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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 characteristics through
generations.
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.

Supporting Observations

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

Vestigial Structures - Structures that serve no
apparent function.
Examples –
• Pelvis in a whale
• Appendix in a
human
• Coccyx (tail bone)
in a human
Supporting Observations

3. Comparative
Embryology Comparison of
early embryonic
development
among groups of
organisms reveal
similarities which
suggest common
ancestry
Supporting Observations

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
ASN
ALA
ASN
ASN
ASN
ASN
ASN
Differences between
Humans
Baboon
Chimp
5
0
Lemur
7
Gorilla
1
Theories of Evolution
•
•
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?
•
•
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
•
•
•
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



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

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
•
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.
Industrial Melanism: The case
of the peppered Moth
The peppered moth Simulation

http://www.techapps.net/interactives/pepperMot
hs.swf

Insect Resistance to insecticides

Antibiotic Resistance
Sources of Genetic Variation in a
Population
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


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
Adaptive Radiation
Rate of Evolutionary Change
•
•

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
Types of Natural Selection

Stabilizing Selection - Intermediate phenotypes selected
to survive.

Disruptive or Diversifying Selection – Extreme
phenotypes are selected.

Directional Selection 1 phenotype replaces another
due to environmental changes.

Other Types of Isolation
 Polyploidy
Rate of Evolutionary Change
•
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.


Ex: Horses
Gradualism vs. Punctuated
Equilibrium
Types of Evolution
Genetic Drift

Bottleneck Effect- The change is due to a natural
disaster where only a few organisms survive to
reestablish the gene pool.


Founder Effect- A small group of organisms
breaks away from a larger population to
colonize a new area.
Gene Flow – Migration of organisms between
populations.
Punctuated Evolution of Horses
Phylogenetic Tree
•
•
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
HARDY WEINBERG PRINCIPLE
The Hardy Weinberg Principle states that the allele
frequencies of alleles in a gene pool will remain
constant unless acted upon by other agents. Not
even segregation or recombination will change the
overall gene frequencies in a population.