 8.9 When three simple conditions are satisfied, evolution by natural selection is occurring.
• 8.10 A trait does not decrease in frequency simply because it is recessive.

Through natural selection, populations of organisms can become adapted to their environments.

• 8.11 Traits causing some individuals to have more offspring than others become more prevalent in the population.
• 8.12 Organisms in a population can become better matched to their environment through natural selection.
• 8.13 Natural selection does not lead to perfect organisms.
• 8.14 Artificial selection is a special case of natural selection.
• 8.15 Natural selection can change the traits in a population in several ways.
• 8.16 This is how we do it: By picking taller plants, do humans unconsciously drive the evolution of smaller plants?
• 8.17 Natural selection can cause the evolution of complex traits and behaviors.

The evidence for evolution is overwhelming.

• 8.18 The fossil record documents the process of natural selection.
• 8.19 Geographic patterns of species distributions reflect species’ evolutionary histories.
• 8.20 Comparative anatomy and embryology reveal common evolutionary origins.
• 8.21 Molecular biology reveals that common genetic sequences link all life forms.
• 8.22 Laboratory and field experiments enable us to watch evolution in progress.