The Theory Of Evolution

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Chapter 15
The Theory Of Evolution
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15.1
Natural Selection and the Evidence for Evolution
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I. Charles Darwin and Natural Selection
A. In 1831 a scientist named Charles Darwin set
sail on the H.M.S. Beagle.
1. The voyage lasted 5 years and covered S.
America the South Pacific.
1000 Km off the coast of South America OR 621
miles
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2. He collected and studied organisms during
his travels.
B. The organisms he collected in the Galapagos
islands were especially important.
C. Darwin came to some conclusions
1. Most organisms over-reproduce
2. Individuals struggle to survive
(competition for food, shelter, mates,
escaping predators).
D. Darwin identified an organisms ability to
survive as Natural Selection a mechanism
for change in a population of organisms.
1. Natural selection occurs when organisms
with certain variations survive,
reproduce, and pass their variations to the next
generation.
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II. Adaptations
A. Adaptation-a trait that makes a living thing
able to survive in its surroundings.
1. Adaptations develop over several
generations in a population.
2. One example of an adaptation is mimicry
where one organism resembles another
organisms that could be harmful.
On the next slide, Pick out which snake is
poisonous and which one is not poisonous.
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Harmless kingsnake
Harmful coral snake
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3. Some organisms blend into the environment -
camouflage
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Because well-camouflaged organisms are not easily
found by predators, they survive to reproduce.
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III. Evidence for Evolution
A. Fossils play an important role in
evolutionary evidence.
Camel Evolution
Oligocene 33 million years ago
Eocene 54 million years ago
Miocene 23 million years ago
Paleocene 65 million years ago
Present
Age
Organism
Skull and teeth
Limb bones
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B. Anatomy also plays an important role in
evolution.
1. Structural features with a common
evolutionary origin are called homologous
structures.
i. Homologous structures can be similar in
arrangement, in function, or in both.
Whale forelimb
Crocodile forelimb
Bird wing
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2. Another type of body feature that suggests
an evolutionary relationship is a
vestigial structurea body structure in a
present-day organism that no longer serves
its original purpose, but was probably
useful to an ancestor.
3. A structure becomes vestigial when the
species no longer needs the feature for its
original function, yet it is still inherited as
part of the body plan for the species.
i. Many organisms have vestigial structures.

• Vestigial structures, such as pelvic bones in the
  baleen whale, are evidence of evolution because
  they show structural change over time.

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The appendix is a vestigial structure in humans.
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Ostridge and Emu wings are vestigial structures.
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4. Body parts of organisms that do not have a
common evolutionary origin but are
similar in function are analogous
structures.
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C. Embryology is another way to determine if
two organisms are related.
1. An embryo is the earliest stage of growth
and development of both plants and
animals.
2. As an organism develops the embryos become
more distinguishable.
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D. Biochemistry also provides evidence about
relationships between organisms.
1. DNA comparisons offer the best evidence.
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Physiological adaptations can develop rapidly
Non-resistant bacterium
Antibiotic
Resistant bacterium
When the population is exposed to an antibiotic,
only the resistant bacteria survive.
The bacteria in a population vary in their
ability to resist antibiotics.
The resistant bacteria live and produce more
resistant bacteria.
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Physiological adaptations can develop rapidly
Non-resistant bacterium
Antibiotic
Resistant bacterium

• Today, penicillin no longer affects as many
  species of bacteria because some species have
  evolved physiological adaptations to prevent
  being killed by penicillin.