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Evolution Notes
Part 1: The History of Life
I. How Did Life Come to Be? - Theories
A. Dark Ages: “Life arose from non-living
matter.” This process is known as
spontaneous generation
Ex:
-rats from dirty clothes
-frogs from mud
-maggots from rotting meat
B. The Renaissance
1) 1668: An Italian doctor
named Francesco Redi
proposed the theory of
biogenesis “life comes from
life”
He designed an experiment
to test his theory
Redi’s Experiment
• Hypothesis = maggots come from eggs,
not rotting meat
• Control Treatment- No lid
• Result: maggots present
• Experimental Treatment #1 –
Lids
• Result: no maggots present
• Experimental Treatment #2 –
Screens
• Result: no maggots present
• Redi’s conclusion: biogenesis
(life comes from life) is correct!
• Addition: Life (baby maggots)
comes from life (eggs laid by
parents)
B. The Renaissance (continued)
2) 1745 – John Needham tried to prove that
spontaneous generation was correct
Steps to Experiment:
-boiled broth
-sealed broth
-bacteria grew
He felt this proved that bacteria (living) came from
broth (non-living) after killing all existing bacteria in
the broth…what was wrong with his experiment?
Answer: He didn’t boil the broth long enough, so he
didn’t kill off the existing (parent) bacteria in the broth
B. The Renaissance (continued)
3) 1770 – Lazzaro Spallanzani was an Italian
priest who believed Needham did not boil the
broth long enough to kill all existing bacteria
Steps to Experiment:
-Boiled broth longer
-Sealed broth
Results:
-Found NO BACTERIA
LONGER!
B. The Renaissance (continued)
4)1862 – Louis Pasteur did another
experiment with broth, which led to the
concept of pasteurization
Pasteur’s Experiment
• 2 different set-ups: Control
vs. Experimental
• Control Treatment: boiled
broth in an open neck
flask…a year later found
bacteria in flask
Open Neck
Flask
• Experimental Treatment:
boiled broth in a closed
neck flask (swan neck
keeps bacteria from
entering)… a year later
found NO bacteria
Addition: Pasteur’s
experiment supported
biogenesis, not
spontaneous generation
Swan Neck
Flask
II. Earth Before Life
A. Formation of the Earth
• 4.6 Billion Years Ago
• Early Atmosphere:
Volcanic Ash, CO2
(carbon dioxide), SO2
(sulfur dioxide), Methane,
Ammonia, lots of lightning!
B. Synthesis of Organic Molecules
• 1924 Alexander Oparin: Hypothesized
that conditions in early atmosphere
caused compound to form organic
(carbon-containing) molecules (ex: amino
acids)
B. Synthesis of Organic Molecules
• 1953 Stanley Miller and Harold Urey:
Set up an experiment to show that the following
reaction took place
Early earth
gases
Lightning
Amino Acids
( Proteins)
Miller and Urey’s Set-Up
C. Polymerization (putting together) small
organic molecules to make macromolecules
Building Blocks:
Macromolecules:
Monosaccharides  Sugars (Polysaccharides)
Fatty Acids
 Lipids (Fats)
Amino Acids
 Proteins
Nucleotides
 Nucleic Acids
Polymerization
D. First membrane and “protocells”
(early cells) called microspheres
• Membrane made out of phospholipids
E. Heredity and Replication
•
RNA was the first nucleic acid to
be used as genetic material
because it could “self-replicate”
(make a copy of itself)
•
Why would RNA need to be
able to self-replicate?
Answer: There were no
enzymes (ex: DNA polymerase)
able to assist with replication on
early Earth
•
It’s an RNA World!
III. Early Life
A. Unicellular Life
•
•
•
•
Simple cells
Prokaryotic = no nucleus
Bacteria
Heterotrophs =
“consumers”…can’t make
their own food!
B. Blue-Green Algae add
oxygen to atmosphere
• First organisms to be able to
photosynthesize
• What type of food do they
make? (Hint: It’s a sugar)
• What gas do they need to take
in to make oxygen?
C. Aerobic Respiration
• Organisms use glucose
to make ATP, an
energy- rich molecule
• What gas do they take
in, and what gas do
they release?
