Dna comparisons show that some populations of brown

DNA comparisons show
that some populations of
brown bears are more
closely related to polar
bears than they are to
other brown bears. What
do you think this means
for the classifi cation of
polar bears?
FIGURE 18–12
Classification of
Pandas
Biologists used to classify the
red panda and the giant panda together.
However, cladistic analysis using DNA
suggests that the giant panda shares a more
recent common ancestor with bears than with
either red pandas or raccoons.
X Y Z
Lesson 18.2
•
Self-Test
•
Lesson Assessment
Often, scientists use DNA evidence when anatomical traits
alone can’t provide clear answers. Giant pandas and red pandas,
for example, have given taxonomists a lot of trouble. These two
species share anatomical similarities with both bears and rac-
coons, and both of them have peculiar wrist bones that work like a
human thumb. DNA analysis revealed that the giant panda shares
a more recent common ancestor with bears than with raccoons.
DNA places red pandas, however, outside the bear clade. So pandas
have been reclassifi ed, placed with other bears in the clade Ursidae,
as shown in Figure 18–12. What happened to the red panda? It
is now placed in a different clade that also includes raccoons and
other organisms such as seals and weasels.
522 Chapter 18 • Lesson 2

Changing Ideas About Kingdoms
What are the six kingdoms of life as they are now identified?
During Linnaeus’s time, the only known differences among living
things were the fundamental characteristics that separated animals
from plants. Animals were organisms that moved from place to place
and used food for energy. Plants were green organisms that generally
did not move and got their energy from the sun.
As biologists learned more about the natural world, they realized
that Linnaeus’s two kingdoms—Animalia and Plantae—did not reflect
the full diversity of life. Classification systems have changed dramati-
cally since Linnaeus’s time, as shown in Figure 18–13. And hypotheses
about relationships among organisms are still changing today as new
data are gathered.
Building the Tree of Life
Key Questions
What are the six kingdoms
of life as they are now identified?
What does the tree of life
show?
Vocabulary
domain
•
Bacteria
•
Archaea
•
Eukarya
Taking Notes
Concept Map As you read, con-
struct a concept map describing
the characteristics of the three
domains.
Plantae
Animalia
Protista
Monera
Plantae
Plantae
Archaebacteria Eubacteria Protista Fungi Plantae Animalia
Animalia
Animalia
Fungi Protista
Names of Kingdoms
First Introduced
1700s
Late 1800s
1950s
1990s
Kingdoms of Life, 1700s–1990s
FIGURE 18–13
From Two to Six Kingdoms
This
diagram shows some of the ways in which organisms
have been classified into kingdoms since the 1700s.
523
Lesson 18.3
•
Lesson Overview
•
Lesson Notes
THINK ABOUT IT
The process of identifying and naming all known
organisms, living and extinct, is a huge first step toward the goal of
systematics. Yet naming organisms is only part of the work. The real
challenge is to group everything, from bacteria to dinosaurs to blue
whales, in a way that reflects their evolutionary relationships. Over
the years, new information and ways of studying organisms have
produced major changes in Linnaeus’s original scheme for organizing
living things.