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BIG IDEA I
The process of evolution drives
the diversity and unity of life.
Enduring Understanding 1.A
Change in the genetic makeup of a population over time is evolution.
Essential Knowledge 1.A.1
Natural selection is a major mechanism of evolution.
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Essential Knowledge 1.A.1: Natural selection is a
major mechanism of evolution.
• Learning Objectives:
– (1.1) The student is able to convert a data set from a
table of numbers that reflect a change in the genetic
makeup of a population over time and to apply
mathematical methods and conceptual understandings
to investigate the cause(s) and effect(s) of this change.
– (1.2) The student is able to evaluate evidence provided
by data to qualitatively and quantitatively investigate
the role of natural selection in evolution.
– (1.3) The student is able to apply mathematical
methods to data from real or simulated populations to
predict what will happen to the population in the future.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Overview: Endless Forms Most Beautiful
• A new era of biology began in 1859
when Charles Darwin published On
The Origin of Species By Means of
Natural Selection
• The Origin of Species focused
biologists’ attention on the great
diversity of organisms, whereby
Darwin noted that current species
are descendants of ancestral
species
• Evolution can be defined by
Darwin’s phrase descent with
modification, and can be viewed as
both a pattern and a process
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Darwin’s Two Major Points from Origin of Species
1. The manuscript presented evidence that many species of
organisms presently inhabiting the Earth are descendants
of ancestral species (common descent)
2. The manuscript proposed a mechanism for the
evolutionary process (natural selection)
 a population’s allele frequency can change over
generations if individuals that possess certain heritable
traits leave more offspring than others
 results in evolutionary adaptation – accumulation of
inherited characteristics that enhance organisms’ ability
to survive and reproduce in specific environments
 evolution – change over time in genetic composition of
a population and could eventually lead to new species
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-1
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Fig. 22-UN1
Observations
Individuals in a population
vary in their heritable
characteristics.
Organisms produce more
offspring than the
environment can support.
Inferences
Individuals that are well suited
to their environment tend to leave
more offspring than other individuals
and
Over time, favorable traits
accumulate in the population.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Natural Selection & Reproductive Success
FITNESS is measured as
REPRODUCTIVE success.
Natural selection is differential
success in reproduction - it
results from the interaction
between individuals that vary in
heritable traits and their
environment.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-12
(a) A flower mantid
in Malaysia
(b) A stick mantid
in Africa
Natural Selection: A Summary
1. Overpopulation - more organisms are born than can survive
2. Variation within a population - there will be many variation
for different traits among individuals
3. Competition within the population - individuals will compete
for survival: food, mates, shelter, etc.
4. Survival of the Fittest - those with traits best suited to the
environment will be more likely to survive
5. Reproduction - individuals that survive will pass their traits
on to the next generation
6. Adaptive Evolution – over time, specialized traits that
enhance survival and reproduction accumulate in a
population.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Hardy-Weinberg equation can be used to test
whether a population is evolving.
• Mathematical approaches are used by scientists to
calculate changes in allele frequency, providing
evidence for the occurrence of evolution in a
population.
– A population is a localized group of individuals
capable of interbreeding and producing fertile
offspring
– A gene pool consists of all the alleles for all
loci in a population
– A locus is fixed if all individuals in a population
are homozygous for the same allele
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Population Genetics and Hardy-Weinberg
• Hardy-Weinberg Principle – states that allele frequencies
tend to remain constant in populations unless something
happens OTHER THAN Mendelian segregation and
sexual recombination.
– This situation in which allele frequencies remain constant is called
genetic equilibrium.
– If allele frequencies do not change, the population will not evolve!
• Hardy-Weinberg is a mathematical model that describes
the changes in allele frequencies in a population:
– Allows us to predict allele and genotype frequencies in subsequent
generations (testable).
– Allows us to determine whether or not a population is evolving
(mathematically supported evidence of evolution).
