Download The Peppered Moth – A case of Natural Selection and Adaptation

Biology 3201
Notes
Evolution
Unit 4
Page 1 of 26
Evolution:
•
•
•
The relative change in the characteristics of a population over successive
generations.
A population is the smallest unit that can evolve
Any shift in a gene pool is also called evolution.
Question?
If evolution is the change in characteristics of a population over
successive generations, then how do these characteristics change?
Answer?
With the help of Adaptations and Variations.
Adaptation
•
A particular structure, physiology or behaviour that helps an organism survive and
reproduce in a particular environment.
o Ex: Camouflage, excellent sense of smell, hearing, vision etc.
Variation
•
A significant deviation from the normal biological form, function or structure.
o Ex: An albino moose, A partially sriped zebra etc.
The Peppered Moth – A case of Natural Selection and Adaptation
The peppered moth occurs in one of two variations.
•
•
Flecked (White wings with flecks of black)
Black ( Wing colour is black)
Until the mid 1900’s, the flecked moths lived and fed upon lichens on trees in England.
The flecked moths were camouflaged against the white background of lichens. The black
moths were easily seen and preyed upon. The flecked moths were able to survive and
pass on their genes to their offspring.
During the Industrial Revolution in England, black moths were able to gain an advantage
over the flecked moths. Black soot from factories killed the lichens and covered trees
providing an excellent source of camouflage for black moths. Now, the flecked moths
were easily seen and eaten. The black moths survived and passed their genes onto their
offspring.
The ratio of black moths to flecked moths was about to change again. In the 1950’s
England introduced “Clean Air Policy”. This allowed lichens to grow on trees again. As a
Biology 3201
Notes
Unit 4
Page 2 of 26
Evolution
result, the flecked moths were well camouflaged and the black moths were easily seen
and eaten. The ratio of black to flecked moths was changing again.
•
•
•
•
1959 Æ 9 /10 peppered moths were black
1985 Æ 5/10 peppered moths were black
1989 Æ 3/10 peppered moths were black
2010 Æ Black moth will be as rare as it was before the industrial revolution.
Summary - How do Peppered moths support evolution?
1)
2)
3)
In early 1850’s moths in England were mostly flecked (some were black).
Flecked ones survived because they were camouflaged
By the 1900’s air pollution made trees black. Black moths were able to survive.
1950’s saw pollution controls and now the flecked moth is surviving again.
Natural selection is the process whereby the characteristics of a population changes
because individuals with certain heritable traits survive local environments and pass
their traits to their offspring.
Peppered moths demonstrated Natural selection at work!!!!
A timeline of Evolution
Q.
How long has it taken for evolution to occur and from what did it start?
A.
Life is believed to have begun over 3500 million years ago with the earliest of
Cells.
3500 million
Single Cells
540 million
439 million
Marine Worms
Clams
Fish
245 million
Dinosaurs
66 million
Small mammals
1.6
Humans
Biology 3201
Notes
Evolution
Unit 4
Page 3 of 26
Natural and Artificial Selection – Mechanisms of Evolution
Natural Selection
•
Natural selection is the process whereby the characteristics of a population
changes because individuals with certain heritable traits survive local
environments and pass their traits to their offspring.
•
The environmental conditions determine which individuals in a population are
most fit to survive.
•
Genes from the surviving individuals are passed on to the offspring.
Fitness:
A measure of how well an organism fits with the environment.
An organism that is said to be “fit” is well suited to the current environment and
most likely will survive.
Artificial Selection
•
•
This is the human selection of particular traits by breeding.
Human activity determines which individuals in a population have the desired
traits to be passed on to the next generation.
Ex:
Breeding dogs, breeding horses to produce the fastest possible horse etc.
Note:
Not all breeding (artificial selection) brings about positive results.
Ex:
Pekinese and British Bulldogs are bred for flat faces, but this
causes respiratory problems.
