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
(see first page of chapter 13)
Consider DDT, the first widely used synthetic insecticide.

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

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
(using caged females w/ pheromones)
%Recaptured
Woodland Melanics Pepper
Urban
Rural
27.5%
6.3%
13.0%
12.5%
This shows a difference but does not prove that birds CAUSED it.



Science is “roll up your sleeves” process…
HBD doesn’t even wear a shirt !!!
;-)
Differential Predation Observations
(freshly killed moths placed on trees and watched)
Woodland
Urban
Rural
# moths eaten by birds
Melanics Pepper
15
164
43
26
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…
Hb A = “N” = normal
Hb S = “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 Hb β: 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

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

or heterosis or hybrid vigor
Malaria case
 Allele Hb S causes sickle-cell anemia when homozygous
 Heterozygotes
(NS)
 are more resistant to malaria than homozygotes
(SS or NN)
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)

homologous structures (vs analogous structures)
Human
Cat
Whale
Figure 13.8
Bat

homologous structures (vs analogous structures)
Human
Cat
Whale
Figure 13.8
Bat

Neo-Darwinism = The Modern Synthesis evidence from
Comparative Embryology (development)

Chicken embryo
Comparative Embryology
Pharyngeal pouches
Post-anal tail
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
Chimpanzee
Human
Gorilla
Orangutan
Gibbon
Old World monkey
Percent of selected DNA sequences that match a chimpanzee’s DNA
92% 96% 100%
Figure 13.10

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

Eurasia
South
America
Africa
India
Madagascar
Antarctica
Laurasia
Figure 14.17

Neo-Darwinism = The Modern Synthesis evidence from Paleontology (fossils)

Neo-Darwinism = The Modern Synthesis evidence from Paleontology: The Fossil Record

Neo-Darwinism = The Modern Synthesis evidence from Vestigial Structures

vestiges, the “scars” of evolution

vestiges, the “scars” of evolution

Neo-Darwinism = The Modern Synthesis evidence from Vestigial Structures

Neo-Darwinism = The Modern Synthesis evidence from Vestigial Structures

 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)


The 3 main causes of evolutionary change are:
• Genetic drift
• Gene flow
• Natural selection (only natural selection is adaptive)

 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.”

e.g. Founder Effect and Bottleneck Effect

 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)

• A change in the gene pool of a small population
• Due to chance

Figure 13.19

Genetic Drift is: A change in the gene pool of a small population, …due to chance
RR
RR
Rr rr
RR
Rr
RR
Rr
RR
Generation 1
p (frequency of R))

0.7
q (frequency of (r)

0.3
Rr
Only 5 of
10 plants leave offspring rr
RR
Rr
RR rr
Rr rr
Rr
Generation \ 2 2 p

0.5
q

0.5
RR
Rr
Only 2 of
10 plants leave offspring
RR
RR
RR
RR
RR
RR
RR
RR
Generation 3 p

1.0
q

0.0
RR
RR
Figure 13.22-3


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 :
• 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 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)

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


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

Original population
Original population
Evolved population
Phenotypes (fur color)
(a) Directional selection (b) Disruptive selection (c) Stabilizing 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.


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 = p 2 + 2pq + q 2 = 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 = p 2 + 2pq + q 2 = 1
( B + r ) 2 = B 2 + 2Br + r 2 = 1
So, p = B = black, the dominant gene
And q = r = red the recessive gene
Shuffle up and deal…

 What is YOUR genotype?
 What is YOUR phenotype?
 What alleles do YOU have?
 What is the population’s gene frequencies for B? for r?

 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 p 2 , 2 pq , and q 2
To refresh our memories, consider the more complex but familiar multipleallele 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.