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Calculating Allele Frequencies
• By convention, if there are 2 alleles at a locus,
p and q are used to represent their frequencies
– p = frequency of dominant allele in
population
– q = frequency of recessive allele in
population
• The frequency of all alleles in a population will
add up to 1
– For example, p + q = 1
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Hardy-Weinberg Principle
• Model Assumptions: conditions required to
maintain genetic equilibrium from generation to
generation:
1. Randomly Mating Population
2. Large Population Size (n>100)/No Genetic Drift
3. No Immigration or Emigration/Restrict Gene Flow
4. No Mutations
5. No Natural Selection
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Hardy-Weinberg Principle
• Let p= frequency of allele A
• Let q= frequency of allele a
• Let p2= frequency of genotype AA
• Let 2pq= frequency of genotype Aa
• Let q2= frequency of genotype aa
• Law says, given assumptions, that within 1 generation of
random mating, the genotype frequencies are found to be in
the binomial distribution p2+2pq+q2=1 (genotype
frequencies) and p+q=1 (allele frequencies)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Applying the Hardy-Weinberg Principle
• The allele for the ability to roll one’s tongue is
dominant (R) over the allele for the lack of this
ability (r).
• In a population of 500 individuals, 25% show the
recessive phenotype. How many individuals
would you expect to be homozygous dominant
and heterozygous?
– The equation: p2 + 2pq + q2 = 1
– Therefore, p + q = 1
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Adaptive Evolution in Changing Environments
• A diverse gene pool is important for the survival of
a species in a changing environment.
• Environments can be more or less stable or
fluctuating, and this affects evolutionary rate and
direction; different genetic variations can be
selected in each generation.
• An adaptation is a genetic variation that is favored
by natural selection and is manifested as a trait
that provides an advantage to an organism in a
particular environment.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Genes & Variation
•
While developing his theory of evolution, Darwin worked
under a serious disadvantage – he did not know how
heredity worked
•
Without understanding heredity, Darwin was unable to
explain 2 important factors:
1. The source of variation central to his theory
2. How hereditable traits were passed from one generation to the
next
•
Today, genetics, molecular biology, and evolutionary
theory work together to explain how inheritable variation
appears and how natural selection operates on that
variation (i.e. how evolution takes place).
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Mutation and sexual reproduction produce the genetic
variation that makes evolution possible.
• Two processes, mutation and sexual
reproduction, produce the variation in gene
pools that contributes to differences among
individuals
– Variation in individual genotype leads to
variation in individual phenotype
– Not all phenotypic variation is heritable
– Natural selection can only act on variation with
a genetic component
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 23-2
(a)
(b)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Mutation
• Mutations are changes in the nucleotide sequence of DNA
• Mutations cause new genes and alleles to arise
• Only mutations in cells that produce gametes can be
passed to offspring
A A A
A A
A A A
A A A
a a
A a A
A
a
T=0
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
T=1
Point Mutations
• A point mutation is a change in one base in a gene
• The effects of point mutations can vary:
– Mutations in noncoding regions of DNA are often
harmless
– Mutations in a gene might not affect protein production
because of redundancy in the genetic code
– Mutations that result in a change in protein production
are often harmful
– Mutations that result in a change in protein production
can sometimes increase the fit between organism and
environment
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Types of Point Mutations
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Mutations That Alter Gene Number or Sequence
• Chromosomal mutations that delete, disrupt, or
rearrange many loci are typically harmful
– Duplication of large chromosome segments
is usually harmful
– Duplication of small pieces of DNA is
sometimes less harmful and increases the
genome size
– Duplicated genes can take on new
functions by further mutation
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Types of Chromosomal Mutations
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Sexual Reproduction
• Sexual reproduction can shuffle existing
alleles into new combinations
• In organisms that reproduce sexually,
recombination of alleles is more
important than mutation in producing the
genetic differences that make adaptation
possible
• Three mechanisms contribute to the
shuffling of alleles during sexual
reproduction:
• Crossing over
• Independent assortment of alleles
• Fertilization
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Natural selection is NOT the only mechanism
responsible for evolution.