Biology 3201
Notes
Evolution
Unit 4
Page 4 of 26
The Historical Contributors to Evolutionary Thought
Our ideas on evolution have been shaped by many people throughout the course of
history. We will examine some of the contributions to evolutionary thought and how this
helped create our current theories of evolution.
1.
Greek Philosophers
Greek philosophers such as Aristotle and Plato did not believe in evolution. They
said all organisms which could exist were already created.
2.
George Cuvier (1769 – 1832)
•
•
•
•
3.
James Lyell(1797 – 1875)
•
•
•
•
4.
Said to be the founder of Paleontology (Study of Fossils)
Opposed evolution
Studied the fossil record and noted that something was causing species to
appear and disappear.
Developed the idea of Catastrophism
o Catastrophism:
Idea that catastrophies account for the
disappearance and appearance of species within the fossil record.
Ex:
Noah’s flood caused disappearance of organisms from the fossil
record.
Expanded on Hutton’s idea of Gradualism.
o
Gradualism Æ Idea that earth’s geological features are in a
state of slow and continual change.
Lyell developed the theory of Uniformitarianism
o Uniformitarianism Æ Idea that geological processes operate at the
same rate today as they always did.
Lyell disbelieved in catastrophism.
Lyell said the earth was millions of years old instead of 6000 yrs old as
biblical people would say.
Thomas Malthus(1789)
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•
•
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An economist
Looked at populations. He studied animals and plants and noted that they
often outgrow their food supply.
Rapid growth such as this causes starvation and disease causing a
reduction in population.
Crowding and struggle for survival (competition for resources ) is what
keeps populations from exploding.
Biology 3201
Notes
•
5.
6.
Darwin borrowed Malthus’ ideas on “struggle for survival” and
realized that those organisms with the “best” traits for survival would
pass on their genes.
Jean Baptiste Lamarck (1744 – 1829)
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•
•
•
•
Published a theory of evolution in 1809 (year Charles Darwin was born)
Believed that organisms came from nonliving sources
Said that organisms respond to “needs” in their environment.
•
Modifications acquired during a lifetime can be passed on to offspring
This was known as his theory of Inheritance of acquired
characteristics:
o Ex:
A child would be strong because their dad was a
weightlifter.
o Ex:
A person who accidentally lost a finger would produce
offspring with nine fingers.
Proposed the idea that body parts used extensively to cope in the
environment would become stronger and stronger (Idea of “use and
disuse”)
o examples: biceps of blacksmith, giraffes neck
Wallace
•
•
•
7.
Evolution
Unit 4
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British naturalist
Did studies on a group of islands in Indonesia
Created the same theory as Darwin’s theory of Natural Selection.
Charles Darwin
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Wrote the book “The Origin of Species” in 1859 in which he published his
theory of evolution.
Did studies of Finche birds and tortoises on the Galapagos’ Islands
His theory of “Descent with Modification” had two main ideas.
1. Present life forms have arisen by descent and modification from an
ancestral species.
2. Natural selection is the mechanism of modification over long
periods of time.
Biology 3201
Notes
Evolution
Unit 4
Page 6 of 26
Darwin’s Theory of Natural Selection
Main Points
1.
2.
3.
4.
5.
NOTE:
Organisms produce more offspring that can survive.
Competition for limited resources causes a struggle to survive.
Individuals in a population can have variations that are heritable (can be
passed on to offspring).
Variations are often caused by MUTATIONS!
Only the organisms best suited to their local environment survive to
produce offspring. (idea that environment determines who survives)
Change is slow and gradual.
Darwin was unable to explain how the “best” traits were inherited by
offspring.
Why?
Darwin knew nothing about Mendel’s work and mutations which
provides genetic variation with a population.
Mendel’s work supported Darwin’s ideas.
The Modern Theory of Evolution or Modern Synthesis
This is the theory of evolution commonly accepted today.
•
This is a “meshing” of Mendel’s and Darwin’s ideas.
•
Darwin says that variations exist in a population allowing certain organisms to
adapt to their environment. These traits can then be passed on to offspring.