Remember the connections between
photosynthesis and cellular respiration!
D. Eukaryotic Cells
• Have a nucleus and membrane-bound
organelles (ex: golgi, ER, lysosomes) to do
specific jobs in the cell
• How did this happen? – Endosymbiosis…
when a large prokaryote “swallows” a small
prokaryote, which becomes its nucleus,
chloroplast, or mitochondrion
Endosymbiosis
• AKA Endosymbiont Theory
E. Multicellular Life
• Multicellular life
evolved towards the
end of the
Precambrian era in
Earth’s oceans
• Multicellullar
organisms can
specialize cells to do
different jobs
Part 2: Evolutionary Theories
• There are several scientists who observed
and predicted the causes behind
evolution
• Evolution = change in a population of
organisms over a period of time
• A population is a group of members of a
single species living in a particular area
A. Jean Baptiste Lamarck
• Theory of Use and Disuse: body parts that get used
become larger and stronger; Unused parts become
smaller
• Theory of Inheritance of Acquired Characteristics:
modifications acquired during the life of an
organism could be passed to offspring
Summary of Theories
1) Organisms constantly try to improve
2) This effort causes changes in body parts
3) Once a structure is modified, it is passed on to
future generations
The BEST traits/structures survive!
• Example for Lamarck’s Theory of Acquired
Characteristics: Giraffe Necks
• Hypothesis: giraffe necks are long because
ancestor giraffes had to stretch to reach their
food
B. Charles Darwin
• Geologist and biologist
• Sailed to South America and the
Galapagos Islands on the H.M.S.
Beagle
• Recorded observations of exotic
plants and animals for the Queen
• Studied finches and their beaks
• Concluded that beak shape is
related to food type
Darwin’s Finches
Darwin’s Theory of Natural Selection
1) There is variation in every population
2) Some variations are favorable
3) More young are produced in each generation
than can survive
4) There is competition for resources
5) Those that are successful go on to reproduce
6) Overtime, small changes accumulate in a
population because the best traits continue to
be passed on
Is this survival of the fittest?
• No! To be fit means more than just to
survive…you have to be able to reproduce
• Fitness = a single organism’s genetic
contribution to the next generation
• Over time, a population adapts as the
number of favorable traits increases
How do we get variation in a population?
• Mutations in the DNA create different gene forms
• Natural selection “chooses” individuals with
favorable mutations to reproduce
• Individuals can’t evolve…they are born with all
the genes they are ever going to have!
Populations can evolve as the % of good
mutations increases over time when individuals
with the best mutations survive and reproduce
better
Examples of Natural Selection
A. Peppered Moths: (Discuss with a
neighbor) – There are two forms of
peppered moth, light and dark. Before the
Industrial Revolution, light moths survived
and reproduced more effectively. After the
Industrial Revolution, dark moths survived
and reproduced more effectively.
WHY WAS THIS THE CASE?
2 Forms of Moth:
Light and Dark
Before
Industrialization
After
Industrialization
Peppered Moths - Answer
The light moths survived and reproduced better
before the IR because they camouflaged well on
trees with light bark (weren’t eaten by predators)
… so the light trait was more common
The dark moths survived and reproduced better
after the IR because they camouflaged well on
trees with dark bark (due to pollution)… so the
dark trait became more common
Examples of Natural Selection
B. Darwin’s Finches: Darwin noticed that
different species of finches on different
Galapagos Islands had differently shaped
beaks. There were also different types of
seeds found on each island.
WHY DO THE DIFFERENT SPECIES
HAVE DIFFERENT BEAK SHAPES?
Darwin’s Finches - Answer
Birds with beaks best adapted to a particular
food source on an island survived and
reproduced better, making this beak trait
more common in later generations
Part 3: Evidence for Evolution
A. Early Life Forms: Fossils
•
Fossil = a trace of a long-dead
organism, found in layers of sedimentary
rock; hard minerals replace tissues of
organism
Types of Fossils
• Mold = imprint in rock
• Cast = a mold filled with hard minerals
• Trace Fossils = signs of life
(footprints, burrowing, etc.)
