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Theory of Evolution
What is Evolution?
Evolution is a process of change through
time. A change in species over time.
Theories of evolution provide an
explanation for the differences and
similarities in structure, function, and
behavior among life forms.
Existing life forms have evolved from
earlier ones, by gradual changes in
Supporting Observations
1. Geologic Records – contains fossils that
indicate that simple organisms evolved into
increasingly complex multicellular organisms.
a.The earth is 4.5 – 5 billion years old
(determined by radioactive dating of rocks)
b.Fossils are direct or indirect remains of
organisms preserved in tar, amber, rock, etc.
c.Fossils have been found indicating that
organisms existed over 3 billion years ago.
Fossils
Fossil Evidence
The fossil sequence shows that the upper layers (strata)
contain fossils of younger organisms, whereas the lower
layers (strata) contain fossils of older organisms. The
fossils in the upper strata resemble some of the fossils in
the lower strata. This suggests links between older and
younger organisms.
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Supporting Observations
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2. Comparative Anatomy - Shows
similarities in anatomical features of
seemingly different organisms.

Includes Homologous Structures
Homologous Structures
•
Anatomical parts that are similar in
structure and origin, although they may
currently have different functions.
Analogous Structures
•
Anatomical Structures that look
different but have the same function.
Ex: whale and shark flipper
(whale skeleton is made of bone and shark
skeleton is cartilage)
Analogous Structures
Supporting Observations

3. Comparative
Embryology Comparison of
early embryonic
development
among groups of
organisms reveal
similarities which
suggest common
ancestry
Supporting Observations
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4. Comparative Biochemistry The closer the evolutionary
relationship between organisms,
the more alike the base sequences
are on the DNA molecule. As a
result, the more alike the amino
acid sequences are that make up
the proteins in the organisms.
Comparative Biochemistry
Baboon
Chimp
Lemur
Gorilla
Human
ASN
SER
ALA
SER
SER
THR
THR
THR
THR
THR
THR
ALA
SER
ALA
ALA
GLY
GLY
GLY
GLY
GLY
ASP
ASP
GLU
ASP
ASP
GLU
GLU
LYS
GLU
GLU
VAL
VAL
VAL
VAL
VAL
ASP
GLU
GLU
GLU
GLU
ASP
ASP
ASP
ASP
ASP
SER
THR
SER
THR
THR
PRO
PRO
PRO
PRO
PRO
GLY
GLY
GLY
GLY
GLY
GLY
GLY
SER
GLY
GLY
ASN
ALA
HIS
ALA
ALA
ASN
ASN
ASN
ASN
ASN
Differences between
Humans
Baboon
Chimp
5
0
Lemur
7
Gorilla
0
Theories of Evolution
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Attempts to explain the diversities
among species. Adaptations are a
major component of these theories.
Adaptation – any characteristic that
allows an organism to survive in its
environment.


Lamarck's Main Ideas
1. Use and Disuse - new
organs or structures arise
according to the needs of an
organism. The size is
determine by the degree to
which they are used.

2. Inheritance of Acquired
Characteristics – useful
characteristics acquired by an
organism during its lifetime
can be transmitted to its
offspring. These result in the
species being better suited to
their environment.
Lamarck's Giraffes
Was Lamarck correct?
•
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Tested by scientists who cut off
mouse tails. The tailless mice were
then bred. The result.....baby mice
WITH tails.
This challenged Lamarck's two main
ideas. The mice survived without tails,
but did not pass on the “tailless”
characteristic to their offspring.
Charles Darwin
•
•
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1809 – 1892
Naturalist who
traveled on the
HMS Beagle
documenting
organisms.
Developed the
Theory of
Natural
Selection
Theory of Natural Selection
•
•
Nature selects the organisms that
are better adapted to survive and
reproduce in a particular
environment.
There are 6 parts to the theory:
1.
2.
3.
4.
5.
6.
Overproduction
Competition
Variation
Survival of the Fittest
Transmission of favorable variations
Evolution of Species (Speciation)
Theory of Natural Selection
1.
Overproduction
More offspring
are produced
than can actually
survive.
Theory of Natural Selection
2.
Competition – Due to
overproduction, organisms
compete for resources
(materials needed to survive.
Ex: food, water, shelter)
Theory of Natural Selection
3.
Variation –
Individuals within
a species can vary
and have
different traits.
Theory of Natural Selection
Survival of the Fittest
During competition,
individuals with
favorable traits
(adaptations) will
survive. Those without
favorable traits will die.
Theory of Natural Selection
5.
Transmission of
Favorable Traits
Individuals with
favorable traits survive
and REPRODUCE,
passing on their traits to
another generation.
- High adaptive value
traits get passed on.
- Low adaptive value
traits die out.
Theory of Natural Selection
6.
Speciation - Over
many generations,
favorable adaptations
accumulate and many
changes lead to the
emergence of a new
species.
Modern Theory of Evolution
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Darwin's Theory of Natural Selection
is the presently accepted theory of
evolution.
However, Darwin's theory did not
explain sources of genetic variation
Variations within a species increase the
chance of survival when conditions
change.
Sources of Genetic Variation in a
Population
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1. Mutations – changes in base sequences in a
gene that may cause variation and new
characteristics.
Only mutations in gametes can become the
basis for evolutionary change.
2. Sexual Reproduction - Genes are randomly
combined, creating variation in offspring.
3. Isolation
Adaptive Value of Traits
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Adaptive Value – some variations give
individuals advantages over others in their
struggle for survival. They have a high
adaptive value.
In a changing OR unchanging environment:
–
traits with a high adaptive value
increase the chance of survival and
reproduction. They increase in
frequency.
–
Traits with low adaptive value will
decrease in frequency.
Sources of Genetic Variation in a
Population
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3. Isolation – Genetic variation may
increase if populations (groups of one type
of organism) are separated.
Geographic – Separated by a physical
barrier
Reproductive – Individuals reproduce at
different times (spring vs. fall)
Result of Isolation

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The gene pools of isolated populations may
become different as a result of isolation.
The populations may change so much that
they lose the ability to successfully
interbreed and are now considered
different species.
Ex: Galapagos Finches
Rate of Evolutionary Change
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Not all populations evolve at the same
rate.
Slow Evolution (Gradualism) – some
populations change very little over
millions of years, indicating that they
are well adapted (suited) to their
environment.
Ex: Horseshoe Crabs
Rate of Evolutionary Change
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Rapid Evolution (Punctuated Evolution)
- some populations of organisms change
a lot over millions of years, indicating
periods of stability with rapid periods
of change and evolution.
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Ex: Horses
Punctuated Evolution of Horses
Phylogenetic Tree
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Phylogenetic trees show evolutionary pathways,
and are used to show how closely related
organisms are.
They are used to show/reveal:
1.
All organisms come from a common
ancestor
2.
The relationship between different
species
3.
What species are extinct and still living
4.
Evolution involves a gradual change
Phylogenetic Tree
•
Which organism is most closely related
to the Hagfish? Why?
Phylogenetic Tree