•
Mendel’s work points out that mutation is the cause of variation within a
population and it is the DNA that helps carry these “best” traits onto the next
generation.
Biology 3201
Notes
Evolution
Unit 4
Page 7 of 26
Evidence Supporting the Modern Theory of Evolution
The following are pieces of evidence that supports the modern theory of evolution.
1. Fossil Record
2. Biogeography
3. Comparative Anatomy
a. Homologous structures
b. Analagous structures
c. Vestigial structures
4. Comparative Embryology
5. Heredity
6. Molecular Biology
1.
Fossil Record
Fossil: Remains or traces of once living organisms. Often preserved in rock.
Fossil evidence supports evolution in the following ways:
a.
Fossils from more recent geological eras are more similar to present day
organisms than older fossils.
This supports the idea that life has evolved over time.
b.
Fossils appear in chronological order in sedimentary rock. Younger fossils
appear higher in sedimentary layers and are more complex than older
fossils appearing in deeper layers.
This supports the idea that has evolution has occurred, species of
organisms have become more complex!
c.
Transitional Fossils make links between different sets of related organisms
within differing fossil layers
Ex:
Archaeopteryx shows a relationship between reptiles and
birds.
This suggests that evolution is occurring over time from less
complex to more complex life forms.
Biology 3201
Notes
Unit 4
Page 8 of 26
Evolution
Finding the Age of Fossils / Dating Fossils
There are two methods to determine the age of a fossil.
A.
Relative Dating Æ
rock layer.
Ex:
Judging the age of a fossil according to its position in the
Fossil B is younger than fossil C but older than fossil A.
A
B
C
B.
Absolute Dating Æ Finding the exact age of a fossil using radioactive dating.
Radioactive dating Æ
A method of finding the age of a fossil using
the half-life of certain radioactive
substances that decay over time.
Note: The radioactive substance decays into a more stable daughter
element.
Half – Life: Period of time required for ½ of a radioactive isotope to
decay into a more stable element.
Representative radioactive isotopes with half-life
Radioactive Parent Stable Daughter
Half Life (years)
C14
N14
5730
U235
Pb207
713 000 000
K40
Ar40
1 250 000 000
Rb87
Sr87
48 800 000 000
Biology 3201
Notes
Unit 4
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Evolution
C14
C14 N14
N14
C14 C14
5730 years
One ½ life
5730 years
One ½ life
Notice that after each half-life, only ½ of the original C14 sample remains. The other ½
has been changed into N14 (the more stable form).
Percentage of original sample remaining
100%
Æ 50%
Æ
25%
2 half life’s
1 half life
1
Æ
½
Æ
Æ 12.5% Æ 6.25 % Æ 3.125% Æ 1.56 %
3 half life’s
¼
Æ
1/8
4 half life’s
Æ
1/16
Fractional amount of original sample remaining
5 half life’s
Æ
1/32
6 half life’s
Æ 1/64
Biology 3201
Notes
Evolution
Unit 4
Page 10 of 26
Calculations involving half-life
Here, we find either the age of the fossil, half-life or amount remaining.
A.
Finding amount of sample remaining.
Procedure:
Use ½n (Where n = # half life’s) to find multiplication factor. Then
multiply total by original mass.
Ex:
A 10 kg sample of C14 has underwent 4 half-lifes. How much of the
original sample remains?
Ans:
1/2n = ½4 = (½ ) (½) ( ½) (½) = 1/16.
Now, multiply 1/16 x original mass.
1/16 x 10 kg = 0.625 kg remaining.
B.
Finding the half-life (time required for a substance to decay to ½ its
original amount)
Ex:
A rock is found to be 33,000,000 years old and contains 1/64 of the
original sample. What is the half-life of the rock?
Answer:
First, find the number of half – life’s it took to reduce the sample
to 1/64.
