CHAPTER 13 Highlights 293
Key Concepts
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Key Terms
Section 1
population (278)
natural selection (279)
adaptation (279)
reproductive isolation (281)
gradualism (282)
punctuated equilibrium (282)Section 2
paleontologist (285)
vestigial structure (286)
homologous structure (286)Section 3
divergence (291)
speciation (291)
subspecies (291)The Theory of Evolution by Natural Selection
Charles Darwin concluded that animals on the coast of South
America that resembled those on the nearby islands evolved
differences after separating from a common ancestor.
Darwin was influenced by Thomas Malthus, who wrote that
populations tend to grow as much as the environment allows.
Darwin proposed that natural selection favors individuals
that are best able to survive and reproduce.
Under certain conditions, change within a species can lead
to new species.
Gradualism is a process of evolution in which speciation
occurs gradually, and punctuated equilibrium is a process
in which speciation occurs rapidly between periods of little
or no change.Evidence of Evolution
Evidence of orderly change can be seen when fossils are
arranged according to their age.
Differences in amino acid sequences and DNA sequences
are greater between species that are more distantly related
than between species that are more closely related.
The presence of homologous structures and vestigial struc-
tures in vertebrates suggests that all vertebrates share a
common ancestor.Examples of Evolution
Individuals that have traits that enable them to survive in a
given environment can reproduce and pass those traits to
their offspring.
Experiments show that evolution through natural selection
has occurred within populations of antibiotic-resistant
bacteria and in Darwin’s finches.
Speciation begins as a population adapts to its environment.
Reproductive isolation keeps newly forming species from
breeding with one another.