1
(
Evolution
)
 Theories of evolution assume that modern life
forms
have evolved
1. Evidence of Evolution
 Attempts to describe the mechanisms by which
organisms change over time have formed the
basis of the evolutionary theory.
Evidence of
Evolution
includes
The fossil record
Geographic
distribution of
living species
which is composed of
which indicates
Common
ancestral
species
which implies
which implies
Similar genes
Theories of Evolution
 Attempt to explain the diversity of life forms
on earth
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 Species diversity is actually based on the
variety of
 Adaptations - any
Evidence of Evolution continued:
A. Comparative Cytology
 Organisms with very similar structures are
usually
B. Comparative Biochemistry
 Analysis of enzymes and other proteins
show that a great deal of similarity
C. Comparative Anatomy
 Similar organisms can be shown to have
limbs,
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 These structures are known as
D. Comparative Embryology
 Reproductive processes in many different
organisms
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E. Geologic Record
 Fossils are commonly discovered in
sedimentary rock layers.
Water carries small rock
particles to lakes and
seas.
Dead organisms are buried
by layers of sediment, which
forms new rock.
The preserved remains
may later be discovered
and studied.
 The oldest fossil of the simplest life forms are
generally found in the bottom layers.
 This is an example of relative dating.
Sea
level
Sea
level
Sedimentary
rocks form in
horizontal layers.
When part of Earth’s
crust is
compressed, a bend
in a rock forms,
tilting the rock
layers.
As the surface
erodes due to water,
wind, waves, or
glaciers, the older
rock surface is
exposed.
New sediment is
then deposited
above the exposed
older rock surface.
 Scientists can determine the age of fossils
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F. Vestigial Structures: structures that do not
seem to have any use (are also reduced in size)
but are
• Human examples: appendix, tailbone
(coccyx),
• Animal examples: whales and pythons have
vestigial hind leg bones embedded in body
wall
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2. Evolutionary Scientists:
A. John Lamarck - Proposed the idea of
evolution that included two main ideas:
1. Use and Disuse
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-The more a structure was needed,
-A structure that was not used
2. Transmission of Acquired Traits
-Traits developed as needed
-An organism could pass these “acquired
traits” to future generations
result
-The favorable “adaptations” would
-Lamarck’s theories were an important
-Later experiments conducted by August
Weismann and others failed to
support
Lamarck’s theories.
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C. Charles Darwin
-19th Century naturalist from England
-Devised a theory of evolution based
-His theory forms the basis of the
 Darwin’s Five Main Ideas:
1. Overproduction: species have a tendency
to produce
2. Competition: Within each species there is
a struggle for survival that may eliminate
many
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3. Variation: Darwin noticed variation within
a species even though he could not
explain it. He knew nothing of genes.
4. Survival of the Fittest: Animals better able
to resist disease, withstand environmental
conditions,
5. Reproduction: Adaptive advantages of
one generation may be passed on to the
next, perpetuating them in the species.
-This process is
-Lamarck and Darwin compared:
• Lamarck: Giraffes have long necks due to
years of stretching to reach leaves on tall
trees and the passing on of the long necks to
offspring.
• Darwin: Giraffes necks naturally vary in
length. Those giraffes that possess a long
neck were able to reach the leaves on the tall
trees and survive.
D. Modern Evolutionary Theory
-Based primarily on
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-In addition it incorporates the information
available from
Five Main Ideas:
1. Production of variation
The reproductive process, meiosis and
fertilization, provide the method by
which new combinations of
Mutation
-An important process in providing
2. Natural Selection
-Individuals that survive are “selected”
and are assumed to be those best adapted to
survive
-Survivors tend to pass on the genes
associated with their adaptive
advantages.
3. Speciation
-When enough unique adaptations have
been accumulated, in a species’
population,
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4. Reproductive Isolation
-If two populations of species are
geographically separated from each other
for a sufficiently long period, they may
change so greatly that even
Pinta
Pinta Island
Tower
Marchena
Intermediate shell
Fernandina
James
Santa Cruz
Isabela
Santa Fe
Hood Island
Floreana
Hood
Saddle-backed
shell
Isabela Island
Dome-shaped shell
or, another example… the “Founder Effect”
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Sample of
Original Population
Descendants
Founding Population A
Founding Population B
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5. Time Frame for Evolution
a. Gradualism – Assumes that
evolutionary change
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-Supported by fossil records
-Gradual change of
b. Punctuated Equilibrium – Assumes that
species experienced long geographic
periods
-This stability is “punctuated” by brief
periods
-Punctuated equilibrium is supported by
fossil evidence in which little change is
noted between most sedimentary layers
but
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3. Heterotroph Hypothesis – how life began
-Assumes that the first primitive life
-Heterotrophs… (they had to eat)
Conditions of the Early Earth
 Earth formed from clouds of cosmic dust
and gas
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to
 After condensing to a semi-solid form, the
earth required hundreds of millions of years
cool.
 During that period, the earth remained a
hot environment filled with simple inorganic
substances
-These substances were mixed together in
the primitive atmosphere and oceans to form a
 It is believed that these random chemical
reactions
led to the synthesis of
 The large molecules came together to form
aggregates which are assumed to have
Stanley Miller
-Set up a controlled environment that simulated
the hot, thin soup theory.
-He was able to
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Mixture of gases
simulating
atmospheres of
early Earth
Spark simulating
lightning storms
Condensation
chamber
Water
vapor
Cold
water
cools
chamber,
causing
droplets
to form
Liquid containing
amino acids and
other organic
compounds
 The natural by-products of living cells
 Organisms evolved to use the CO2 to make
 These Pioneer Autotrophs produced free O2
which
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Evolution of Life
Early Earth was hot; atmosphere contained poisonous gases.
Small sequences of RNA may have formed and replicated.
Later prokaryotes were photosynthetic and produced oxygen.
First eukaryotes may have been communities of prokaryotes.
Sexual reproduction increased genetic variability, hastening evolution.