To do this we ask the question, ½ to what power = 1/64? The
easiest way to find this is to ask the question, 2 to what power =
64. In this case 26 = (2) (2) (2) (2) (2) (2) = 64, so we conclude
that the number of half – life’s = 6.
Next, divide the age of the rock by the number of half-life’s and
you will find the value of 1 half – life.
In this case,
33000000 yrs
= 5500000 yrs / half − life
6half − lifes
Biology 3201
Notes
Evolution
Unit 4
Page 11 of 26
C.
Finding the age of the fossil
Ex:
A fossil contains 1/32 of the original U-235. What is the age of the fossil if
the half life of U-235 is 713,000,000?
Answer:
First, we need to find the number of half-life’s that reduces the
fossil to 1/32 of its original.
To do this we as the question, ½ to what power = 1/32. Again, the
easiest way to do this is ask, 2 to what power = 32.
In this case 25 = 32. This means there are 5 half-life’s that have
passed.
Next, we use the 5 half-life’s and multiply by the value of a single
half-life to get the fossil age. I this case we have the following:
5half − lifes x 713,000,000 yrs/half-life
= 3,565,000,000 yrs old
Biology 3201
Notes
Evolution
Unit 4
Page 12 of 26
Evidence Supporting Evolution continued ….
2.
Biogeography
•
•
3.
This is the study of the geographical distribution of species.
o Darwin noticed that the birds on the Galapagos’ islands were
similar to those on the mainland of South America.
Geographically close environments (desert and jungles of South America)
are more likely to be populated by related species rather than locations that
are geographically separate but environmentally similar ( desert of
Australia and a desert in Afreica).
Comparative Anatomy
•
This is a comparison of physical structures in differing organisms that may
suggest a common ancestor. Three methods are looked at:
o Homologous Structures:
These are body structures in different
species which have the same origin but differ in structure and
function.
Ex: Human arm, frog leg, bat wing, horse leg
These structures all have a similar number of
bones/ligaments suggesting they came from a common
ancestor, but they all have a different structure and
function.
o Analogous Structures:
These are structures that have
different origins, but similar function.
Ex: bird and insect wings.
o Vestigial Structures:
These are structures that were
functional in ancestors, but have no current function.
Ex:
Pelvic bones in baleen whales, wings in ostriches.
4.
Comparative Embryology
•
•
This is a comparison of embryos from various species to indicate
relationships among organisms.
Many embryos have similar stages of development.
Ex: All vertebrates go through a stage having a gill pouch.
Biology 3201
Notes
5.
Evolution
Unit 4
Page 13 of 26
Heredity
•
6.
Knowledge of heredity can explain how variations can occur in a
population allowing members of that population to be better suited to their
environment and thus undergo natural selection.
Molecular Biology
•
•
This is a comparison of the DNA and proteins within various species to
indicate relationships/similarity.
The closer the DNA sequences are between organisms, the more closely
related the species are. This may suggest a common ancestor.
Ex: Humans and chimpanzee DNA differs by only 2.5%
Population Genetics and Hardy Weinberg Principle
Population Genetics
•
This is a study of the genes in a population and how they may or may not change
over time.
Recall:
If there is a shift in the gene pool of a population then we know evolution
is happening.
Population
•
A localized group of a single species occupying a particular area.
Gene Pool:
• This is the total of all genes within a population.
•
•
Hardy-Weinberg Principle
A principle proposed by Hardy and Weinberg.
A model of a population that is not changing to help understand a population that
is changing.
Premise of the Principle
•
The principle states that in a population, under certain conditions, the frequency
of alleles will remain stable from generation to generation.
In other words, under certain conditions, a population’s genetic makeup will not
change meaning it is not evolving. It is in Genetic Equilibrium.
Biology 3201
Notes
•
Evolution
Unit 4
Page 14 of 26
The principle explains why recessive alleles do not disappear in a population over
time and it helps explain why dominant traits do not become more widespread.
