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• Darwin’s Theory
• Evidence of
Evolution
• The Fossil Record
Darwin’s Theory
• What important observations did
Darwin make on his voyage?
• What hypothesis did Darwin make to
explain the differences between
similar species?
• How does natural selection lead to
evolution?
Key Terms
Adaptation -
A trait that helps an
organism survive and
reproduce.
Evolution -
The gradual change in a
species over time.
Fossil -
The preserved remains or
traces of an organism
that lived in the past.
Key Terms
• Natural
Selection -
Individuals that are better adapted
to their environment are more
likely to survive.
• Scientific
Theory -
A well-tested concept that explains
a wide range of observations.
• Species -
A group of similar organisms that
can mate with each other and
produce offspring.
• Variation -
Any difference between individuals
of the same species.
Charles Darwin
• A “naturalist” –
studied the natural
world.
• Sailed on the Beagle
to the Galapagos
Islands.
• Observed many
unusual organisms on
the island.
– Giant tortoises
– Blue-footed booby
– Galapagos finches
The Voyage of the Beagle
• The Beagle made many stops along the
coast of South America stopping at the
Galapagos Islands.
• Darwin observed living things as he
traveled and tried to make connections
about the relationships among those
organisms.
– Diversity of living things
– Remains of ancient organisms
– Unique characteristics of organisms on the
Galapagos.
Darwin’s Observations
• The theory of
EVOLUTION by
NATURAL SELECTION
• Evolution
– The gradual change in a
species over time.
• Natural Selection
– Individuals that are
better adapted to their
environment will
survive and reproduce.
DIVERSITY
• The variety of life on
Earth.
• Darwin was amazed
by the tremendous
diversity of living
things that he saw.
• Scientists have
identified more than
1.7 million species of
organisms on Earth.
FOSSILS
• The preserved remains
or traces of an
organism that lived in
the past.
• Darwin was puzzled
by some of the fossils
he observed.
• He saw fossil bones of
animals that had died
long ago but yet
resembled the bones
of organisms alive in
Darwin’s time.
Galapagos Organisms
• Darwin observed many
unusual life forms on these
small islands.
• He compared Galapagos
organisms to organisms
that lived elsewhere.
• He also compared
organisms on different
islands in the Galapagos
group.
• He tried to make
connections using the
similarities and differences
he observed.
Comparisons to
South American Organisms
• The Galapagos organisms resembled many of those in
South America.
• Important differences between the organisms on the
islands and those on the mainland were important in
determining how the species ended up on the islands.
• Darwin hypothesized that a small number of different plant
and animal species had come to the Galapagos Islands from
the mainland.
– Blown out to sea during a storm
– Set adrift on a fallen log
• Once on the islands, the organisms reproduced and over
time, their offspring became different from their mainland
relatives because of their environment.
IGUANAS
• The iguanas on the
Galapagos Islands
had large claws.
– Grip slippery rocks
– Feed on seaweed
• The iguanas on the
mainland had
smaller claws.
– Climb trees
– Eat leaves
Comparisons
Among the Islands
• Darwin noticed many
differences among
organisms as he
traveled from one
island to the next.
• Darwin was able to
identify which island
an organism came
from just by looking at
it.
TORTOISES
• Some had domeshaped shells.
• Some had saddleshaped shells.
• Tortoises lived
inland and became
like “land-dwelling
mammals” grazing
on vegetation.
GALAPAGOS FINCHES
• Each species was
well ADAPTED
(suited) to the life
it led.
• Beak shape was
based on their diet.
– Narrow, needle-like
beaks = insects
– Strong, wide beaks
= seeds
Adaptive Radiation
• The evolutionary diversification of a single
lineage into a variety of species with different
adaptive properties.
Theory of Evolution
• Darwin spent 20 years consulting with other
scientists, gathering more information, and reevaluating his observations from his trip on the
Beagle before he developed his theory of evolution.
• Plants or animals faced with different conditions will
gradually change over many generations in order to
become better adapted to their conditions.
Selective Breeding
• The process of selecting a few organisms with
desired traits to serve as parents of the next
generation.
• By repeatedly allowing only organisms with the
desired traits to reproduce, the more desirable
trait becomes common and highly favorable in
the offspring.
• Darwin made connections between the practice
of selective breeding and organism behavior in
nature as evidence for his theory of evolution.
Natural Selection
• In 1858, Darwin
proposed an
explanation for
how evolution
could occur in
nature.
• Evolution occurs
by means of
NATURAL
SELECTION.
Natural selection is the process by which individuals
that are better adapted to their environment are
more likely to survive and reproduce than other
members of the same species.
Factors Affecting the
Process of Natural Selection
• Overproduction
• Variations
• Competition
• Selection
• Environmental
change
• Genes
OVERPRODUCTION
• Most species
produce far more
offspring than can
possibly survive.
• A large number of
offspring creates
competition for
resources.
VARIATIONS
• Members of a
species differ from
one another in
many of their
traits.
• Variations are
linked to
environmental
conditions.
COMPETITION
• Limited resources
creates competition
among members of a
species.
• Direct
– Physical fights
• Indirect
– Searching for food
– Avoiding predation
SELECTION
• Some variations make
individuals better
adapted to their
environment.
• Individuals who are
better adapted survive
and reproduce.
• Helpful variations may
gradually accumulate in
a species, while
unfavorable ones may
disappear.
ENVIRONMENTAL CHANGE
• A change in the
environment can affect an
organism’s ability to
survive.
• The environmental change
can gradually lead to
selection.
• The Galapagos Islands are
a prime example of how
the environment can lead
to the evolution of a
species by natural
selection.
GENES
• Without variations, all the
members of a species
would have the same
traits.
• Natural selection would
not occur because all the
individuals would have an
equal chance of surviving
and reproducing.
• Variations can result from
mutation and the shuffling
of alleles during meiosis.
• Genes are passed from
parents to offspring.
Natural Selection . . .
. . . Survival of the Fittest!