Chapter 15 Darwin’s
Theory of Evolution
15-1 The Puzzle of Life’s Diversity
15-1 Vocabulary
EvolutionChange in a kind of organism over time; process by
which modern organisms have descended from
ancient organisms.
TheoryWell-tested explanation that unifies a broad range of
observations.
FossilPreserved remain or evidence of an ancient
organism.
The Puzzle of Life’s Diversity
1. Voyage of the Beagle
a. In 1831, Darwin set sail around the world
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
textbook.)
3. Propose a hypothesis to account for the differences between the
animals that you observed and the finches and tortoises of the
Galápagos Islands.
The Puzzle of Life’s Diversity
b.
Darwin made observations and collected
evidence to propose a hypothesis about the
way life changes over time
i.
ii.
Evolution: change over time (modern
organisms have descended from ancient
organisms)
Theory: a well-supported testable explanation of
phenomena that have occurred in the natural
world
The Puzzle of Life’s Diversity
2. Darwin’s Observations
a. Patterns of Diversity
i.
Organisms survived and produced offspring
in a variety of ways depending on their
environment
The Puzzle of Life’s Diversity
b. The Galapagos Islands
i.
These islands are close but have very
different climates
1. Hood Island: sparse vegetation
2. Pinta Island: greater rainfall & various plants
& animals
3. Isabella Island: rich vegetation easily reached
ii. The land tortoises were characteristic
of their environment
1. Shell shape varied based upon need for
body movement
2. Neck length reflected amount and types
of food available
Pinta
Pinta Island
Tower
Marchena
Intermediate shell
Fernandina
James
Santa Cruz
Isabela
Santa Fe
Hood Island
Floreana
Hood
Saddle-backed shell
15-1 Review
What did Darwin’s travels reveal to him
about the number and variety of living
species?
Darwin’s travels showed him that the diversity
of living species was far greater than he had
previously known.
15-1 Review
How did tortoises and birds differ among
the islands of the Galapagos?
Each Galapagos island had its own type of
tortoises and birds that were clearly different
from the tortoises and birds on other islands.
15-1 Review
What is evolution? Why is evolution
referred to as a theory?
Evolution, or change over time, is the process
by which modern organisms have descended
from ancient ones. Evolution is referred to as a
theory because it is a well supported
explanation of phenomena that have occurred
in the natural world.
15-1 Review
What is a fossil?
A fossil is the preserved remains of an ancient
organism.