13 lecture presentation0

Biology and Society:
Persistent Pests
• Mosquitoes and malaria
– In the 1960s, the World Health Organization (WHO) began a campaign
to eradicate the mosquitoes that transmit malaria.
– It used DDT, to which some mosquitoes have evolved resistance.
© 2010 Pearson Education, Inc.

• The evolution of pesticide-resistant insects is just one of the ways
that evolution affects our lives.
• An understanding of evolution informs every field of biology, for
example:
– Agriculture
– Medicine
– Biotechnology
– Conservation biology

CHARLES DARWIN AND THE ORIGIN OF
SPECIES
• Charles Darwin published On the Origin of Species by Means of
Natural Selection, November 24, 1859.
• Darwin presented two main concepts:
– Life evolves
– Change occurs as a result of “descent with modification,” with natural
selection as the mechanism

• Natural selection is a process in which organisms with certain
inherited characteristics are more likely to survive and reproduce
than are individuals with other characteristics.

A Trinidad tree mantid that mimics dead leaves
Figure 13.1a

A leaf mantid in Costa Rica
Figure 13.1b

A flower mantid in Malaysia
Figure 13.1c

• Natural selection leads to:
– A population (a group of individuals of the same species living in the
same place at the same time) changing over generations
– Evolutionary adaptation

1809
Lamarck
publishes
his theory
of evolution.
1830
Lyell publishes
Principles of Geology.
1837
Darwin begins analyzing his
specimens and writing his
notebooks on the origin
of species. 1844
Darwin writes his essay
on the origin of species.
1865
Mendel publishes
papers on genetics.
1858
Wallace sends an
account of his
theory to Darwin.
1859
Darwin publishes
The Origin of Species.
1809
Charles Darwin
is born.
1831–36
Darwin travels
around the world
on the HMS Beagle.
Green sea turtle in the
Galápagos Islands
1800
1870
Figure 13.2

The Idea of Fixed Species
• The Greek philosopher Aristotle held the belief that species are
fixed and do not evolve.
• The Judeo-Christian culture fortified this idea with a literal
interpretation of the Bible and suggested the Earth may only be
6,000 years old.

The Voyage of the Beagle
• Darwin was born on February 12, 1809, the same day that
Abraham Lincoln was born.
• In December 1831 Darwin left Great Britain on the HMS Beagle
on a five-year voyage around the world.
Video: Galápagos Islands Overview

Darwin in 1840
Galápagos
Islands
North
America
South
America
PACIFIC
OCEAN
PACIFIC
OCEAN
ATLANTIC
OCEAN
Pinta
40 miles
40 km0
Florenza
0
Fernandina
Marchena
Genovesa
Equator
Santiago
Daphne Islands
Pinzón
Española
Isabela Santa
Cruz
Santa
Fe San
Cristobal
Great
Britain
Cape of
Good Hope
Europe
Africa
Cape Horn
Tierra del Fuego
Equator
Asia
HMS Beagle
Australia
Tasmania
New
Zealand
Andes
Figure 13.3

Galápagos
Islands
PACIFIC
OCEANPinta
40 miles
40 km0 Florenza
0
Fernandina
Marchena
Genovesa
Equator
Santiago
Daphne Islands
Pinzón
Española
Isabela Santa
Cruz
Santa
Fe San
Cristobal
Figure 13.3c

• On his journey on the Beagle, Darwin:
– Collected thousands of specimens
– Observed various adaptations in organisms

• Darwin was strongly influenced by the writings of geologist
Charles Lyell.
• Lyell suggested that the Earth:
– Is very old
– Was sculpted by gradual geological processes that continue today
• Darwin applied Lyell’s principle of gradualism to the evolution of
life on Earth.

Descent with Modification
• Darwin made two main points in The Origin of Species:
– Organisms inhabiting Earth today descended from ancestral species
– Natural selection was the mechanism for descent with modification

EVIDENCE OF EVOLUTION
• Biological evolution leaves observable signs.
• We will examine five of the many lines of evidence in support of
evolution:
– The fossil record
– Biogeography
– Comparative anatomy
– Comparative embryology
– Molecular biology

The Fossil Record
• Fossils are:
– Imprints or remains of organisms that lived in the past
– Often found in sedimentary rocks

• The fossil record:
– Is the ordered sequence of fossils as they appear in rock layers
– Reveals the appearance of organisms in a historical sequence
– Fits the molecular and cellular evidence that prokaryotes are the
ancestors of all life
Video: Grand Canyon

• Paleontologists:
– Are scientists that study fossils
– Have discovered many transitional forms that link past and present

Biogeography
• Biogeography is the study of the geographic distribution of
species that first suggested to Darwin that today’s organisms
evolved from ancestral forms.

Comparative Anatomy
• Comparative anatomy
– Is the comparison of body structure between different species
– Confirms that evolution is a remodeling process

Molecular Biology
• The hereditary background of an organism is documented in:
– Its DNA
– The proteins encoded by the DNA
• Evolutionary relationships among species can be determined by
comparing:
– Genes
– Proteins of different organisms

Percent of selected DNA sequences
that match a chimpanzee’s DNA
Chimpanzee
100%96%92%
Human
Gibbon
Orangutan
Gorilla
Primate
Old World
monkey
Figure 13.10

NATURAL SELECTION
• Darwin noted the close relationship between adaptation to the
environment and the origin of new species.
• The evolution of finches on the Galápagos Islands is an excellent
example.