• Resin Fossils = organisms
that have been preserved
nearly perfectly in plant
resin (amber)
• “Living Fossils” = any
living species that is nearly
identical to species
previously known only from
fossils
Can you identify the fossil type?
A
C
B
D
How do we determine the age of fossils?
• Relative Age – the approximate age based
on position in the layers of sedimentary
rocks
• Absolute Age – the exact age of a fossil
based on Radioactive Dating (carbon-14)
Relative Age: Rock Layers
• Which is older… a fossil found in layer 2 or
4?
Absolute Age: Radioactive Dating
• when “isotopes” of atoms in fossils decay
into other “isotopes”
• Remember: isotopes are the same atom
with different numbers of neutrons
• Measured in half-lives (how long it takes
for one-half of a sample of an isotope to
decay)
• Example: Carbon Dating (C-14C-12)
Absolute Aging Practice Problem
If the half life of C-14 is 15 years, meaning
half a sample of C-14 will decay into C-12 in
15 years…
• How much C14 (in a fraction) remains
after 45 years?
• How old is the sample if only 1/16 of the
carbon is in the C-14 form?
You need to add this to the back of your notes
packet!
B. Comparative
Anatomy
• Comparative Anatomy
– compare structures
found in modern
organisms with those
from ancient times
1) Homologous
Structures: inherited
from a common
ancestor, changed due
to different environments
Ex: Limb bones of whale,
bat, human, etc.
2) Analogous Structures:
similar in purpose, but
not inherited from a
common ancestor
Ex: Wings of insects vs.
bird
C. Vestigial Structures
• Features/structures that were useful to an
ancestor but are no longer useful
Ex: Whale pelvis,
Human tailbone +
appendix
D. Comparative
Embryology
• Finding similarities in
embryos ; organisms
sharing a recent ancestor
have more similar
embryos (discovered by
Ernst Haeckel)
E. Comparative Biochemistry
• Finding similarities in protein and DNA
sequences to look for relatedness
Below is a DNA sequence in several
different organisms…which organisms are
the most related?
Human
CCA TAG CAC CTA
Pig
CCA TGG AAA CGA
Chimpanzee
CCA TAA CAC CTA
Cricket
CCT AAA GGG ACG
Part 4: Types of Natural
Selection
A) Stabilizing Selection = individuals with the
average form of a trait have the highest fitness
B) Directional Selection = one extreme form of
trait is more successful
C) Disruptive Selection = BOTH extreme forms
are more successful than the average
D) Sexual Selection
• Females choose mates
based on certain traits
• Males with these traits
have higher fitness
(reproductive success)
http://www.youtube.com/
watch?v=gqsMTZQpmE&feature=fvwrel
Is there “unnatural selection?”
Artificial Selection = humans
“select” certain characteristics
in plants, dogs, etc., that they
find favorable
These organisms may not
necessarily survive and
reproduce better in nature
Part 5: The Creation of New
Species Through Evolution
• First off, how do we define a species?
• Morphological Species Concept – internal and
external structures are used to group organisms
into species
• Biological Species Concept– defines a
species as a population of organisms that can
successfully interbreed
• Speciation = formation of a
new species
• Reasons for Speciation
1) Geographic Isolation
2) Reproductive Isolation
-prezygotic (before
fertilization)
-postzygotic (after
fertilization)
There are two models of speciation, or how
populations change over time
Model #1: Gradualism (change happens
slowly, and new species are made at a
constant rate)
Model #2: Punctuated Equilibrium (there
are times of little or no change followed by
times of rapid change – often due to major
changes in the environment)
Stephen Jay Gould came up with this
model!
Gradualism
Punctuated Equilibrium
Another Way of Looking at It!
And yet another way of looking at it!
Part 6: Patterns of Evolution
A) Coevolution = change of two or more
species in response to one another
(Ex: predator/prey relationships)
Orchid Fly
Snails + Crabs
B) Convergent Evolution = organisms with
different ancestors become very similar
due to environment (Ex: sharks and
dolphins)
C) Divergent Evolution = two or more
related populations/species become
different (Ex: Darwin’s finches)
Divergent
Evolution
Convergent
Evolution
D) Adaptive
Radiation = an
extreme form of
divergent
evolution where
many related
species evolve
from a single
ancestor species