• Although natural selection is usually the
major mechanism for evolution, genetic
variation in populations can occur through
other processes:
– Mutation, genetic drift, sexual selection and
artificial selection can all contribute to the
evolution of a population.
– Inbreeding, small population size, nonrandom
mating, the absence of migration, and a net lack of
mutations can lead to loss of genetic diversity.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Genetic Drift
• The smaller a sample, the greater the chance
of deviation from a predicted result.
• Genetic drift describes how allele frequencies
fluctuate unpredictably from one generation to
the next.
• Genetic drift tends to reduce genetic variation
through losses of alleles.
• REAL WORLD EXAMPLES OF GENETIC DRIFT:
1. The Bottleneck Effect
2. The Founder Effect
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 23-8-3
CR CR
CR CR
CW CW
CR CW
CR CW
CR CR
CW CW
CR CR
CR CW
CR CR
CR CW
CR CW
Generation 1
p (frequency of CR) = 0.7
q (frequency of CW ) = 0.3
CW CW
CR CW
CR CR
CR CR
CR CR
CW CW
CR CR
CR CW
CR CR
CR CR
CR CR
CR CR
CR CR
CR CR
CR CR
CR CW
Generation 2
p = 0.5
q = 0.5
CR CR
CR CR
Generation 3
p = 1.0
q = 0.0
BIG IDEA I
The process of evolution drives
the diversity and unity of life.
Enduring Understanding 1.A
Change in the genetic makeup of a population over time is evolution.
Essential Knowledge 1.A.2
Natural selection acts on phenotypic variations in populations.
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Essential Knowledge 1.A.2: Natural selection acts
on phenotypic variations in populations.
• Learning Objectives:
– (1.4) The student is able to evaluate data-based
evidence that describes evolutionary changes in the
genetic makeup of a population over time.
– (1.5) The student is able to connect evolutionary
changes in a population over time to a change in the
environment.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Remember: The environment acts as a selecting
agent for natural selection.
• The environment is always changing, there is no
“perfect” genome, and a diverse gene pool is necessary
for the long-term survival of species.
– Genetic variations within a population contribute to the
diversity of the gene pool.
– Changes in genetic information may be silent, or result
in a new phenotype (positive, negative or neutral).
– The interaction of the environment and the phenotype
determines the fitness of the phenotype.
– Thus, the environment does NOT direct changes in
DNA, but acts upon existing that occur through
random changes in DNA.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Evolution and the Environment
• Natural selection does not create new traits,
but edits or selects for traits already present in
the population
• The local environment determines which traits
will be selected for or selected against in any
specific population
• Because environments change, they act as
selective mechanisms on populations
– Illustrative Example: peppered moth
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Evolution and the Environment
Peppered Moth
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Effect of Phenotypic Variations
• Some phenotypic variations significantly increase
or decrease fitness of the organism and the
population.
• Illustrative Examples:
– Peppered Moth
– DDT Resistance in Insects
– Sickle Cell Anemia
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Evolution of Insecticide Resistance
1. By spraying crops with poisons
to kill insects, humans have
unwittingly favored the
reproductive success of insects
with inherent resistance to
poisons.
2. Resistant individuals survive
and reproduce, passing the
gene for resistance to offspring.
3. Additional applications of the
same insecticide will be less
effective, and the frequency of
resistant insects in the
population will grow.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Red blood cells are able to transport oxygen
because they are filled with a protein called
hemoglobin, which picks up oxygen in the lungs and
drops it off where it is needed in tissues and organs.
A mutated version in one of the hemoglobin genes
leads to Sickle Cell Anemia by changing the
hemoglobin protein in such a way that it tends to
clump up into long chains inside red blood cells.
Instead of maintaining the usual flexible disc-like
shape that enables them to squeeze through even
the tiniest blood vessels, the red blood cells of
people with the disease twist into stiff crescents that
are not efficient at transporting oxygen.
