EVOLUTION
Chapter 13
Section 1: Charles Darwin and
his theories
Darwin’s Theory of Evolution

Evolution, or change over time, is the
process by which modern organisms have
descended from ancient organisms.

A scientific theory is a well-supported
testable explanation of phenomena that have
occurred in the natural world.
Voyage of the Beagle
Voyage of Beagle
Dates: February 12th, 1831
 Ship: H.M.S. Beagle
 Destination: Voyage around the world.
 Findings: evidence to propose a
revolutionary hypothesis about how life
changes over time as a result of an
organisms environmental conditions.

Science Before Darwin’s Voyage
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Most people believed each species was a divine
creation.
Scientists were trying to explain the origin of fossils.
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Some tried to explain it by altering traditional explanations.
Others (including Darwin’s grandfather) proposed
mechanisms to explain how living things change over time.
1809: French scientist Jean Baptiste Lamarck proposed
a hypothesis for how organisms change over
generations.

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He believed that over the lifetime of an individual, physical
features increased in size b/c of use or reduce in size b/c of
disuse.
He also believed these changes were then passed on to
offspring.
Science Before Darwin’s Voyage

This is now known to be incorrect, however
he did correctly point out that the changes
that occur in species are due to the physical
conditions of life- this refers to an
organisms environmental conditions.
Darwin’s Observations
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During Darwin’s voyage on the Beagle, he
found evidence that species were not
unchanging.
Darwin was reading a book that discussed how
changes in the Earth could occur over many
years.
While he was out, he started to notice evidence
of this.
 Fossils- he found fossils in South America
of extinct armadillos. These armadillos
closely resembled, but were not identical to
the armadillos still living in the area.
Fossils
The Galapagos Islands
Located 620 miles off the coast of
Ecuador.
 He noticed that many plants/animals
resembled those of the nearby coast of
South America.
 Darwin hypothesized that the most simple
reason for this was that these animals had
migrated to the islands and then changed
over time.
 Eventually Darwin called this “descent
with modification” – what we now refer
to as evolution.

Animals found in the Galapagos
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Land Tortoises
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Darwin Finches
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Blue-Footed Booby
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Marine Iguanas
Animals
The Journey Home
 When
Darwin was 27, he returned
home, but did not report his findings.
 He continued to study his data, until
his confidence grew that he was correct
in his conclusions.
 His hypothesis: Separate species may
have arose from an original ancestor
Population Growth


Thomas Malthus-19th century
English economist
If population grew (more
babies born than die)
 Insufficient living space
 Food runs out (populations
are able to increase faster
than food supply increases).
 He proposed that human
populations do not grow
unchecked because of death
caused by disease, war, and
famine that slows
population growth.
 Darwin applied
this theory to
animals.
Growth of Populations

Population: includes all of the individuals of a
species that live in a specific geographical area
AND can interbreed (breed with one another).
Evolution by Natural Selection
 Darwin realized that Mathus’ conclusions about
human population growth applied to all species.
 Every organism has the potential to produce
many offspring during its life time.
 But, not all of them will survive.
Natural Selection

After gathering all of his information, Darwin
made a conclusion: “individuals that have
physical or behavioral traits that better suit their
environment are more likely to survive and will
reproduce more successfully than those that do
not have such traits”. Darwin called this natural
selection.
 Over time, the number of individuals that carry
favorable characteristics that are ALSO
inherited will increase in a population.
Therefore, the population will change. This
changes = evolution.
Publication of Origin of Species
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1844 Darwin wrote down
his ideas about evolution
& natural selection, but
didn’t publish his data due
to the controversy that
other scientist were facing
concerning this topic- he
wasn’t confident enough.
Finally, he wrote the book
& it was published in Nov
1859.
Darwin’s theory of evolution by natural
selection is supported by 4 major points.
1) Inherited variation exist w/in the genes of every
population or species (the result of random mutation &
translation errors).
2) In a particular environment, some individuals of a
population or species are better suited to survive (as a
result of variation) and have more offspring (natural
selection).
3) Over time, the traits that make certain individuals of a
population able to survive and reproduce tend to spread
in that population.
4) There is overwhelming evidence from fossils & many
other sources that living species evolved from organisms
that are extinct.
Darwin’s Ideas Updated

Change within populations:
 Darwin’s main point was that in any population, the
individuals that are best suited to survive & do well in
their environment will produce the most offspring. So,
the traits of those individuals will become more common
in each new generation.
 Now, we know that genes are responsible for inherited
traits.
 Natural selection causes the frequency of certain alleles
in a population to increase or decrease over time.
 Mutations & the recombination of alleles that occurs
during sexual reproduction provide for endless sources
of new variation.
Species Formation
Because the environment differs from place
to place, populations of the same species
living in different locations tend to evolve
in different directions.
 Reproductive Isolation is the condition in
which two populations of the same species
do not breed with one another b/c of
geographic separation, a difference in
mating periods, or other barriers to
reproduction.

Reproduction Isolation
As two isolated populations
of the same species
become more different
over time, they may
eventually become
unable to breed with one
another. Usually, when
this happens, the two
populations are
subsequently considered
to have become two
different species.
The Tempo of Evolution
Evolution is understood to be a gradual
process that occurs continuously.
 This is called gradualism.
 Some scientists believe that evolution of
some species may actually occur in short
spurts, followed by long periods of no
change. This change is called punctuated
equilibrium.

