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CHAPTER 5: THE PROCESS OF EVOLUTION ANS
I. Natural Selection
A. Charles Darwin was the first to compile persuasive evidence supporting evolution
1. Evolution is genetic change in a population over time
2. Darwin’s theory transformed the natural sciences and serves as the basis of all biological
research today
3. Darwin served as a naturalist on the British naval ship the H. M. S. Beagle
a. The Beagle sailed for five years from England to South America to make naval maps
b. Darwin observed nature, collected samples of new plants and animals, and wrote about
places and organisms few people had seen
4. Darwin’s most unique findings were the diversity and uniqueness of organisms on the
Galapagos Islands, 1000 km of the coast of South America.
a. After comparing animals and animal fossils from the different islands, he observed
that they were different from organisms on the South American mainland
b. Darwin reasoned that some of the species might have originated in South America but
evolved to be different
c. Darwin found enormous tortoises on all Galapagos Islands
d. Tortoises had dome-shaped shells and short necks where they ate low-growing plants
e. They had saddle-shaped shells and long necks where they ate high-growing cactus
f. Darwin concluded that the different tortoises descended from a common ancestral
population in South America, but each evolved to fit its unique environment
g. Darwin observed that finches, on different islands had distinct beak sizes and shapes
h. He concluded that the finches, like tortoises, had common South American ancestor,
but that they became different to suit the different island habitats
i. Selective breeding occurs when people breed plants and animals, such as vegetables or
cows, to produce desired traits
j. Selective breeding does not produce new species; all dogs can still have offspring with
their common ancestor the wolf
B. Darwin’s theory of natural selection states the organisms with traits that allow them to survive in
a particular environments pass on traits that could lead to new species
1. Genetic Variation is the creation of a diversity of traits through gamete formation
a. A harmful trait may cause an organism to die; a beneficial trait will be passed on to the
next generation
b. Genetic variation is necessary for evolution by natural selection to occur
2. Animals often produce more offspring than available resources can support
a. Thomas Malthus described this “struggle to survive” among the human population
b. Darwin applied Malthus’ idea to competition for survival among individuals in a species
c. Organisms best prepared for living in specific habitats will survive and reproduce, and
their offspring will be best able to survive and reproduce as well
3. New species can develop if organisms with common ancestors become isolated and natural
selection causes them to differentiate in response to different environments
a. Inherited traits that increase an organism’s chance of surviving and reproducing in a
particular environment are called adaptations
b. Darwin’s theory of evolution by natural selection includes four steps: overproduction,
variation/competition, inherited variation, and natural selection
c. Populations evolve as favorable traits in a particular environments spread through
generations
4. After 20 years, Darwin published The Origin of the Species by Natural Selection.
a. Darwin developed the idea that all organisms have “descended with modification” from
common ancestors
b. Darwin believed that evolution by natural selection explains the diversity of modern
organisms
II. Adaptations and Extinction
A. Organism evolve adaptations for specific environments through natural selection
1. Adaptations are the result of a long process by which traits are passed from one
generation to another
a. people may interpret the word adaptation, believing adaptations occur within a
generation and/or are intentional rather that naturally selected
b. Not all inherited traits are adaptations; negative traits may stay in a population is they
are linked to beneficial ones
c. Positive traits may help an organism to survive; negative traits may cause it to die off
B. Two types of adaptations are structural adaptations and behavioral adaptations
1. Structural adaptations are aspects of the physical body that help and organism survive and
reproduce
a. Camouflage, or blending in with one’s surroundings, is a type of structural adaptation
b. Lizards change colors to blend in with their surroundings; young animals sometimes
have camouflage coloration when they are more vulnerable to predators
c. Mimicry is when one species, a species looks or behaves like another
d. Some harmless organisms look like other dangerous or poisonous organisms to
discourage predators
e. In another type of mimicry, a species fools its prey by looking inviting or familiar
2. Behavioral adaptations, also called instincts, depend on the actions of an organism
a. Clapper rails build their nest so that they will rise and fall with the wetland tides
b. The male satin bower decorates its nest to attract a female mate
C. A species becomes extinct when all of the individuals of that species are wiped out
1. Several major events in history of the Earth have lead to extinctions
2. Major causes of extinction are habitat destruction, loss of genetic diversity, and
introduction of exotic species
a. Habitat for plants and animals shrink as humans develop and occupy more space
b. The fewer the individuals left of a species, the less genetic variation in the population
c. A species is threatened if there are so few individuals that lack of genetic diversity
could lead to species extinction
d. The introduction of exotic species has few predators, it can out-compete native
species and push them toward extinction
3. If rapid environmental change occurs when only small population of a species exist, lack of
genetic variation could lead to extinction relatively quickly