"Sickled" red blood cells can clog small blood
vessels, preventing oxygen from making it to certain
parts of the body. The condition is life-threatening.
Molecular Basis of Sickle Cell Disease
In the DNA, the mutant
template strand (top) has
an A where the wild type
template has a T.
The mutant mRNA has a
U instead of an A in one
codon.
The mutant (sickle cell)
hemoglobin has a valine
(Val) instead of a glutamic
acid (Glu).
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Heterozygous Advantage & Sickle Cell Anemia
•
In the United States, one in every 500 African-American births and one
out of every 1,000 to 1,400 Hispanic births is affected by Sickle Cell
Anemia. Another two million Americans carry the sickle cell trait.
•
As devastating as the disease can be, it turns out there is a reason
Sickle Cell Anemia is so common and has NOT been “weeded out” of
the human population.
•
Usually a DNA change that causes a serious disease quickly gets
pushed out of a population's gene pool. But researchers have found
that the version of the gene that causes Sickle Cell Anemia has been
around for thousands of years.
•
That observation, and the fact that this version is mainly found in
people with ancestors who lived relatively recently in Africa, the
Mediterranean, India, or the Middle East, led scientists to wonder if the
Sickle Cell Anemia-causing version of the gene offers some kind of
benefit to people living in those regions.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Sickle Cell and Resistance to Malaria
•
That benefit turned out to be
resistance to malaria. Malaria is
caused by parasites that multiply
inside of human red blood cells.
Because the disease can only be
transferred from person to person by
mosquitoes, it is confined to areas of
the world where the insects thrive.
•
Every year malaria infects more than
300 million people and kills more than
a million, particularly young children.
•
Carriers of the sickle cell trait are to a
large extent resistant to malaria.
Compared to non-carriers, they have
approximately 1/10 the risk of dying
from infection by the most deadly
species of malaria parasite.
•
Nevertheless, carriers are not
completely protected from the disease
and experts recommend that they still
take precautions against malaria.
Heterozygous Advantage & Sickle Cell Anemia
• Over the years, carriers living in malaria-ridden locales
would have had a survival benefit compared to noncarriers, allowing them to live longer and have more
children.
• This benefit is what evolutionary biologists call
"heterozygote advantage," and it explains why the sickle
cell trait has persisted in areas where malaria is common.
• The price for the carriers' advantage, though, is that some
of their children are born with Sickle Cell Anemia.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 23-17
Mapping Malaria
&
Sickle Cell Disease
Frequencies of the
sickle-cell allele
0–2.5%
Distribution of
malaria caused by
Plasmodium falciparum
(a parasitic unicellular eukaryote)
2.5–5.0%
5.0–7.5%
7.5–10.0%
10.0–12.5%
>12.5%
Human Impact on Genetic Variation
• Humans can impact variation in other species.
• Illustrative Examples:
– Artificial Selection
– Overuse of Antibiotics
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-9
Terminal
bud
Lateral
buds
Cabbage
Brussels sprouts
Flower
clusters
Leaves
Kale
Cauliflower
Stem
Wild mustard
Flowers
and stems
Broccoli
Kohlrabi
Human Impact on Genetic Variation
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Fig. 22-UN2
Inquiry Challenge
Mosquitoes resistant to the pesticide DDT first sppeared in India in 1959, but
now are found throughout the world.
a. Graph the data in the table above.
b. Examine the graph and hypothesize why the percentage of mosquitoes resistant
to DDT rose rapidly.
c. Suggest an explanation for the global spread of DDT resistance.
Fig. 22-UN3
BIG IDEA I
The process of evolution drives
the diversity and unity of life.
Enduring Understanding 1.A
Change in the genetic makeup of a population over time is evolution.
Essential Knowledge 1.A.3
Evolutionary change is also driven by random processes.
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Essential Knowledge 1.A.3: Evolutionary change is
also driven by random processes.
