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Natural Selection
Natural Selection –
“Survival of the Fittest”
• Survive : When things
around you die and
you remain alive
• Fitness: Any
adaptation which
enhances survival
(Ex: Strength,
Immunity, Mental
Ability, Camouflage
(ability to blend)
Charles Darwin
British Naturalist
1809 -1882
The Origin of
Species through
Natural Selection
I have called this principle, by which each slight variation, if useful,
is preserved, by the term Natural Selection.
—Charles Darwin from "The Origin of Species"
Natural Selection
Factors of Evolution
• 1) Individual species vary.
• 2) Some variations are genetic
• 3) More individuals are produced than
reproduce.
• 4) Organisms best adapted to their
environment survive and pass on their traits
to their offspring.
Ecological Niche
• Niche: The “place
where and organism
fits” in the world. An
organism’s space in
the environment
Competition:
• Competition: The
struggle for food,
space (territory) or
reproduction
Predator – Prey relationship
• Predator : Organisms
which stalk and eat
another organism in
order to stay alive.
• Prey: Organism
which is eaten
Predator – Prey relationship
• Predator : Organisms
which stalk and eat
another organism in
order to stay alive.
• Prey: Organism
which is eaten
Reproduction
• Reproduction:
Organisms which
survive pass on their
adaptation traits
(fitness factors)
• Pass on favorable
phenotypes.
Camouflage
• Organisms which blend
into the environment
have greater survival
value
• 1) Cryptic coloration:
Blend with background
Katydid – leaves,
Peppered moths –
industrial melanism
Camouflage
• Organisms which blend
into the environment
have greater survival
value
• 1) Cryptic coloration:
Blend with background
Katydid – leaves,
Peppered moths –
industrial melanism
Cryptic Coloration
Countershading
Camouflage
2) Warning coloration:
Bright distinctive
colors. Ex:
California newt,
Ladybugs – red;
Bumble bee, wasp –
banded warning
Warning Coloration
Camouflage
3) Batesian mimicry:
Where a palatable
(edible) mimic
resembles and
unpalatable model.
Ex: Bumble bees –
Robber flies (H-bee) ;
Monarch vs Viceroy
Environment:
• Environment: Organism’s
surroundings. Anything
other than genes which
influences the expression
of traits (phenotype)
Organisms either adapt,
die, or leave new
environments.
Environmental Factors
Sunlight
Temperature
Precipitation
Soil
Pressure
Pollution
Tides
Salinity
Mutations
• Mutations: May be
caused by natural
agents. Nearly always
harmful. Raw materials
upon which natural
selection operates.
• Some make no difference
• Some are useful (to
us).Ex: Ancon sheep,
Seedless grapes, navel
oranges, Delicious
apples.
Mutations
• Mutations: May be
caused by natural
agents. Nearly always
harmful. Raw materials
upon which natural
selection operates.
• Some make no difference
• Some are useful (to
us).Ex: Ancon sheep,
Seedless grapes, navel
oranges, Delicious
apples.
Environmental restraints
• Any factors which
control the populations
Ex: Water in the desert,
predators, disease, food
source.
• Extinction: When all
the species of a
population die out
Factors of Evolution
• 1) Individual species vary.
• 2) Some variations are genetic
• 3) More individuals are produced than
reproduce.
• 4) Organisms best adapted to their
environment survive and pass on their traits
to their offspring.
Evolution
• Evolution: The
process of change over
a long period of time
producing varyingly
different organisms.
– Species: Genetically
diverse organisms that
mate freely in nature
and produce fertile
offspring.
• genetically diverse –
chromosomal
differences between
species (DNA)
Charles Darwin
British Naturalist
1809 -1882
I have called this principle, by which each slight variation, if useful,
is preserved, by the term Natural Selection.
—Charles Darwin from "The Origin of Species"
Inheritable Mutations
Charles Darwin
British Naturalist
1809 -1882
On the Origin of
Species through
Natural Selection
I have called this principle, by which each slight variation, if useful,
is preserved, by the term Natural Selection.
—Charles Darwin from "The Origin of Species"
b
The Wallace Line (or Wallace's Line) is a boundary that separates
the zoogeographical regions of Asia and Australasia. West of the
line are found organisms related to Asiatic species; to the east,
mostly organisms related to Australian species. The line is named
after Alfred Wallace.
Charles Darwin
British Naturalist
1809 -1882
I have called this principle, by which each slight variation, if useful,
is preserved, by the term Natural Selection.
—Charles Darwin from "The Origin of Species"
Factors of Evolution
• 1) Individual species vary.
• 2) Some variations are genetic
• 3) More individuals are produced than
reproduce.
• 4) Organisms best adapted to their
environment survive and pass on their traits
to their offspring.
Natural Selection
Forms of Selection
1) Stabilizing – Selection
is geared for the
average individuals.