Conditions necessary to establish a population Hardy-Weinberg Equilibrium
1. No mutations occur in the population
2. The population is large
3. Mating is random
4. There is no migration or emigration from the population.
5. No genotype has an advantage over another.
The Hardy-Weinberg Principle uses formulas to help calculate the frequency of alleles
and genotypes within a population.
1.
p+q=1
p = frequency of dominant allele
q = frequency of recessive allele
(How often the dominant allele shows up in
the total population)
(How often the recessive allele shows up in
the total population)
1 = 100%
Since there are only ever two alleles for a trait, the total amount of the alleles
always has to add up to 100% or 1.
2.
p2 + 2pq + q2 = 1
p2 = frequency of HOMOZYGOUS DOMINANT genotype
2pq = frequency of HETEROZYGOUS genotype.
q2 = frequency of HOMOZYGOUS RECESSIVE genotype.
Biology 3201
Notes
Unit 4
Page 15 of 26
Evolution
Let’s do an example to see how this all works!!!!
Suppose we have a population of Gerbils with the following conditions.
Phenotype
Black
Black
White
Genotype
BB
Bb
Bb
Number of Gerbils
196
168
36
Total # Gerbils
(192+168+36)= 400
Genotype
Frequency (BB, Bb,
bb)
Allele frequency (B
and b)
400
400
400
BB = 196/400 =
0.49
Bb=168/400=0.42
bb = 36/400 = 0.09
B = 196 + 168/800 = 0.7
b = 168+36/800=0.3
The table above shows the allele frequencies and genotype frequencies. Notice how they
are calculated:
Now, let’s use the formulas to arrive at the same information as above.
We know the following:
BB frequency = 0.49 = p2
Bb frequency = 0.42 = 2pq
Bb frequency = 0.09 = q2
According to Hardy-Weinberg, this means the following:
So, if we wanted to find the allele frequencies (B and b) we would find the square root
of p2 and q2.
p 2 = 0.49 = 0.7
p = 0.7
This means that 0.7 or 70% of all the alleles
in the population will be B.
q 2 = 0.09 = 0.3
q = 0.3
This means that 0.3 or 30% of the alleles
in the population will be b.
Biology 3201
Notes
Evolution
Unit 4
Page 16 of 26
According to Hardy-Weinberg, the relative proportions of these alleles will remain
unchanged if the population is in equilibrium or NOT evolving.
Let’s try another!
Q.
16% of a population expresses a recessive trait. What percentage of the
population will display the heterozygous trait?
A.
To find the recessive trait we have to find 2pq of the Hardy-Weinberg equation.
Remember, recessive trait = q2
The recessive trait is 16%. We convert this to a decimal to get 0.16
q = q 2 = 0.16 = 0.4
Since
p + q =1
p = 1− q
p = 1 − 0.4
p = 0.6
The percentage of individuals having the heterozygous trait is 2pq therefore;
2 pq = 2(0.4)(0.6)
2 pq = 0.48
= 48%
48% of the population will be Heterozygous.
Biology 3201
Notes
Evolution
Unit 4
Page 17 of 26
Mechanisms of Evolution
The following are mechanisms that cause genetic variation in a population and thus move
them away from Hardy – Weinberg equilibrium.
In other words, the following mechanisms cause populations to evolve!!!!
1.
Mutations
•
•
•
•
2.
These are changes in the DNA that can bring new alleles in a population.
The new alleles provide variations that cause evolution.
Mutations can be harmful, neutral or beneficial.
Mutations are beneficial if they provide a selective advantage which allows
certain organisms to adapt to their environment.
Ex: California Ground squirrel having the ability to break down rattlesnake
poison.
Genetic Drift
•
•
This is a change in allele frequencies in small populations caused by chance
alone.
o For example, in a small population mutations can cause allele frequencies
to change whereas in a large population the mutations may have little to
no effect on the frequencies. The gene pool will not shift if the
population is large.
o
The allele frequencies in small populations can change over time and this can lead
to evolution. Remember: In a non-evolving population (Hardy-Weinberg
equilibrium) the allele frequencies remain unchanged.