• Learning Objectives:
– (1.6) The student is able to use data from
mathematical models based on the Hardy-Weinberg
equilibrium to analyze genetic drift and effects of
selection in the evolution of specific populations.
– (1.7) The student is able to justify data from
mathematical models based on the Hardy-Weinberg
equilibrium to analyze genetic drift and the effects of
selection in the evolution of specific populations.
– (1.8) The student is able to make predictions about the
effects of genetic drift, migration and artificial selection
on the genetic makeup of a population.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Remember: The process of evolution drives the
diversity and unity of life.
• Evolution is a change in the genetic makeup
of a population over time with natural
selection its major driving mechanism.
–
Darwin’s theory, supported by evidence from many
disciplines, states that inheritable variations occur in
individuals in a population.
–
Due to competition for limited resources, individuals
with more favorable variations are more likely to
survive and produce more offspring, thus passing
traits to future generations.
–
Individuals do not evolve, but rather populations evolve.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Remember: Natural selection is not the only mechanism
responsible for evolution.
• Although natural selection is usually the
major mechanism for evolution, genetic
variation in populations can occur through
other processes:
– Mutation, genetic drift, sexual selection and
artificial selection can all contribute to the
evolution of a population.
– Inbreeding, small population size, nonrandom
mating, the absence of migration, and a net lack of
mutations can lead to loss of genetic diversity.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Overview: The Smallest Unit of Evolution
• Focusing on evolutionary change in
populations, we can define evolution on its
smallest scale, called microevolution.
– Microevolution involves evolutionary changes below
the species level; changes in allele frequencies in a
population over generations.
– Our focus in this section will be to understand that
natural selection is not the only cause of
microevolution.
– The other two mechanisms include genetic drift and
gene flow.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Genetic Drift
• The smaller a sample, the greater the chance of
deviation from a predicted result. Genetic drift is a
nonselective process occurring in small
populations.
• Genetic drift describes how allele frequencies
fluctuate unpredictably from one generation to the
next.
• Genetic drift tends to reduce genetic variation
through losses of alleles – and this reduction of
genetic variation within a given population can
increase the differences between populations of
the same species.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Founder Effect
http://bcs.whfreeman.com/thelifewire/content/chp24/2402002.html
Sample of
Original Population
Descendants
Founding Population A
Founding Population B
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The Bottleneck Effect
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Fig. 23-10
Pre-bottleneck Post-bottleneck
(Illinois, 1820) (Illinois, 1993)
Range
of greater
prairie
chicken
(a)
Location
Population
size
Percentage
Number
of alleles of eggs
per locus hatched
Illinois
1,000–25,000
5.2
93
<50
3.7
<50
Kansas, 1998
(no bottleneck)
750,000
5.8
99
Nebraska, 1998
(no bottleneck)
75,000–
200,000
5.8
96
Minnesota, 1998
(no bottleneck)
4,000
5.3
85
1930–1960s
1993
(b)
Effects of Genetic Drift: A Summary
1. Genetic drift is significant in small populations
2. Genetic drift causes allele frequencies to
change at random
3. Genetic drift can lead to a loss of genetic
variation within populations
4. Genetic drift can cause harmful alleles to
become fixed
5. Genetic drift can facilitate inbreeding – which
leads to further reduction in variation
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Gene Flow
• Natural selection and genetic drift are not the
only phenomena affecting allele frequencies.
• Allele frequencies can also change by gene
flow, the transfer of alleles into or out of a
population.
– This transfer of alleles is due to the
movement of fertile individuals or their
gametes (migration).
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Gene Flow in Humans
• Humans today move much more freely about
the world than in the past.
• As a result, mating is more common between
members of populations that previously were
isolated.