Natural Selection

Over time, natural
selection results in
changes in inherited
characteristics of a
population. These
changes increase a
species fitness in its
environment
Evidence of Evolution
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The Fossil Record
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Geographic Distribution of Living Things
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Homologous Body Structures
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Similarities in Early Development
Evidence of Evolution
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The Fossil Record
Geographic
Distribution of
Living Things-similar
environments have
similar types of
organisms
Homologous Body
Structures
Similarities in Early
Development
Section 2: Evidence of Evolution

Fossils: offer the most direct evidence that
evolution takes place.
 A preserved/mineralized remain or imprint of
an organism that lived long ago.
 Provide an actual record of Earth’s past
life-forms.
 Change over time can be seen in the fossil
record.
• ie. Fossilized species found in older
rocks are different from those found in
newer rocks.
After observing the differences in fossils, Darwin
predicted that intermediate forms between groups of
organisms would eventually be found.
 Some have been found.
 Some have not.
 These intermediate forms are called transitional
fossils.
 Any fossil which gives us information about a
transition from one species to another.
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Examples of transitional fossils
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Darwin’s theory is almost universally
accepted by scientists as the best available
explanation for the biological diversity on
Earth:
 Based on supporting evidence, most
scientists agree on these 3 points:
 The Earth is about 4.5 million years old.
 Organisms have inhabited the Earth for
most of its history.
 All organisms living today share
common ancestry with earlier, simpler
life forms.
Problems with fossils
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Many species have lived in environments where fossils
do not form.
The environments most likely to cause fossil formation
are wet lowlands, slow-moving streams, lakes, shallow
seas, and areas near volcanoes that spew out volcanic
ash.
The chances that organisms living in certain areas will
die at just the right spot to be fossilized are low.
Even if this does happen, the chances are low that the
dead body will be buried in sediment before it decays
and/or is eaten by scavengers.
Rate of decay varies among organisms (hard skeleton vs
soft skeleton).
Studying fossils

Paleontologist: scientists who study fossils.
 They analyze the sediments around the fossils.
 They use radiometric dating of certain rocks and
minerals to arrange fossils in order from oldest to
youngest.
 This creates a visual pattern of evolution.
Anatomy & Development

Studying the anatomy of different types of
organisms often reveals basic similarities in body
structures even through the structures function may
differ between organisms.
 Vestigial structures
 Homologous structures
 Embryonic development
 Homologous
Structures-structures that
have different mature forms in different
organisms, but develop from the same
embryonic tissue.
 Vestigial
organs-organs that serve
no useful function in an organism
 i.e.appendix, miniature legs, arms
Similarities in Early Development
Biological Molecules
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In order for biology to match up with the changes in
fossils, then changes in a gene’s nucleotide sequence
should build up over time also.
Proteins
 One idea is that if evolution has taken place and a
species has descended from a recent common
ancestor, then they should have few amino acid
differences in their proteins.
 This has been supported in test with hemolglobinthe same hemoglobin protein in several species was
analyzed and found to have few amino acid
differences.
DNA Sequences
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This pattern is not true for all proteins.
Some change faster than others, so the
relationship may not be seen, if it did exist.
Section 3- Examples of Evolution
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Natural Selection at Work
 In Darwin’s writings, he offered
examples of how natural selection could
have shaped life on Earth.
 KEY POINT: The environment dictates
the direction and amount of change.
 If the environment changes in the
future, the set of characteristics that
most help an individual reproduce
successfully may also change.
Factors in Natural Selection

The process is driven by 4 important points
that are true for all real populations.
 All populations have genetic variation
 The environment presents challenges to
successful reproduction.
 Individuals tend to produce more
offspring than the environment can
support.
 Individuals that are better able to cope
with the challenges tend to leave more
offspring than those who aren’t.
An example
Evolution of antibiotic resistant diseases.
 The bacteria needs to survive to
reproduce.
 Eventually, a mutation will occur in its
genome that will allow even one bacteria
cell to fight off the antibiotics. As it
reproduces, more antibiotic resistant cells
are made and the antibiotic currently used
becomes ineffective.
 Darwin’s Finches: different beaks utilized
during food shortage.
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Formation of a new species
Species formation occurs in stages.
 Natural selection favors changes that
increase reproductive success.
 So, species are improved to “fit” into their
environment (ie. Fitness).
 Accumulation of differences between
groups- divergence.
 Divergence leads to the formation of new
species.
 Formation of new species- speciation.
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Forming subspecies
In environments differ enough, then
separate populations of the same species
can become so different that they become a
new species.
 Populations of the same species that differ
genetically b/c of adaptations to different
living conditions become subspecies.
 Once they are different enough, the
subspecies may become a completely
separate species.
 Due to reproductive barriers that form.
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Summary of Darwin’s Theory
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Individuals in nature differ from one
another

Organisms in nature produce more offspring
than can survive, and many of those who do
not survive do not reproduce.
Summary of Darwin’s Theory
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Because more organisms are produce than
can survive, each species must struggle for
resources
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Each organism is unique, each has
advantages and disadvantages in the
struggle for existence
Summary (cont.)
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Individuals best suited for the environment
survive and reproduce most successful
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Species change over time
Summary (cont.)
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Species alive today descended with modification
from species that lived in the past
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All organisms on earth are united into a single
family tree of life by common descent