Causes of Genetic Drift
a. Bottleneck effect:
A situation in which, as a result of chance, some
alleles are overrepresented and others underrepresented because a
population has been reduced through natural disasters etc.
Ex: Elephant seals have passed through a bottleneck.
They have been overhunted causing their numbers to be reduced to about
20. Because of this, certain alleles have been eliminated (variety reduced).
The population has since grown to 30,000 having little variation. This has
resulted in a change in the allele frequency.
Biology 3201
Notes
Evolution
Unit 4
Page 18 of 26
b. Founder effect:
When a small amount of organisms (called a
founder population) move into a new area, chances are they do not contain
the entire genes representative in the parent population. This results in a
change in the allele frequencies.
Ex:
3.
Gene Flow
•
•
•
4.
Hawaiian Honeycreeper birds migrated from North America.
This is the movement of genes into or out of a gene pool.
This causes a change in the gene pool resulting in evolution.
If gene flow happens enough between two neighbouring populations they
may eventually merge into one population with a common genetic
structure.
Non – Random Mating
•
•
•
If a population mates on a random basis, genetic equilibrium is maintained
and the population does not evolve.
Normal populations do not undergo random mating. For example.
Individuals will mate more with their neighbours rather than distant
organisms.
There are two types of Non-Random Mating
o Inbreeding Æ Mating between closely related organisms.
ƒ This will cause a loss in variety in the population and the
allele frequencies will change.
o Assortive Mating Æ This is where organisms choose mates that
are similar to themselves.
ƒ Artificial selection (breeding of certain dogs) is an example
of assertive mating. The dogs being mated are choosing (or
are chosen for them) mates that are similar to themselves.
ƒ This causes a reduction in variety in the population causing
allele frequencies to change.
Biology 3201
Notes
5.
Evolution
Unit 4
Page 19 of 26
Natural Selection
•
A population’s characteristics can change because certain individuals
within the population have heritable traits that allow them to adapt to and
survive local environmental conditions.
• There are Three types of natural selection:
1. Stabilizing Selection:
o This is natural selection where an intermediate or normal
phenotype is favoured over the extremes.
ƒ Ex: birth weight (most babies born today are of average or
normal weight because the extreme (low or high) birth
weight babies are selected against (we do not see many low
birth weight or high birth weight babies anymore). The
“middle” or intermediate phenotype is favoured.
2. Directional Selection:
o Selection where one extreme phenotype is favoured over the
other. This causes a shift in the phenotypes in that direction.
o This type of selection is common during environmental change or
when a population migrates to a new habitat.
ƒ Ex: The modern horse (adapted to a grassland habitat) has
adapted from an ancestral horse (adapted to a forest
habitat). Most horses today, resemble the modern horse and
not the forest horse.
3. Disruptive Selection:
o Selection where both extremes of the phenotype are selected
rather than the middle (intermediate phenotype)
o The intermediate phenotype may be eliminated from the
population.
ƒ Ex: Coho Salmon. Males are either small (“Jack salmon)
or very large. No real medium size male salmon found in
the population.
6.
Sexual Selection
•
This is selection on the basis of being able to find a “suitable” mate in
which to produce offspring. Having the ability to choose a mate helps
ensure genetic information is passed on as well as introduces variety into
the population.
• Finding a suitable mate is based on two main characteristics:
a. Male competition Æ male competition can determine who gets the chance
to mate with a female.
b. Female choice Æ females choose who they mate with.
Biology 3201
Notes
Evolution
Unit 4
Page 20 of 26
Speciation
Speciation:
•
This is the formation of a species.
Biological Species:
Ex:
A group of organisms able to interbreed and produce fertile
offspring.
Horses and Donkeys are separate species. They are able to interbreed, but
the offspring produced are not fertile.
How do species form?
There are generally two pathways in which species are formed.
1.