• The result is that gene flow has become an
increasingly important agent of evolutionary
change in human populations.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 23-12
70
60
MINE
SOIL
NONMINE
SOIL
NONMINE
SOIL
50
Prevailing wind direction
40
30
20
10
0
20
0
20
0
20
40
60
80
100
120
Distance from mine edge (meters)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
140
160
Gene Flow
• Gene flow can increase the fitness of a
population
• Insecticides have been used to target
mosquitoes that carry West Nile virus and
malaria
• Alleles have evolved in some populations that
confer insecticide resistance to these
mosquitoes
• The flow of insecticide resistance alleles into a
population can cause an increase in fitness
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Remember: Mutation and sexual reproduction are
responsible for the variation seen in populations.
• Mutation:
– Point Mutations: silent; missense; nonsense
– Chromosomal: deletion; duplication; inversion;
translocation
• Sexual Reproduction
– Crossing Over
– Independent Assortment
– Fertilization
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Remember: In addition to natural selection, genetic
drift and gene flow can lead to evolution (non-adaptive).
• Genetic Drift: when chance events lead to unpredictable
fluctuations in allele frequencies from one generation to the next.
–
Effects are most pronounced in small populations.
–
Reduces genetic variation through random loss of alleles.
–
Illustrative Examples: Founder Effect/Darwin’s Finches & Bottleneck
Effect/Greater Prairie Chicken
• Gene Flow: the transfer of alleles from one population to another.
–
Tends to reduce the genetic differences between populations.
–
If extensive enough…can result in neighboring populations combining into a
single common gene pool.
–
Illustrative Examples: gene flow in humans; gene flow in bent grass near
copper mines; insecticide resistance in mosquitos that transmit West Nile
and malaria.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Natural selection is the only mechanism that consistently
causes adaptive evolution.
• Differential success in reproduction results in certain
alleles being passed to the next generation in greater
proportions
• Only natural selection consistently results in adaptive
evolution
• Natural selection brings about adaptive evolution by
acting on an organism’s phenotype
• The phrases “struggle for existence” and “survival of
the fittest” are misleading as they imply direct
competition among individuals
• Reproductive success is generally more subtle and
depends on many factors
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Directional, Disruptive, and Stabilizing Selection
http://bcs.whfreeman.com/thelifewire/content/chp23/2302001.html
• Three modes of selection:
– Directional selection favors individuals at one
end of the phenotypic range
– Disruptive selection favors individuals at both
extremes of the phenotypic range
– Stabilizing selection favors intermediate
variants and acts against extreme phenotypes
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 23-13a
Original population
Phenotypes (fur color)
Original population
Evolved population
(a) Directional selection
Fig. 23-13b
Original population
Phenotypes (fur color)
Evolved population
(b) Disruptive selection
Fig. 23-13c
Original population
Phenotypes (fur color)
Evolved population
(c) Stabilizing selection
The Key Role of Natural Selection in Adaptive
Evolution
• Natural selection increases the frequencies of
alleles that enhance survival and reproduction
• Adaptive evolution occurs as the match between
an organism and its environment increases
• Because the environment can change, adaptive
evolution is a continuous process
• Genetic drift and gene flow do not consistently
lead to adaptive evolution as they can increase or
decrease the match between an organism and its
environment
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
BIG IDEA I
The process of evolution drives
the diversity and unity of life.
Enduring Understanding 1.A
Change in the genetic makeup of a population over time is evolution.
Essential Knowledge 1.A.4
Biological evolution is supported by scientific evidence
from many disciplines, including mathematics.
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Essential Knowledge 1.A.4: Biological evolution is supported by
scientific evidence from many disciplines, including mathematics.
• Learning Objectives:
–
(1.9) The student is able to evaluate evidence provided by data
from many scientific disciplines that support biological evolution.
–
(1.10) The student is able to refine evidence based on data from
many scientific disciplines that support biological evolution.
–
(1.11) The student is able to design a plan to answer scientific
questions regarding how organisms have changed over time
using information from morphology, biochemistry and geology.
–
(1.12) The student is able to connect scientific evidence from
many disciplines to support the modern concept of evolution.
–
(1.13) The student is able to construct and/or justify mathematical
models, diagrams or simulations that represent processes of
biological evolution.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Direct Evidence for Evolution
•
Evolution is supported by an overwhelming amount
of scientific evidence from geographical, geological,
physical, chemical and mathematical applications.
