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Interest Grabber
Section 15-1
A Trip Around the World
While on his voyage around the world aboard the H.M.S. Beagle, Charles Darwin
spent about one month observing life on the Galápagos Islands. There, he
encountered some unique animals, such as finches and tortoises.
1. On a sheet of paper, list five animals that you have encountered in
the past two days.
2. How do these animals differ from the finches and tortoises of the
Galápagos Islands? (Examine Figures 15–3 and 15–4 in your
3. Propose a hypothesis to account for the differences between the
animals that you observed and the finches and tortoises of the
Galápagos Islands.
Section Outline
Section 15-1
The Puzzle of Life’s Diversity
A. Voyage of the Beagle (1831)
B. Darwin’s Observations
1. Patterns of Diversity
2. Living Organisms and Fossils
3. The Galápagos Islands
C. The Journey Home
Words to Know
Evolution – change over time
Theory – well-supported testable explanation of natural
Fossils - preserved remains of ancient organisms
Hutton and Lyell – this geologic understanding
influenced Darwin; recognized that Earth is millions of
years old, and the processes that changed Earth in the
past are the same processes that operate in the present
Principles of Geology – Lyell’s book
Jean-Baptiste Lamarck
•French naturalist
•Selective use or disuse of organs (1809)
•Inheritance of acquired traits
•Theory is incorrect: he did not know that an organism’s
behavior has no effect on its inheritable characteristics
•Book-System of Invertebrate Animals
Thomas Malthus
Thomas Malthus (1798)
•Reasoned that if the human population continued to
grow unchecked, sooner or later there would be
insufficient living space and food for everyone
•Proposed that war, famine, and disease limited the
growth of human populations
Figure 15–1 Darwin’s Voyage
Section 15-1
Giant Tortoises of the Galápagos
Section 15-1
Pinta Island
Intermediate shell
Santa Cruz
Santa Fe
Hood Island
Isabela Island
Dome-shaped shell
Saddle-backed shell
Interest Grabber
Section 15-2
My, How You’ve Changed!
Prior to the 1800s, life scientists knew that living things changed over
generations. They just didn’t know how these changes were brought about.
1. Divide a sheet of paper into two columns and title the first one Inherited
Characteristics. Title the second column Acquired Characteristics. In
the first column, list the characteristics that you believe you have
always had. For example, you may have brown eyes or curly hair.
2. In the second column, list your acquired characteristics. For example,
you may have learned how to play a musical instrument.
3. Which of the items in your lists do you think you might pass on to your
children? Explain your answer.
Section Outline
Section 15-2
Ideas That Shaped Darwin’s Thinking
A. An Ancient, Changing Earth
1. Hutton’s Theory of Geological Change
2. Lyell’s Principles of Geology
B. Lamarck’s Theory of Evolution
1. Tendency Toward Perfection
2. Use and Disuse
3. Inheritance of Acquired Traits
4. Evaluating Lamarck’s Theory
C. Population Growth
Movement of Earth’s Crust
Section 15-2
rocks form in
horizontal layers.
When part of Earth’s
crust is compressed,
a bend in a rock
forms, tilting the rock
As the surface
erodes due to water,
wind, waves, or
glaciers, the older
rock surface is
New sediment is
then deposited
above the exposed
older rock surface.
Figure 15–7 Lamarck’s Theory of
Section 15-2
Interest Grabber
Section 15-3
When Is a Flipper a Wing?
All living things are related. Some relationships are easy to see—
your pet cat may not roar like a lion, but it clearly resembles one.
Other relationships are less obvious.
Interest Grabber continued
Section 15-3
1. On a sheet of paper, construct a table that has five columns and six
rows. In the columns, write the following heads: Animal Group,
Example, Legs, Fins, and Tail. Then, place the following animal groups
in their own row: Mammal, Bird, Fish, Amphibian, Reptile, and Insect.
2. Give one example for each group, and then fill in the information
for that example. For Legs, write in the number of legs that each
animal has. Do animals with fins have legs? Do animals with wings
have legs? If so, how many?
3. Can you tell from your table if a fish is more closely related to a bird
or to an amphibian? Explain your answer.
Section Outline
Section 15-3
15–3 Darwin Presents His Case
A. Publication of On the Origin of Species
B. Natural Variation and Artificial Selection
C. Evolution by Natural Selection
1. The Struggle for Existence
2. Survival of the Fittest
3. Descent With Modification
D. Evidence of Evolution
1. The Fossil Record
2. Geographic Distribution of Living Species
3. Homologous Body Structures
4. Similarities in Early Development
E. Summary of Darwin’s Theory
Words to know
Natural variation – differences among individuals of a
species (physical strength, resistance to disease, vision,
hearing, etc.)
Artificial selection – selection by humans for breeding of
useful traits from the natural variation among different
organisms (breed largest hogs, fastest horses)
Struggle for existence – members of each species
compete regularly to obtain food, living space, and other
necessities of life
Fitness – ability of an individual to survive and
reproduce in its specific environment (a result of
Adaptation – any inherited characteristic that increases
an organism’s chance of survival (sharp quills, behavior
in which some animals live and hunt in groups)
Survival of the fittest – individuals best suited to their
environment survive and reproduce most successfully
Natural selection – survival of the fittest; over time, it
results in changes in the inherited characteristics of a
population (These changes increase a species’ fitness
in its environment.)
Descent with Modification – each living species has
descended, with changes, from other species over time;
implies common descent (structures, niches, habitats)
Evidence of Evolution
1. Fossil record (fossils from sequential layers of rock)
2. Geographic distribution of living species – common
mainland ancestors
3. Homologous body structures – structures that have
different mature forms but develop from the same
embryonic tissue; the greater the similarities among
homologous structures, the more recently particular
species last shared a common ancestor
Vestigial structures – traces of homologous structures
that do not affect the organism’s ability to survive
4. Similarities in early development (Embryos)
In their early stages of development, embryos of
chickens, turtles, and rats look similar
Concept Map
Section 15-3
Evidence of
The fossil record
distribution of
living species
body structures
in early
which is composed of
which indicates
which implies
which implies
remains of
Similar genes
Similar genes
Figure 15–14 Geographic Distribution
of Living Species
Section 15-3
Beaver and
Coypu and
Figure 15–15 Homologous Body
Section 15-3
Typical primitive fish
Summary of Darwin’s Theory
•Struggle for existence
•Survival of the fittest
•Descent with modification
•Natural selection
•Common ancestry