Transformation Æ The formation of a species because of a series of
accumulated changes over time. One species changes into
another in this way.
Species
2.
Divergence Æ
changes
new species
The formation of species from a parent species/anscestor.
Species
Parent Species
Species
SPECIATION OCCURS WHEN TWO GROUPS IN A POPULATION BECOME
ISOLATED FROM EACH OTHER!!!!
These are caused by Barriers!!!
Types of Barriers that cause Speciation
a.
Geographical Barriers Æ When a population becomes divided by a
geographic boundary such as a canyon, river etc. This prevents interbreeding.
Over time natural selection causes genetic differences to become so large two
species form.
Biology 3201
Notes
Ex:
b.
Evolution
Unit 4
Page 21 of 26
Giraffes that become separated by mountains will eventually develop into
separate species.
Biological BarriersÆ
• These are barriers that keep species reproductively isolated.
• These barriers may be Pre-zygotic Barriers or Post-zygotic Barriers.
Pre-Zygotic Barriers
•
These are known as pre-fertilization barriers that either impede mating or
prevent fertilization.
i. Behavioural Isolation Æ bird songs, courtship rituals, pheromones etc. are
all species specific and prevent fertilization.
ii. Temporal Isolation Æ These are usually timing barriers. Several species
mate at different times during the year and as such are not able to mate.
iii. Habitat IsolationÆ Some species live in the same area but have different
habitats.
o Ex: North American Garter snakes. One species prefers open areas
while the other prefers water.
iv. Mechanical IsolationÆ Some species are anatomically incompatible thus
not allowing them to exchange sperm and egg.
o Ex: the genitals on certain species of insect work only on a lockkey system. If the lock does not fit the key, no fertilization can
happen.
v. Gametic Isolation Æ Sometimes the gametes from species do not even
meet. This prevents fertilization.
o Ex: sea urchins release their eggs into the water, but chemicals on
the surface of the eggs prevent sperm from a different species from
fertilizing them.
Biology 3201
Notes
Unit 4
Page 22 of 26
Evolution
Post –Zygotic Barriers
•
These are barriers that prevent a zygote from developing into a fertile
organism.
i.
Hybrid Invariability Æ Incompatibility of the two species may cause the
zygote to stop embryonic development.
ƒ Ex: Embryos of sheep/goats do not survive.
ii.
Hybrid Sterility Æ This is the production of an organism, but it is sterile.
ƒ Ex: Horse + donkey = Mule (sterile)
iii.
Hybrid Breakdown Æ Sometimes the first generation of offspring are viable
and can reproduce, but when their offspring reproduce their
offspring are sterile or weak.
ƒ Ex: Cotton plants produce generations of seeds that die!
Adaptive Radiation, Convergent/Divergent and Coevolution
1. Adaptive Radiation
• The diversifying of an ancestral species into a variety of species.
• This usually occurs after a novel characteristic has evolved or if there is a
mass extinction.
Ancestral Species
Species 1
Species 2
Species 3
Adaptive Radiation
Ex: Galapagos’ finches evolved from one common ancestor on islands.
2. Divergent Evolution
• This is where species that were once similar to an ancestral species
diverge to become different species.
Note: Adaptive Radiation is an example of Divergent Evolution
Biology 3201
Notes
Evolution
Unit 4
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3.
Convergent Evolution
• This is evolution where two completely unrelated species have similar
traits.
Ex: Birds and bees have wings (similar trait)
• Each species develops the same traits because they adapt to the same type
of environmental conditions.
• The species DO NOT come from a common ancestor.
4.
Coevolution
• This is evolution where two species change together where each species
responds to the changes in the other.
Ex:
Milkweed plants and monarch butterflies. The milkweed plant has
toxins in their leaves. Monarch butterflies eat the leaves and absorb
the toxins making them toxic. Most birds avoid monarch butterflies
for this purpose.
The Pace of Evolution
Q.
How fast does evolution occur?
A.
There are two theories/models that explain how fast evolution occurs. Both
examine the Fossil record.
