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CHAPTER 15
Theory of
Evolution
CH 15.1 Charles Darwin
 Charles Robert Darwin
 Born February 12 1809 – April 19
1882)
 He was an English Naturalist.
 In 1830 Darwin took a trip around
the world on a ship called the HMS
Beagle where he made many
observations and went on to form
one of the most important theories
in biology.
The voyage of the Beagle
 In December 1831, the British ship HMS Beagle set sail from
England on a five year trip around the world.
 Darwin was
on board as a
Naturalist
 His job was
to learn as much
as possible about
the living things
he saw on the
voyage.
Darwin’s Observations
Darwin made many observations along his
stops on the Beagle
Darwin's observations included the diversity
of living things, the remains of ancient
organisms, and the characteristics of
organisms on the Galapagos Islands.
Darwin was amazed by the tremendous
diversity of living things. Scientists now have
identified more than 1.7 million species of
organisms.
The Galapagos Islands
 In 1835 the Beagle reached
the Galapagos Islands,
where Darwin observed
many unusual life forms on
these small islands such as
giant tortoises and giant
iguanas.
 When Darwin returned to
England, he compared
organisms to organisms that
lived elsewhere. He also
compared organisms on
different islands in the
Galapagos group.
 He was surprised by some of
the similarities and
differences he saw.
 Darwin found many
similarities between
Galapagos organisms
and those in South
America. However, there
were important
differences.
 Darwin was also
fascinated in particular
by the land tortoises in
the Galápagos.
 The Iguanas on the
Islands had large claws
that allowed them to grip
slippery rocks while the
iguanas on the mainland
had smaller claws to
climb trees.
 The shape of a tortoise's
shell could be used to
identify which island a
particular tortoise
inhabited.
 Giant tortoises varied in
predictable ways from
one island to another.
Adaptations
Like the tortoises, the finches on the
Galapagos Islands were noticeably different
from one island to the next.
The most obvious difference on the Finches
was their beak size and shape.
Darwin proposed that each species of finch
had a different size and shaped beak to suit
its environment. This is an example of an
Adaptation.
An Adaptation is a trait that helps an
organism survive and reproduce.
Evolution
 Darwin wanted to understand the different adaptations of organisms
on the Galapagos Islands.
 He hypothesized that the species gradually changed over many
generations and became better adapted to the new conditions.
 The gradual change in species over time is called EVOLUTION.
Evolution
 Evolution involves a change in a population over time
 Populations evolve
 Individuals do not evolve
Ideas of Darwin’s Time
• Catastrophism (Cuvier) the theory
that changes in the earth's crust during
geological history have resulted chiefly from
sudden violent and unusual events.
• Uniformitarianism (Lyell) the theory
that changes in the earth's crust during
geological history have resulted from the action
of continuous and uniform processes.
• Inheritance of acquired
characteristics (Lamarck)
Darwin’s Ideas
 Descent with modification
 Natural selection
Descent with modification
 Darwin used the phrase descent with modification to
describe the process of evolution.
 Descent with Modification-Each living organism has
descended, with changes from other species over
time
 Common Descent- were derived from common
ancestors
 Ex: Darwin's finches
Darwin’s Ideas
 Natural Selection
 Organisms in a population adapt to their environment as
the proportion of individuals with genes for favorable
traits increases.
 Adaptation – a trait that makes an individual successful to
survive in its environment.
 Those individuals that pass on more genes are
considered to have greater fitness
 Fitness – a measure of an individual’s hereditary contribution
to the next generation (how many offspring are produced!)
Natural Selection
In 1858, Darwin and Alfred Russell Wallace,
each proposed an explanation for how
evolution could occur in nature.
Darwin proposed that evolution could
happen by 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.
Natural Selection
Natural Selection
1.
Overproduction
2.
Genetic Variation
3.
Struggle to survive
4.
Differential reproduction (fitness)
Darwin identified factors that affect Natural Selection:
 1. Overproduction: Most species produce many more offspring that
can possible survive.
 2. Genetic Variations: any difference between individuals of the
same species.
 3. Struggle to survive: because resources are limited, members of a
species must compete with each other to survive.
 4. Selection: Darwin proposed that over a long time, natural selection
can lead to change. Helpful variations may gradually accumulate in
a species while the unfavorable ones disappear.