(a) The large ground finch
Figure 13.11a

(b) The small tree finch
Figure 13.11b

(c) The woodpecker finch
Figure 13.11c

Darwin’s Theory of Natural Selection
• Darwin based his theory of natural selection on two key
observations:
– All species tend to produce excessive numbers of offspring
– Organisms vary, and much of this variation is heritable

Natural Selection in Action
• Examples of natural selection include:
– Pesticide-resistant insects
– Antibiotic-resistant bacteria
– Drug-resistant strains of HIV
Blast Animation: Natural Selection
Blast Animation: Evidence for Evolution: Antibiotic Resistance in Bacteria

Chromosome with gene
conferring resistance
to pesticide
Insecticide application
Figure 13.14-1

to pesticide
Figure 13.14-2

to pesticide
Reproduction
Survivors
Figure 13.14-3

EVOLUTIONARY TREES
• Darwin saw the history of life as analogous to a tree:
– The first forms of life on Earth form the common trunk
– At each fork is the last common ancestor to all the branches extending
from that fork

Tetrapod
limbs
Amnion
Feathers
Lungfishes
Mammals
Amphibians
Lizards
and snakes
Crocodiles
Hawks and
other birds
Ostriches
Amniotes
Tetrapods
Birds
Figure 13.16

The Modern Synthesis:
Darwinism Meets Genetics
• The modern synthesis is the fusion of genetics with evolutionary
biology.

Populations as the Units of Evolution
• A population is:
– A group of individuals of the same species, living in the same place, at
the same time
– The smallest biological unit that can evolve

• The total collection of alleles in a population at any one time is
the gene pool.
• When the relative frequency of alleles changes over a number of
generations, evolution is occurring on its smallest scale, which is
sometimes called microevolution.

Sources of Genetic Variation
• Genetic variation results from:
– Mutations, changes in the DNA of an organism
– The shuffling of alleles during meiosis

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.

• Alleles can be symbolized by:
– p for the relative frequency of the dominant allele in the population
– q for the frequency of the recessive allele in the population

• Genotype frequencies:
– Can be calculated from allele frequencies
– Are symbolized by the expressions p2
, 2pq, and q2

Allele frequencies
Genotype frequencies
Sperm
Eggs
p = 0.8
(R)
q = 0.2
(r)
p = 0.8
R
q = 0.2
r
RR
p = 0.8
R
q = 0.2
r
p2 = 0.64
rR
qp = 0.16
q2 = 0.04
rr
pq = 0.16
Rr
(RR)p2 = 0.64 q2 = 0.04(rr)
2pq = 0.32
(Rr)
Figure 13.20

• The Hardy-Weinberg formula can be used to calculate the
frequencies of genotypes in a gene pool from the frequencies of
alleles.

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.

• 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),
ARTIFICIAL COLOR
(YELLOW 5 LAKE, BLUE 1
LAKE), ZINC GLUCONATE.
†
PHENYLKETONURICS:
CONTAINS PHENYLALANINE
Figure 13.21

Microevolution as Change in a Gene Pool
• How can we tell if a population is evolving?
• A non-evolving population is in genetic equilibrium, called the
Hardy-Weinberg equilibrium, in which the population gene pool
remains constant over time.

• From a genetic perspective evolution can be defined as a
generation-to-generation change in a population’s frequencies of
alleles, sometimes called microevolution.

MECHANISMS OF EVOLUTION
• The main causes of evolutionary change are:
– Genetic drift
– Gene flow
– Natural selection

Genetic Drift
• Genetic drift is:
– A change in the gene pool of a small population
– Due to chance
Animation: Causes of Evolutionary Change

The Bottleneck Effect
• The bottleneck effect:
– Is an example of genetic drift
– Results from a drastic reduction in population size

Original
population
Figure 13.23-1

Original
population
Bottlenecking
event
Figure 13.23-2

Original
population
Bottlenecking
event
Surviving
population
Figure 13.23-3

• Bottlenecking in a population usually reduces genetic variation
because at least some alleles are likely to be lost from the gene
pool.

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.

South
America
Tristan da Cunha
Africa
Figure 13.25b

Gene Flow
• Gene flow:
– Is genetic exchange with another population
– Tends to reduce genetic differences between populations

Natural Selection: A Closer Look
• Of all causes of microevolution, only natural selection promotes
adaptation.

Darwinian Fitness
• Fitness is the contribution an individual makes to the gene
pool of the next generation relative to the contributions of
other individuals.
Video: Wolves Agonistic Behavior

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

Original
population
Evolved
population Phenotypes (fur color)
Frequency
ofindividualsOriginal
population
(a) Directional selection (b) Disruptive selection (c) Stabilizing selection
Figure 13.28

Frequency of
heterozygotes
Frequency of
homozygotes
for alternate allele
Frequency of
homozygotes
for one allele
Figure 13.UN2

Individual
variation
Overproduction
of offspring
Observations
Natural selection:
unequal reproductive success
Conclusion
Figure 13.UN3

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