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5.4 EVOLUTION
Ms. TRS
5.4.1 - Define evolution
•The cumulative change
in the heritable
characteristics of a
population
or
•The changes in allelic
frequencies in the gene
pool of a population
over time, as a result of
natural selection,
genetic drift, gene flow,
and mutation pressure.
Evidence of Evolution
• 5.4.2 - Outline the evidence for evolution by the fossil record, selective
breeding of domesticated animals and homologous structures
• Fossil record
• Homologous structures
• Selective breeding
Fossils are the
mineralized remains
of organisms that
lived in the past.
The study of fossil
skeletons allows
inferences about
form and function
and clearly
suggests a process
of gradual change
over time.
Selective breeding
Domesticated
breeds have been
developed by
selecting desirable
traits, and
breeding from
them
Selective Breeding
• Man has selectively bred animals and plants for thousands
of years.
• If an animal posses a characteristic that is considered useful
or valuable then this animal is selected for breeding.
• The hope then is that this characteristic will be present in
the next generation and at a higher frequency than before.
In subsequent generations it may even then be possible to
select from an even more advantageous characteristic
The observations of artificial selection (selective breeding)
suggested that natural populations would:
Show phenotypic variation
Be subject to natural selection pressures
There would be selection of those individuals possessing the
advantageous characteristic
Homologous structures: vertebrate
embryos and the pentadactyl limb.
homologous structures: various
different structures sharing the
same fundamental plan
-derived from a similar
embryonic origin
-variations on the basic
structure allow different
functions
adaptive radiation =
permitting exploitation of
different ways of life
suggests divergence from a
common ancestor
a) Humerus
b) Radius
c) Ulna
•In each example the bones are modified and adapted to the
locomotion of the animal
•The fact that the basic shape and position of the bones is
similar suggest that they have a common ancestor
•In the whale there is no real need for the fingers as they can
still swim without them, this could suggest common ancestry
with the other five-fingered organisms
Homologous structures
Homologous Structure?
What structure do these two have in
common?
5.4.3 - State that populations tend to
produce more offspring than the
environment can support
5.4.4 - Explain that the consequence of
the potential overproduction of offspring
is a struggle for survival
5.4.5 - State that members of a species
show variation
5.4.6 - Explain how sexual reproduction
promotes variation in species
5.4.7 - Explain how natural selection
leads to evolution
Natural selection
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Darwin’s theory of Evolution
Overproduction
Competition
Struggle for existence
Survival of the fittest
Natural selection
Populations tend to produce more
offspring than the environment can
support.
Consequence of the potential
overproduction
• Struggle for survival
observation 1: All species have such great potential
fertility that their population size would increase
exponentially if all individuals that are born
reproduced successfully
observation 2: Populations tend to remain stable in
size except for seasonal fluctuations.
observation 3: Environmental resources are limited.
inference 1: Production of more individuals than the
environment can support leads to a competition for
resources like food and space among individuals of a
population, predation, parasitism or natural forces
with only a fraction of offspring surviving each
generation
This is called the struggle for existence
Members of a species show variation.
Sexual reproduction promotes
variation in a species.
Meiosis:
Crossing over of homologous chromosomes during
prophase I results in a recombination of maternal and
paternal alleles within chromosomes
Independent assortment as homologous chromosomes
randomly orient at metaphase I causing a randomized
inheritance of maternal and paternal chromosomes within
gametes
Fertilization:
New combinations of alleles appear during fertilization
As the unique set of haploid alleles in the egg
Combine with the unique set of haploid alleles in the
sperm
• Independent
Assortment
Crossing Over
Natural selection
Those individuals whose inherited
characteristics(variations) best fit them
to their environment are likely to leave
more offspring than less-fit individuals
A fish with a better shaped mouth might be able to feed on
coral that cannot be accessed by other fish, he will have a
better chance of survival into adulthood
A fish mouth could be inadequately adapted and as a result die
of starvation
Natural selection
This unequal ability of
individuals to survive and
reproduce will lead to a gradual
change in a population, with the
inheritance of favorable
characteristics accumulating
over the generations.
5.4.8 - Explain two
examples of evolution in
response to
environmental change;
one must be antibiotic
resistance in bacteria
Antibiotic resistance in bacteria
• Shortly after development of antibiotics (e.g.
penicillin) nearly all bacteria were killed during an
application. Only those who had a gene for
antibiotic resistance survived to reproduce.( 1
resistant bacterium can produce 10000000000
descendants in 24 hours under favourable
conditions!)
• Repeated applications of antibiotics produced, over
time, a greater proportion of individuals with
resistance to the antibiotics
• Antibiotics resistance is the variation that is
selected for
Evolution
Industrial melanism
Peppered moths
During the day the moth rests underneath the
branches of trees and relies on camouflage to protect
it from insect-eating birds
Until 1849 only the speckled variety was observed.
From 1849 (industrial pollution getting worse) until the
late 1960’s the black variety was reported in everincreasing numbers
Speckled form
A single gene controls appearance.
The alleles are - C: black, c: speckled
Trees in unpolluted regions often had growths of
speckled lichen. This lichen was killed off in polluted
areas, causing bark to look much blacker
Black form
Selection pressure: Bird predation? Successful
allele? Black form has more chance of survival in
polluted areas.
General biocide resistance in insects
•Shortly after development of biocides (e.g.
DDT) nearly all insects were killed during an
application except those with a variation
that helped to resist the insecticide.These
survived to reproduce, passing on the gene
to next generation.
•Repeated applications of biocides
produced, over time, a greater proportion of
individuals with resistance to the biocide
•Biocide resistance selected for
Outline two modern examples
where evolution can be
observed. 2 marks
•Change of beak shape in
Galapagos finches
•Resistance to pesticides/antibiotics
•Bird predation on moths
•Heavy metal tolerance in plants
Outline five types of evidence which support
the theory of evolution by natural selection. 6
marks
•Geographic distribution: ring species/other
evidence from geographical distribution
•Biochemistry: cytochrome c/other biochemical
evidence
•Fossils/paleontological: fossilized horse
ancestors/other evidence
•Homologous structures: pentadactyl limb
•Resistance to antibiotics/insecticides/heavy
metal tolerance.
Explain the evidence from homologous anatomical
structures that supports the theory of evolution. 6 marks
•Homologous structures are various different structures
of the same basic plan derived from a similar embryonic
origin
•Variations on the basic structure allow different
functions permitting exploitation of different ways of
life/adaptive radiation
•This suggests divergence from a common ancestor
•Example of a homologous structure is pentadactyl limb
of mammals
•Basic structure of this is the same in a horse, humans,
bats and whales. Humerus, radius, ulna, carpals, meta
carpals and phalanges are there in all.
•variation in the structure is related to different functions
of this organ in these individuals