 Over time, natural selection results in changes in inherited
characteristics of a population. These changes increase a species
fitness in its environment
Lamarck’s Ideas on
Evolution
 French biologist jean Baptiste Lamarck (1774-1829) also
supported the idea that species change over time but
proposed a different way to explain HOW evolution
happens.
 Lamarck proposed that individuals could acquire traits
during their lifetime as a result of experience or
behavior, then could pass on those traits to offspring.
Lamarck called this idea: the inheritance of acquired
characteristics.
 This idea is no longer accepted by scientists
CH 15.2 Evidence of
Evolution
 The Fossil Record
 Geographic Distribution of Living Things
 Homologous Body Structures
 Similarities in Early Development
The Fossil Record
 The Age of Fossils
 Geologic evidence supports theories about
the age and development of Earth
 The Distribution of Fossils
 The fossil record shows that the types and
distribution of organisms on Earth have
changed over time.
 Transitional Species
 Fossils of transitional species show evidence
of descent with modification.
Evidence for Evolution:
 The Fossil RecordLayers show change
* Different organisms
lived at different times
* Species have differed
in a gradual sequence
of forms over time
(transitional species)
Evidence for evolution: Biogeography
 Geographic Distribution of Living Things-similar environments have
similar types of organisms
* The model of Descent with
modification provides an
explanation for these
patterns of distribution.
ANATOMY & EMBYOLOGY
 Homologous Structures-structures that have different mature
forms in different organisms, but develop from the same
embryonic tissue. (similar in structure and function AND have a
common ancestry in evolution)
 Analogous structures- closely related function but do not derive
from the same ancestral structure. (similar function but have a
different evolutionary origin)
Evidence for Evolution
Vestigial organsorgans that serve no
useful function in an
organism
i.e.) appendix,
miniature legs, arms,
whales pelvic bone.
Similarities in Early Development
Related
species show
similarities in
embryological
development
Biological Molecules
 Similarity in the subunit sequences of biological
molecules such as RNA, DNA, and proteins indicates a
common evolutionary history.
Hemoglobin Comparison
Developing the Theory of
Evolution
 Modern scientists integrate Darwin’s theory with other advances
in biological knowledge.
 Theories and hypotheses about evolution continue to be
proposed and investigated.
 Theories and hypotheses about evolution continue to be
proposed and investigated.

other advances in biological knowledge.
 Theories and hypotheses about evolution continue to be
proposed and investigated.
Evolutionary Relationships
Between Whales and Hoofed
Mammals
Phylogeny – the evolutionary
history of a species
CH 15.3 Evolution in Action :
Types of Evolution
 Convergent evolution - organisms that are not closely
related resemble each other because they have
responded to similar environments.
 Converge = to come together
 Divergent evolution - related populations become less
similar as they respond to different environments.
 Diverge = to come apart
Adaptive Radiation
•
Adaptive radiation is the divergent evolution of a single
group of organisms in a new environment.

Example – Galapagos finch beaks
Natural Selection of Anole Lizard Species
Artificial Selection
 The great variety of dog breeds is an example of
artificial selection.
Coevolution
 Coevolution – two species evolving in response
to one another
 Example – population of poisonous lizards evolves
a stronger poison over time. Populations of birds
that prey on lizards evolve a stronger tolerance to
poison.
 Example – antibiotic resistance
Convergent & divergent Evolution
 Convergent evolution is the process by which unrelated or distantly
related organisms evolve similar body forms, coloration, organs, and
adaptations.
Example: Convergent evol: WINGS of insects, birds and bats. (these are
also called analogous structures).
 Divergent evolution occurs when a group from a specific population
develops into a new species. In order to adapt to various
environmental conditions, the two groups develop into distinct species
due to differences in the demands driven by the environmental
circumstances. Adaptive radiation is a process in which one species
gives rise to multiple species that exploit different niches in the
environment. The ecological niches exert the selection pressures that
push the populations in various directions. On the various Galapagos
islands, finch species have become adapted for different diets: seeds,
insects, flowers, the blood of seabirds, and leaves.
Divergent evol: Wings of a bat, the humam forearm and fingers,the flipper
of a whale ,wing of a bird , foreleg of horse.
These are also known as homologous structures.