Speciation and Extinction Macroevolutionary patterns are grand transformations in
anatomy, phylogeny, ecology, and behavior that usually take place in clades larger than a
If the rate of speciation in a clade is equal to or greater than the rate of extinction, the
clade will continue to exist. If the rate of extinction in a clade is greater than the rate
of speciation, the entire clade will eventually become extinct.
Background extinction is extinction caused by the slow process of natural selection.
Mass extinctions affect huge numbers of species over a relatively short time.
Rate of Evolution Evidence shows that evolution has occurred at different rates for
different organisms at different times.
The idea that evolution occurs slowly and gradually is called gradualism.
In punctuated equilibrium, long periods of little or no change are interrupted by short
periods of rapid change.
Adaptive Radiation and Convergent Evolution Adaptive radiation is the process in which a
single species evolves into diverse species that live in different ways. Convergent evolution
is the process in which unrelated species come to look alike because they have evolved
similar adaptations in response to similar environments.
Coevolution Coevolution is the process by which two species evolve in response to changes in
each other over time. For example, plants evolved poisons that protected them from insects.
In response, insects evolved ways of protecting themselves from the poisons.
Speciation and Extinction
For Questions 1–4, write True if the statement is true. If the statement is false, change
the underlined word or words to make the statement true.
1. Large-scale evolutionary changes that usually take place over long
periods of time are referred to as speciation.
2. Many species disappear rapidly during a background extinction.
3. The rate of speciation in a clade must be equal to or greater than
the rate of extinction in order for a clade to survive.
4. Immediately after a mass extinction, biodiversity is dramatically
5. What are possible causes of mass extinction?
6. What effects have mass extinctions had on the history of life?
Rate of Evolution
7. Horseshoe crabs have changed little in structure from the time they first showed up in
the fossil record. Which pattern of evolution do horseshoe crabs likely follow—
gradualism or punctuated equilibrium? Explain your answer.
8. Why does rapid evolution occur more often in small populations?
9. Use the Venn diagram below to compare punctuated equilibrium with gradualism.
Adaptive Radiation and Convergent Evolution
Write the letter of the correct answer on the line at the left.
10. The process in which a single species or a small group of species evolves into
diverse forms that live in different ways is called
C. adaptive radiation.
D. convergent evolution.
11. The process by which unrelated organisms come to resemble one another is
C. adaptive radiation.
D. convergent evolution.
12. What contributed to the adaptive radiation of mammals?
A. the evolution of plants
C. the decrease in ocean depth
B. the extinction of most dinosaurs
D. continental drift
13. Which of the following is an example of convergent evolution?
A. bird’s wing and fish’s fin
C. shark’s fin and dolphin’s limb
B. human’s arm and bird’s wing
D. human’s leg and dolphin’s limb
14. What is coevolution?
15. ‘I’iwi birds have long, curved beaks that enable them to get nectar from tubular lobelia
flowers. Explain how these two species might have coevolved. What might happen if the
lobelia die out?
19.3 Earth’s Early History: The Mysteries of Life’s Origins Earth’s early atmosphere
contained toxic gases. The atmosphere also contained little or no oxygen .
In the 1950s, Stanley Miller and Harold Urey set out to determine if organic molecules
could assemble under early Earth conditions. They filled a container with water and
gases that they thought represented the composition of Earth’s early atmosphere. They
passed electric sparks through the mixture to simulate lightning. Soon, organic
compounds formed. The experiment showed that molecules needed for life could have
arisen from simpler compounds.
Under some conditions, large organic molecules form tiny bubbles called proteinoid
microspheres. Structures similar to proteinoid microspheres might have become the
first living cells. RNA and DNA also could have evolved from simple organic molecules.
The first known life forms evolved about 3.5 billion years ago. They were single celled
and looked like modern bacteria. Eventually, photosynthetic bacteria became common.
During photosynthesis, the bacteria produced oxygen. The oxygen accumulated in the
atmosphere. The rise of oxygen drove some life forms to extinction. At the same time,
other life forms evolved that depended on oxygen.
Origin of Eukaryotic Cells The first eukaryotes, or organisms with nuclei, evolved from
prokaryotes that began to develop internal cell membranes. One explanation for how
eukaryotes evolved is the endosymbiotic theory. This theory proposes that smaller
prokaryotes began living inside larger cells and evolved a symbiotic relationship with the
Sexual Reproduction and Multicellularity Sexual reproduction evolved after eukaryotic
cells. Sexual reproduction increased genetic variation, so evolution could occur more
quickly. Several hundred million years after sexual reproduction evolved, multicellular life
The Mysteries of Life’s Origins
1. What are protenoid microspheres?
2. Why do scientists think that RNA may have evolved before DNA?
Use the diagram of the Miller-Urey experiment to answer Questions 3–5.
3. Label the diagram to show which part of Miller and Urey’s apparatus simulated lightning
storms on early Earth.
4. What was the purpose of Miller and Urey’s experiment?
5. Explain the results of the Miller-Urey experiment. What did these findings suggest?
Origin of Eukaryotic Cells
6. Explain the endosymbiotic theory.
7. Draw the step in the endosymbiotic theory that shows the origin of chloroplasts. Label
the structures in your drawing.
Sexual Reproduction and Multicellularity
8. How did sexual reproduction speed up the evolutionary process?
9. What is the most likely cause of the great amount of diversity currently seen in
multicellular life forms?
Apply the Big idea
10. Once DNA evolved, what could have caused it to become the primary means of
transmitting genetic information instead of RNA?
Chapter Vocabulary Review (ALL OF 19)
Crossword Puzzle Complete the puzzle by entering the term that matches the description.
1. time span shorter than an era
1. scientist who studies fossils
2. fossil used to compare the relative ages of
fossils and rock layers
3. describes a species that no longer
7. theory that eukaryotic cells arose from
communities of several prokaryotes
4. method used to place rock layers and
their fossils in a time sequence (2
9. measures evolutionary time: geologic time
10. span of geologic time that is subdivided
11. the time required for half of the
radioactive atoms in a sample to decay
12. a species dying out because of the slow but
steady process of natural selection:
5. the process by which a species or
group of species evolves into several
different forms that live in different
6. process by which two species evolve in
response to changes in each other over
8. disappearance of many species at the