•
New discoveries continue to fill the gaps identified by
Darwin in The Origin of Species.
•
Two examples provide direct evidence for natural
selection:
1.
the effect of differential predation on guppy
populations;
2.
and the evolution of drug-resistant HIV
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-13
EXPERIMENT
Predator: Killifish; preys
mainly on juvenile
guppies (which do not
express the color genes)
Experimental
transplant of
guppies
Pools with
killifish,
but no
guppies prior
to transplant
Guppies: Adult males have
brighter colors than those
in “pike-cichlid pools”
Predator: Pike-cichlid; preys mainly on adult guppies
Guppies: Adult males are more drab in color
than those in “killifish pools”
RESULTS
12
Number of
colored spots
12
10
8
6
4
2
0
Source
population
Transplanted
population
10
8
6
4
2
0
Source
population
Transplanted
population
The Evolution of Drug-Resistant HIV
• The use of drugs to combat HIV selects for
viruses resistant to these drugs
• HIV uses the enzyme reverse transcriptase to
make a DNA version of its own RNA genome
• The drug 3TC is designed to interfere and
cause errors in the manufacture of DNA from
the virus
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-14
100
Patient
No. 1
Patient No. 2
75
50
Patient No. 3
25
0
0
2
4
6
Weeks
8
10
12
Evidence for Evolution
•
Evidence that the diversity of life is a product of evolution pervades
every research field of biology. Molecular, morphological and genetic
information of existing and extinct organisms add to our understanding
of evolution:
–
Fossil Record Evidence
–
–
Succession of Fossil Forms
Comparative Anatomy
– Anatomical Homologies
–
–
Embryological Homologies
–
Molecular Homologies
Biogeography
–
Geographic Distribution of Species
–
Continental Drift
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Evidence for Evolution
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
How Rocks and Fossils Are Dated
• Sedimentary strata reveal the relative ages of
fossils:
–
In relative dating, the order of rock strata is used to determine
the relative age of fossils. Older specimens are found in deeper
layers of strata.
• The absolute ages of fossils can be determined by
radiometric dating
–
Radiometric dating uses the decay of radioactive isotopes to
determine the age of the rocks or fossils.
–
It is based on the rate of decay, or half-life of the isotope (the
time required for half the parent isotope to decay).
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-17
Morphological Homologies
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Homologous structures are those found in different species that are
similar and result from common ancestry.
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Bat
Fig. 22-18
Comparative Embryology
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
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Human embryo
Vestigial Structures
The skeletons of
some snakes retain
vestiges of the
pelvis and leg bones
of walking
ancestors.
We would not
expect to see these
structures if snakes
had an origin
separate from other
vertebrate animals.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Molecular Homologies
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Convergent Evolution
• Although organisms that are closely related
share characteristics because of common
descent, distantly related organisms can
resemble one another for a different reason:
– Convergent evolution is the evolution of similar, or
analogous, features in distantly related groups.
– Analogous traits arise when groups independently
adapt to similar environments in similar ways.
– Convergent evolution does not provide information
about ancestry!
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Homologous v. Analogous Structures
• Homologous structures
are similar structures
occurring in different
species that are believed to
be derived from a common
ancestor.
• Analogous structures are
similar structures occurring
in different species that are
believed to be the result of
convergent evolution
(similar environmental
pressures).
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-20
Sugar
glider
NORTH
AMERICA
AUSTRALIA
Flying
squirrel
Biogeography
• Darwin’s observations of biogeography, the geographic
distribution of species, formed an important part of his
theory of evolution
– Islands have many endemic species that are often
closely related to species on the nearest mainland or
island
– Earth’s continents were formerly united in a single
large continent called Pangaea, but have since
separated by continental drift
– An understanding of continent movement and modern
distribution of species allows us to predict when and
where different groups evolved
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The Geographic Distribution of Species
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings