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Examples of Evolution by Natural Selection
Microevolution vs. Macroevolution


Microevolution is intraspecific evolution,
evolution WITHIN a species.
Macroevolution is speciation. One species
evolves into a new species.
Examples of Evolution by Natural
Selection
Example #1: Antibiotic Resistance




This is a famous example, known by almost everyone but
rarely called “evolution.”
But it is !!! We hear “resistance develops” or resistance
emerges” etc. In fact, resistance evolves.*
AR is a fine example of very fast evolution AND
A fine example of one way Darwinian evolution is
important to your health and well-being.
*They DO NOT “become immune to the antibiotics.”
This phenomenon is NOTHING like you getting a flu shot!!
Examples of Evolution by Natural
Selection
Example #1: Antibiotic Resistance
AR is the “poster-child” for rapid evolution.*
If we develop a new antibiotic this year and…
a resistant strain of bacteria develops in a London
hospital …



•
•
resistant strains will evolve and be in all London
hospitals in 6 months and…
they will be observed in Hong Kong in two years, i.e.
they will have moved around the Earth in two years.
How does that happen?
*Steven Sterns, Yale U.
Examples of Evolution by Natural Selection
Example #1: Antibiotic Resistance
Examples of Evolution by Natural Selection
Example #2: Pesticide Resistance
Insecticides, Fungicides, Herbicides
Consider DDT, the first widely used
synthetic insecticide.

(see first page of chapter 13)
Examples of Evolution by Natural Selection
Example #2: Pesticide Resistance

Insecticides, Fungicides, Herbicides
Consider DDT, the first widely used synthetic insecticide.

Species Resistant to Insecticides
•
•
•
•
•
•
1948: 14
1956: 69
1970: 224
1976: 364
1984: 447
1989: 504
Example #2: Pesticide Resistance
Herbicide Resistance in 6 Species of Plants in Czech Republic
Examples of Evolution by Natural Selection
Example #3: The Peppered Moth
Biston betularia
Industrial Melanism in a Night-flying Moth
The Peppered Moth, Biston betularia
an example of directional selection
Fig. 18-6a1, p.288
Natural Selection in the Peppered Moth
H.B.D. Kettlewell
Mark and Recapture Experiments
Differential Predation Observations
(freshly killed moths placed on trees and watched)
(using caged females w/ pheromones)
%Recaptured
Woodland Melanics Pepper
Urban
27.5%
13.0%
Rural
6.3%
12.5%
This shows a difference but does not
prove that birds CAUSED it.



Woodland
Urban
Rural
# moths eaten by birds
Melanics
Pepper
15
43
164
26
Science is “roll up
your sleeves”
process…
HBD doesn’t even
wear a shirt !!!
;-)
Industrial melanism is seen in more than 70 species of British moths;
all show patterns similar to that seen in B. betularia.
Evolution by Natural Selection: The Peppered Moth
Left: Kettelwell, 1956
Right: Grant et.al. 1998
Grant's comments on these maps: "The maps show a before-after comparison of the geographic distribution of melanic phenotypes in peppered
moth populations in Britain based on Kettlewell's 1956 survey (left map) and that conducted 40-years later (1996) by my colleagues and me (right
map). The black segments of the pie charts indicate the percentage of melanics at the various locations. Clearly melanism has declined everywhere
it was once common." (Grant, personal communication, February 11, 2002)
The source publication for these maps: Grant, B. S., Cook, A. D. , Clarke, C. A., and Owen, D. F. 1998. Geographic and temporal variation in the
incidence of melanism in peppered moth populations in America and Britain. Journal of Heredity 89:465-471.
Examples of Evolution by Natural Selection
Example #4: Sickle-cell Anemia and Malaria
Example #4: Sickle-cell Anemia and Malaria
Okay, let’s simplify it…
HbA = “N” = normal
HbS = “S” = sickle cell
NN = “normal”
Ns = “normal but carrier”
sN = “normal but carrier”
ss = sickle-cell anemia
The Genetic Basis of Sickle Cell Anemia
HbA vs Hbβ: Everyone has HbA (141), and Hb-non-A (146)”
HbS is a mutant form of HbA
The Genetic Basis of Sickle Cell Anemia
The Distribution of the Sickle-Cell Gene
less than 1 in 1,600
1 in 400-1,600
1 in 180-400
1 in 100-180
1 in 64-100
more than 1 in 64
Fig. 18-13b, p.293
Malaria: the Plasmodium parasite
Sickle cell anemia is a genetic disease of the blood.
Malaria is parasitic disease of the blood.
What is the relationship between these two diseases?
The Distribution of Falciparum Malaria
Fig. 18-13a, p.293
Geographic Distribution of Malaria vs. Sickle-cell Anemia
Sickle-Cell Trait:
Heterozygote Advantage
or heterosis or hybrid vigor
 Allele
HbS
causes
sickle-cell anemia
when homozygous
 Heterozygotes (NS)
 are more resistant to
malaria than
homozygotes (SS or NN)
Malaria case
Sickle-cell trait
less than 1 in 1,600
1 in 400-1,600
1 in 180-400
1 in 100-180
1 in 64-100
more than 1 in 64
What Is Our View of Darwin’s Idea Today?
The Modern Synthesis: Darwinism Meets Genetics


To his credit, his idea has withstood the scrutiny of about 150
years of scientific testing.
But a lot has happened in 150 years.
What Is Our View of Darwin’s Idea Today?
Neo-Darwinism = The Modern Synthesis
Neo-Darwinism @ Darwin + Modern Genetics
What Is Our View of Darwin’s Idea Today?
Neo-Darwinism = The Modern Synthesis
Neo-Darwinism @ Darwin + Modern Genetics
What Is Our View of Darwin’s Idea Today?
Neo-Darwinism = The Modern Synthesis
Neo-Darwinism @ Darwin + Modern Genetics
What Is Our View of Darwin’s Idea Today?
Neo-Darwinism = The Modern Synthesis
Neo-Darwinism @ Darwin + Modern Genetics
What Is Our View of Darwin’s Idea Today?
Neo-Darwinism = The Modern Synthesis
Neo-Darwinism @ Darwin + Modern Genetics
What Is Our View of Darwin’s Idea Today?
Neo-Darwinism = The Modern Synthesis
Neo-Darwinism @ Darwin + Modern Genetics
And also every other branch of biology that has grown since 1859
and contributes to our understanding of Darwin’s idea, i.e. all of
them. Especially...
All




the “Comparatives”
Comparative Anatomy (morphology)
Comparative Embryology (development)
Comparative Ethology (behavior)
Comparative Biochemistry (molecular biology: proteins and DNA)
Biogeography (where do they live and why?)
Paleontology (the fossil record)
Vestigial
Structures (the “scars” of evolution)
Neo-Darwinism = The Modern Synthesis
evidence from
Comparative Anatomy (morphology)
Comparative Anatomy
homologous structures (vs analogous structures)
Human
Cat
Bat
Whale
Figure 13.8
Comparative Anatomy
homologous structures (vs analogous structures)
Human
Cat
Bat
Whale
Figure 13.8
Comparative Embryology
Neo-Darwinism = The Modern Synthesis
evidence from
Comparative Embryology (development)
Comparative Embryology
Pharyngeal
pouches
Post-anal
tail
Chicken embryo
Human embryo
Figure 13.9
Neo-Darwinism = The Modern Synthesis
evidence from Molecular Biology
(Comparative Biochemistry)
Neo-Darwinism = The Modern Synthesis
evidence from Comparative Biochemistry
(= comparative molecular biology)
What mutation could cause isoleucine (Ile) to change to phenylalanine (Phe)?
And what mutation can change Leucine (Leu) to Arginine (Arg)
Primate
Percent of selected DNA sequences
that match a chimpanzee’s DNA
92%
96%
Chimpanzee
Human
Gorilla
Orangutan
Gibbon
Old World
monkey
Figure 13.10
100%
Neo-Darwinism = The Modern Synthesis
evidence from Comparative Biochemistry
We can calculate rates of mutation particularly in very stable
genes or pseudogenes and use them as clocks
Cytochrome C: yeast, wheat, human
Neo-Darwinism = The Modern Synthesis
evidence from Biogeography
Cenozoic
Present
Eurasia
65
Africa
South
America
India
Madagascar
Antarctica
Paleozoic
251 million years ago
Mesozoic
135
Laurasia
Figure 14.17
Neo-Darwinism = The Modern Synthesis
evidence from Paleontology (fossils)
Neo-Darwinism = The Modern Synthesis
evidence from Paleontology: The Fossil Record
Fossil
Record
Neo-Darwinism = The Modern Synthesis
evidence from Vestigial Structures
The Recurrent Laryngeal Nerve
vestiges, the “scars” of evolution
The Recurrent Laryngeal Nerve
vestiges, the “scars” of evolution
Neo-Darwinism = The Modern Synthesis
evidence from Vestigial Structures
Neo-Darwinism = The Modern Synthesis
evidence from Vestigial Structures
Does Evolution occur by
mechanisms other than
natural selection?
 YES.


Evolution can…
be slow or fast;
and it can be helpful, harmful or neutral.
Does Evolution occur by mechanisms
other than natural selection?
OK, how about this question…
Does Evolution not occur?
What’s necessary for equilibrium?
 NO mutation
 NO gene flow
 NO genetic drift
 NO nonrandom mating (i.e. totally random mating)
 NO natural selection
 A large population.
ALL
OF THESE CONDITIONS OCCURRING SIMULTANEOUSLY IS UNLIKELY!
Analyzing Gene Pools



The gene pool is a reservoir from which the next
generation draws its genes.
Alleles in a gene pool occur in certain frequencies.
When thinking about evolution, think gene pool !
Evolution is a change in the genetic make-up of a POPULATION (gene pool)
Does Evolution occur by
mechanisms other than
natural selection?

The 3 main causes of evolutionary change are:
• Genetic drift
• Gene flow
• Natural selection (only natural selection is adaptive)
Does Evolution occur by
mechanisms other than
natural selection?
 Let’s
look at Genetic Drift.
 Just consider the two words:
Natural Selection
vs.
 Genetic Drift

Genetic Drift

Genetic drift is:
• A change in the gene pool of a small population
• Due to chance events.
• Compare the words: “drift” vs “selection.”
Genetic Drift
e.g. Founder Effect and Bottleneck Effect
Genetic Drift
 Oreaster

reticularum in Bahamas…
Non-random mating
 Examples



from textbook…
Non-random mating (small population of
flowers)
Bottleneck Effect (cheetahs)
Founder Effect (humans on Tristan da Cahuna)
The Caribbean Cushion Star
• A change in the gene pool of a small population
•
Due to chance
Flower Example from Text
Figure 13.19
Genetic Drift is:
A change in the gene pool of a small
population, …due to chance
rr
RR
RR
Only 5 of
10 plants
leave
offspring
Rr
rr
Rr
Rr
Rr
RR
Rr
Generation 1
p (frequency of R))  0.7
q (frequency of (r)  0.3
RR
rr
RR
RR
rr
Rr
RR
Only 2 of
10 plants
leave
offspring
RR
RR
RR
RR
RR
RR
RR
RR
RR
Rr
Rr
Generation \22
RR
Generation 3
p  0.5
q  0.5
p  1.0
q  0.0
Figure 13.22-3
RR
The Bottleneck Effect

The bottleneck effect:
• Is an example of genetic drift
• Results from a drastic reduction in population size
often due to some catastrophic event.
Original
population
Bottlenecking
event
Surviving
population
The Bottleneck Effect

The bottleneck effect:
• Is an example of genetic drift
• Results from a drastic reduction in population size
• The hunting of large cats like the cheetah


Bottlenecking in a population usually reduces
genetic variation because at least some alleles are
likely to be lost from the gene pool.
Cheetahs appear to have experienced at least two
genetic bottlenecks in the past 10,000 years.
The Founder Effect


The founder effect is likely when a few individuals
colonize an isolated habitat and represent genetic
drift in a new colony.
The founder effect explains the relatively high
frequency of certain inherited disorders among
some small human populations.
• Huntington’s Disease around Lake Maracaibo Venezuela
• Hereditary blindness on Tristan da Cuhana
• Galapagos species (drift + selection)
Founder Effect
Africa
South
America
Tristan da
Cunha
Figure 13.25
Gene Flow

Gene flow:
• Is genetic exchange with another population
• Tends to reduce genetic differences between
populations
Three General Outcomes of
Natural Selection

Directional selection:
• Shifts the phenotypic “curve” of a population
• Selects in favor of some extreme phenotype

Disruptive selection:
• can lead to a balance between two or more contrasting
phenotypic forms in a population.

Stabilizing selection:
• Favors intermediate phenotypes
• Is the most common
Frequency
of individuals
Original
population
Phenotypes (fur color)
Original
population
Evolved
population
(a) Directional selection
(b) Disruptive selection
(c) Stabilizing selection
Sexual Selection

Sexual dimorphism is:
• A distinction in appearance between males and
females
• Not directly associated with reproduction or survival

Sexual selection is a form of natural selection
in which inherited characteristics determine
mating preferences.
(a) Sexual dimorphism in
a finch species
(b) Competing for mates
Figure 13.29
(a) Sexual dimorphism in a finch species
Figure 13.29a
(b) Competing for mates
Figure 13.29b
Population Genetics and Health Science


The Hardy-Weinberg formula can be used to
calculate the percentage of a human population
that carries the allele for a particular inherited
disease.
Go over this in book on your own.
END OF CHAP 13
ON TO CHAP 14
Old slides

PKU:
• Is a recessive allele that prevents the breakdown of
the amino acid phenylalanine
• Occurs in about one out of every 10,000 babies born
in the United States
INGREDIENTS: SORBITOL,
MAGNESIUM STEARATE,
ARTIFICIAL FLAVOR
ASPARTAME† (SWEETENER),
INGREDIENTS: SORBITOL,
MAGNESIUM STEARATE,
ARTIFICIAL FLAVOR
† PHENYLKETONURICS:
CONTAINS PHENYLALANINE
The Hardy-Weinberg formula can be
used to calculate the frequencies of
genotypes in a gene pool from the
frequencies of alleles.
(p+q)2 = p2 + 2pq + q2 = 1
Let’s do a simple analysis of a gene pool:
 Set



these conditions:
Just one trait, (let’s say fur color)
With just two alleles, B + r
And one dominant (B) and the other recessive (r)
Let’s say the genes exist the in the gene pool at 50-50.
The Hardy-Weinberg formula can be
used to calculate the frequencies of
genotypes in a gene pool from the
frequencies of alleles.
(p+q)2 = p2 + 2pq + q2 = 1
(B+r)2 = B2 + 2Br + r2 = 1
So, p = B = black, the dominant gene
And q = r = red the recessive gene
Shuffle up and deal…
Hardy Weinberg
 What
is YOUR genotype?
 What is YOUR phenotype?
 What alleles do YOU have?
 What is the population’s gene frequencies
for B? for r?
Hardy-Weinberg Equilibrium
 OK,
mate (randomly). Give a gamete to
anyone else until everyone has two.
 Has anything changed in the gene pool?
 Has
anything changed?
 Has the population evolved?

Genotype frequencies:
• Can be calculated from allele frequencies
• Are symbolized by the expressions p2, 2pq, and q2
To refresh our memories, consider the more complex
but familiar multiple-allele Human ABO Blood Types…
Neither A nor B is dominant to the other, o is recessive.
A, B, O are the three alleles
AA, Ao, BB, Bo, AB, oo are the six genotypes
Type A, Type B, Type AB and Type O are the four
phenotypes.