19.2 Patterns and Processes of Evolution
Identify the processes that influence survival or extinction of a species or clade.
Contrast gradualism and punctuated equilibrium.
Name two important patterns in macroevolution.
Explain the evolutionary characteristics of coevolving organisms.
The chart below shows key terms from the lesson with their definitions. Complete the chart by
writing a strategy to help you remember the meaning of each term. One has been done for you.
How I’m Going to Remember
The process by which a species has
evolved over a relatively short time
into several forms that live in different
The process in which two species
evolve in response to changes in each
The process in which unrelated
organisms evolve into forms that
resemble one another
A pattern of evolution that is slow and
Large changes made by the process
of evolution over a long period of time,
usually in clades larger than a single
Term used to describe when many
species become extinct at the same
A pattern of evolution in which long
stable periods are interrupted by short
periods of great change
The prefix co-is used to describe
things that happen together.
Coevolution is two species
Concept Map A concept map can help you organize information and show how ideas are
As you read Lesson 2, complete the concept map below.
the changes made by evolution over long periods of
time and across a wide number of organisms
can occur when
Rate of Evolution
Evolution does not always occur at the same rate. It can happen slowly over a long period of time.
It can also happen quickly. Gradualism describes evolution that occurs slowly over time.
Punctuated equilibrium describes a pattern of long periods of stability interrupted by shorter
periods of rapid evolution.
Follow the directions.
1. Label the diagram below that shows gradualism.
2. Label the diagram below that shows punctuated equilibrium.
Answer the questions.
3. Look at the diagram you labeled gradualism. How do you know that this shows evolution
occurring over a long period of time?
4. Look at the diagram you labeled punctuated equilibrium. How do you know that this diagram
shows evolution occurring rapidly?
5. Give one reason a species could evolve quickly in a short time.
Adaptive Radiation and Convergent Evolution
Adaptive Radiation One macroevolutionary process is adaptive radiation. In adaptive
radiation, a single species or small group of species evolves over a short time into many forms
that live in different ways. Adaptive radiation often happens when there is a dramatic change in a
species’ environment. The evolutionary changes that occur allow the organism to survive. The
diagram below shows part of the adaptive radiation of mammals.
Look closely at the diagram. Pay close attention to the relationships among mammal groups.
Answer the questions.
1. Which group is most closely related to the sirenians?
2. Which group is most closely related to artiodactyls?
3. Which group(s) had a mammalian ancestor?
D. All of the above
4. Adaptive radiation is the process by which
A. species evolve together.
B. unrelated species evolve to look alike.
C. one species evolves into many forms that live in different ways.
D. one species evolves into a single new species.
5. Which two animals are believed to be more closely related?
sirenians and hyracoids
sirenians and tubulidentates