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Ch. 15 Darwin’s Theory of Evolution
• You can acquire new pants, but
you can’t change your GENES!
Ch. 15 Outline
• 15-1: The Puzzle of Life’s Diversity
– The Voyage of the Beagle
– Darwin’s Observations
– The Journey Home
15–1 The Puzzle of Life's Diversity
• What scientific explanation can
account for the diversity of life?
• The answer is a collection of
scientific facts, observations, and
hypotheses known as the theory of
• Evolution is defined as change over
• Evolution describes the process by
which modern organisms have
descended from ancient organisms.
• A scientific theory is a wellsupported testable explanation of
phenomena that have occurred in
the natural world.
• What process is described by
the Theory of Evolution?
• How modern organisms have
descended from ancient
15-1 Voyage of the Beagle
• Charles Darwin
contributed more to our
understanding of
evolution than any other
• Charles Darwin was
born in England in 1809
– In 1831 Darwin joined
the crew of the H.M.S.
Beagle as the ship’s
Voyage of the Beagle
–The voyage of the Beagle lasted five
15-1 Voyage of the Beagle
• Darwin made numerous observations
and collected many plant, animal and
fossil specimens
• This led Darwin to propose a
hypothesis about the way life
changes over time.
– This hypothesis is now called the
theory of evolution.
15-1 Darwin’s Observations
• Patterns of diversity
– Many plants and
animals seemed well
suited to their
15-1 Darwin’s Observations
• Patterns of
– Organisms
survived and
reproduced in
many different
– Not all
• What three patterns of
diversity did Darwin observe in
• The organisms were well
suited to their environment,
survived and reproduced in
different ways, lived in a
variety of places
15-1 Darwin’s Observations
• Darwin collected
– Fossil: Are
remains of ancient
• Some fossils
Darwin collected
resembled living
15-1 Darwin’s Observations
• Some fossils did not resemble any living
• As Darwin studied
fossils, new
questions arose.
• Why had so many
of these species
• How were they
related to living
15-1 Darwin’s Observations
• Darwin’s thoughts were greatly
influenced by his collection and
observation of species on his visit to
the Galapagos Islands.
15-1 Darwin’s Observations
• The Galapagos Islands
– Are off the west coast of South America
– Each Island has a different climate and
different organisms
that the
birds had
beaks on
each island
15-1 Darwin’s Observations
– Darwin noticed that the tortoises
had different shaped shells on
each island
15-1 The Journey Home
• After returning to England, Darwin
wondered if animals living on
different islands had once been
members of the same species.
15-1 The Journey Home
• According to this hypothesis, these
separate species would have evolved
from an original South American
ancestor species after becoming isolated
from one another.
• This hypothesis challenged the
accepted views on the age of the
earth and the origin of different species.
• Darwin did not publish his thoughts until
twenty-three years after his voyage on the
• What did Darwin hypothesize
about the diversity of the species
on the Galapagos Islands?
– The different species evolved from a
common ancestor after they became
isolated from each other.
Ch. 15 Outline
• 15-2: Ideas that Shaped Darwin’s
– An Ancient, Changing Earth
– Lamarck’s Evolution Hypotheses
– Population Growth
15–2 Ideas That Shaped Darwin's
• About the same time Darwin was
questioning the origin of life, other
people were traveling around the
world and making important
• They also began to challenge
established views about the natural
15–2 Ideas That Shaped Darwin's
• Some people, however, found
Darwin's ideas too shocking to
• Most Europeans in Darwin's day
believed that the Earth and all its forms
of life had been created only a few
thousand years ago.
An Ancient, Changing Earth
• James Hutton and Charles Lyell
were two geologists whose ideas
influenced Darwin
• Hutton proposed that layers of rock
form very slowly and others are
pushed up from the sea floor to form
mountains. (This takes a long time)
Lyell’s Principles of Geology
• Lyell believed that
the same
processes that
changed the Earth
in the past still
operate in the
• Lyell’s and
Hutton’s work
influenced Darwin
in two ways:
• 1) If the Earth
can change over
volcanoes) maybe
life can change
over time!
• 2) Life can change over time only if the
earth is very old.
• Why did Darwin’s, Hutton’s and Lyell’s
view of the age of the earth was not
accepted by some scientists?