1.
Gradualism
•
A model that says change occurs slowly and steadily before and after a
divergence.
•
Fossils show a slow and repeated change through the fossil record.
Biology 3201
Notes
2.
Evolution
Unit 4
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Punctuated Equilibrium
•
•
•
•
•
A model proposed by Gould and Eldridge.
A model that proposes evolution happens in “spurts”.
The model says that species undergo long periods of “stasis” where they
remain unchanged, followed by short periods of very rapid change
(spurts).
The changes are usually brought about by sudden environmental changes
such as volcanoes, earthquakes etc.
Species previously disadvantaged could now be advantaged and new
species could develop quickly.
The Origins of Life
Many theories exist that try to explain the origin and development of life on earth.
The following theories will be considered:
Chemical Evolution
Panspermia
Gaia Hypothesis
Heterotroph Hypothesis
Sybiogenesis (Symbiotic Theory)
Intelligent Design
Biology 3201
Notes
1.
Evolution
Unit 4
Page 25 of 26
Chemical Evolution
A theory of evolution created by Oparin – Haldane
They said that organic molecules (the building blocks of life) could develop from
inorganic compounds present on the surface of the early earth.
The early earth had an atmosphere that consisted of no oxygen, but plenty
of hydrogen, Ammonia (NH3), Methane (CH4) and water vapour
(inorganic molecules).
These gases condensed and formed a “primordial soup”.
Energy from lightning and UV radiation caused “organic molecules” to
develop from the inorganic molecules in the soup.
Over time, the organic molecules combined to become an early life form.
Miller – Urey
Two scientists who designed an experiment to prove Oparin – Haldane’s
theory. Here is what they did:
The combined Methane, ammonia, water vapour and hydrogen in a flask
and exposed the gases to an energy source simulating lightning.
The liquid inside the flask changed colour and when examined contained
several organic compounds including amino acids.
ƒ Amino acids make up proteins which make up the structure of
most living things.
2.
Panspermia
A theory that suggests life began “Elsewhere” in the universe and “migrated” to
our planet.
For example, it is believed that life originated from bacterial cells elsewhere and
travelled from outer space to earth on meteorites.
3.
Gaia Hypothesis
Theory put forth by James Lovelock
Idea that “Earth is a “superorganism” called “Gaia”.
The Earth has systems that keep a balance between temperature and
atmosphere.
After life originated on earth, Gaia came “alive” and began to regulate
earth systems.
The systems help provide an environment where life could exist and
survive.
Biology 3201
Notes
4.
Evolution
Unit 4
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Heterotroph Hypothesis
Theory put forth by Oparin.
Said that first “cells” on earth had to be “heterotrophs” that eventually
developed into autotrophs.
Primordial soup existed of organic molecules.
The environment was oxygen poor.
Heterotrophs such as anaerobic bacteria fed on the organic molecules.
The heterotrophs began to release carbon dioxide into the atmosphere. The
heterotrophs developed into autotrophs and began using the carbon dioxide.
The autotrophs began to release O2 into the atmosphere.
This made the atmosphere oxygen rich that could now support life.
5.
Symbiogenesis
Put forth by Lynn Margulis
Theory that attempts to explain the development of Mitochondria and
Chloroplasts as organelles that appear in eukaryotic cells.
Chloroplasts and Mitochondria have their own DNA and come from the
symbiosis (working together) of prokaryotic cells.
Here is how she said eukaryotic organisms may have developed:
An anaerobic bacterium ate but did not digest an aerobic bacterium
(called a guest bacterium)
The guest provided oxygen to the bacterium. The guest bacterium
eventually became a mitochondrion.
Other bacteria ate photosynthesizing bacteria. The
photosynthesizing bacteria became chloroplasts.
6.
Intelligent Design
A Theory that suggests life and mechansisms of life are too complex to have
evolved by chance.
Believed that the generation and evolution of life must have been directed by
some unidentified supernatural intelligence.