Extremes are removed
2) Directional – Selection
for the most beneficial
trait for an environment
3) Disruptive – Selection
for the two extremes of
traits
Forms of Selection
•
•
•
Stabilizing – Selection is
geared for the average
individuals. Extremes are
removed
Directional – Selection for
the most beneficial trait
for an environment
Disruptive – Selection for
the two extremes of traits
Forms of Selection
•
•
•
Stabilizing – Selection is
geared for the average
individuals. Extremes are
removed
Directional – Selection for
the most beneficial trait
for an environment
Disruptive – Selection for
the two extremes of traits
Forms of Selection
•
•
•
Stabilizing – Selection is
geared for the average
individuals. Extremes are
removed
Directional – Selection for
the most beneficial trait
for an environment
Disruptive – Selection for
the two extremes of traits
Evidence for Evolution
• Direct – Observable
– If you could watch
organisms change for
several generations.
• Ex: Resistant bacteria
and insects to
antiobiotics and
pesticides
Indirect Evidence
• Evidence from dead
organisms or
comparisons
A) Inheritance
• Artificial selection:
Plant and animal
breeders select what
should live or die to
suit specific purposes.
B) Geographic distribution
• Isolations of
populations show
distinct variations
• Isolation : Separation
of populations by
natural barriers
• Divergent populations:
Formed by the
splitting up of original
species by some
barrier
Allopatric speciation
• In allopatric speciation, an
ancestral population is
geographically isolated,
resulting in the evolution of
separate species largely due to
genetic drift.
• The additive effect of
differences due to genetic drift
can eventually result in
behavioral isolation (refusal to
mate) if the two groups were to
meet again in the future.
• If they refused to interbreed,
they would be considered
separate species.
Genetic Drift
• Random events which
cause a change in
allele (gene) frequency
Ammospermophilus harrisi
–Harris’s antelope
South Rim
Ammospermophilus leucurus
– White tailed antelope squirrel
North Rim
Allopatric speciation
•
Allopatric speciation due to geographic separation of the Grand Canyon.
Harris's antelope squirrel (Ammospermophilus harrisi) inhabits the
canyon's south rim (left). Just a few miles away on the north rim (right)
lives the closely related white-tailed antelope squirrel (Ammospermophilus
leucurus). Another example is the Tassel-eared Squirrel, where Abert's
Squirrel (Sciurus aberti) lives on the south rim and the Kaibab Squirrel
(Sciurus aberti kaibabensis) lives on the north rim.
•
Sympatric speciation
• Sympatric speciation
involves speciation
without a geographic
barrier.
• One example of sympatric
speciation is polyploidy, found
more often in plants.
• Polyploidy occurs when a
failure of meiosis increases the
number of chromosome sets to 3N
or more. At this point, the two
"cousin" species can no longer
mate with each other.
C) Reproductive Isolation
D) Fossils
• Remains of organisms
from the past. Show
the change of structure
and from through time
E) Homology
• Presence of common
patterns of structure.
• Ex: Bones in
vertebrate forelimbs,
wings, flippers – same
bones
Homologous Structures in Vertebrates
Vestigial organs
• Lost function (organs)
• Ex: Appendix; hind
limbs in whales,
python; wings – kiwi,
cormorant, penquin
Homology
• Divergence –
Descendants are more
different
• Convergence –
Unrelated organisms –
Analagous – similar
characteristics in
similar environment
F) Embryology
• Studies of early stages.
Much like the
evolutionary history of
species
F) Embryology
• Studies of early stages.
Much like the
evolutionary history of
species
G) Biochemistry
• Analysis of amino
acid sequences.
Different species have
different sequences of
Amino Acids in
Cytochrome C
(Electron transport
chain proteins)
G) Biochemistry
• Similar DNA is found
in the same species.
Fewer DNA
differences are found
in closely related
organisms
Hardy-Weinberg Principle
• Used to assess whether
natural selection is occurring
• States that the frequencies of
alleles and genotypes in a
population will remain the
constant from generation to
generation provided only
Mendelian segregation and
crossing over occur
Hardy-Weinberg Principle
• Used to assess whether
natural selection is occurring
• States that the frequencies of
alleles and genotypes in a
population will remain the
constant from generation to
generation provided only
Mendelian segregation and
crossing over occur
Hardy-Weinberg Principle
• Conditions for HardyWeinberg:
1) No mutations
2) Random mating
3) No natural selection
4) Extremely large population
size
5) No gene flow ( movement
of alleles into or out of
population)
Hardy-Weinberg
Hardy-Weinberg
• Under Hardy-Weinberg equilibrium,
allele and genotype frequencies remain
constant over generations. The allele
frequencies are described by
• p + q = 1, where p is the dominant
allele frequency and q is the recessive
allele frequency.
• The genotype frequencies are described
by p2 + 2pq + q2 = 1, where p2 and q2 are
frequencies of the homozygous genotypes
and 2pq is the frequency of the
heterozygous genotype.
Hardy Weinberg
p = the frequency of the dominant allele (represented here by A)
q = the frequency of the recessive allele (represented here by a)
For a population in equilibrium:
p + q = 1.0 ( the sum of the frequencies of both alleles is 100 %)
(p + q)2 = 1
so
p2 + 2pq + q2 = 1
The three terms of this binomial expansion indicate the frequencies of the three
genotypes:
p2 = frequency of AA (homozygous dominant)
2pq = frequency of Aa (heterozygous)
q2 = frequency of aa (homozygous recessive)