15–2 Ideas That Shaped Darwin's Thinking
• Jean-Baptiste Lamarck and Thomas
Malthus were two other scientists who
shaped Darwin’s thinking
• Lamarck proposed that new species
changed over time by gaining or
loosing certain traits in their
15–2 Ideas That Shaped Darwin's Thinking
• Lamarck had two ideas:
1. Organisms can alter their bodies by “use
and disuse”
• Use: Use a structure and it will change
• Disuse: Structures not used will disappear
2. Acquired characteristics can be
• If you increase your muscle mass your
children will inherit your big muscles
Use and Disuse
Lamarck’s Evolution Hypotheses
• Although Lamarck’s
ideas were incorrect,
he was one of the
first ones to realize
that organisms are
adapted to their
environments and
propose a theory of
• What are some acquired traits that
are found in people today?
15–2 Ideas That Shaped Darwin's Thinking
• Another influence of Darwin was
Thomas Malthus.
• Malthus published a book in which he
stated that babies were being born
faster than people were dying. If the
trend continued:
– food and living space will run out.
Population Growth
• Darwin thought this theory applied
more to plants and other animals
because humans usually only have one
offspring at a time.
• How did Lamarck’s and Malthus’
theories influence Darwin?
Ch. 15 Outline
• 15-3: Darwin Presents His Case
Publication of On the Origin of Species
Inherited Variation and Artificial Selection
Evolution by Natural Selection
Evidence of Evolution
Summary of Darwin’s Theory
15-3 Darwin Presents His Case
• When Darwin returned to England in 1836,
he continued to study the specimens he
collected from the Galapagos Islands.
• Darwin discovered that the birds, tortoises,
and plants that he collected looked like
similar species on the South American
• However, the island species were different
from each other and the mainland species.
Darwin Presents his Case
• Over 20 years later, Darwin published all his
findings in a book called, On the Origin of
• He didn’t publish it earlier because it went
against the common beliefs about organisms.
Darwin Presents his Case
• Not only did Darwin propose the theory of
evolution, he also proposed a mechanism
of how evolution happens:
• The mechanism for evolution is called
natural selection
Inherited Variation and Artificial Selection
• One of Darwin’s most important insights is that
there is a lot of diversity within all species
• In inherited variation, organisms pass on their
traits to their offspring. This randomly occurs in
Inherited Variation and Artificial Selection
• In artificial selection, humans select for
variations in nature that are useful.
– The breeding of domestic animals and
plant crops are examples.
Evolution by Natural Selection
• Next, Darwin compared natural
selection and artificial selection, and
proposed his mechanism of how
evolution occurs.
• Darwin realized that organisms
competed for resources. This is called
the struggle for existence.
Evolution by Natural Selection
• Darwin noted that organisms better
suited to their environment (ex. Run
faster, hide from predators) survived
to reproduce and pass on their
• This is called survival of the fittest.
Evolution by Natural Selection
• Fitness: The ability of an animal to
survive and reproduce
• Adaptation: an inherited
characteristic that increases an
organism’s chance of survival
Evolution by Natural Selection
• Successful adaptations, Darwin
enables organisms to survive and
– Types of adaptations
• Structures
• Physiological processes
• Behavior
Evolution of Natural Selection
• Survival of the fittest: individuals that are
better suited for their environment survive
and reproduce most successfully. This is
called Natural Selection
• Over time, natural selection results in
changes in the inherited characteristics
of a population. These changes increases a
species’ fitness in its environment.
Evolution of Natural Selection
• Darwin proposed that over long periods of
time, natural selection produces organisms
that have different structures. Species
today look different than their ancestors
• Descent with Modification: Each living
species has descended, with changes from
other species over time.
Evolution of Natural Selection
• Descent with modification implies that
all living species are related to each
• All species, living and extinct were
derived from a common ancestor
15-3 Evidence of Evolution
• Fossil Record
• Geographic Distribution of Living
• Homologous Body Structures
• Embryology
Fossil Cephalopods
Darwin argued that the fossil record
provided evidence that living things have
been evolving for millions of years.
Evidence of Evolution
• Geographic Distribution of Living Species
– Similar organisms found in different places on
– Ex: Darwin’s Finches
– Organisms under the same environmental
“pressures” in different locations had similar
Homologous Body Structures
• Structures that have different mature forms
but develop from the same embryonic
– Ex. Wings and arms
– Help Scientist determine common ancestors
– Not all homologous structures serve important
Homologous Structures
Ancient lobe-finned fish
Homologous Body Structures
• Vestigial Organs: Organs reduced in size
(Traces of homologous organs in other
– Have little or no function
• Organisms that have similar
developmental stages as embryos
are more closely related to each
Summary of Darwin’s Theory
1. Individual organisms differ, and some of this
variation is inheritable
Organisms produced more offspring that can
survive and there is competition for limited
3. Individuals best suited to environment survive
and reproduce. Others die or leave fewer
offspring. This process of natural selection causes
species to change over time.
4. Species alive today are descended with