Transcript Lecture Slides
Chapter 13 How Populations Evolve
PowerPoint ® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Lectures by Chris C. Romero, updated by Edward J. Zalisko
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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.
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• 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 © 2010 Pearson Education, Inc.
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 © 2010 Pearson Education, Inc.
•
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.
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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 • In one modern definition of
evolution
, the genetic composition of a population changes over time.
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1809 Lamarck publishes his theory of evolution.
Darwin begins analyzing his specimens and writing his notebooks on the origin 1830 Lyell publishes Principles of Geology.
1837 of species.
1809 Charles Darwin is born.
1831 –36 Darwin travels around the world on the HMS Beagle.
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.
Green sea turtle in the Galápagos Islands
Figure 13.2
Green sea turtle in the Galápagos Islands
Figure 13.2a
Figure 13.2b
Figure 13.2c
Figure 13.2d
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Darwin’s Cultural and Scientific Context
The Origin of Species
challenged the notion that the Earth was: – Relatively young – Populated by unrelated species © 2010 Pearson Education, Inc.
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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.
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Lamarck and Evolutionary Adaptations
In the mid-1700s, the study of fossils began to take form as a branch of science.
• Naturalist Georges Buffon noted that: – The Earth may be more than 6,000 years old – There are similarities between fossils and living species – Fossil forms might be ancient versions of similar living species © 2010 Pearson Education, Inc.
• Jean Baptiste Lamarck suggested that organisms evolved by the process of adaptation by the inheritance of acquired characteristics, now known to be incorrect.
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•
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.
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Darwin in 1840
Figure 13.3a
HMS Beagle
Figure 13.3b
0 0 Galápagos Islands Pinta PACIFIC OCEAN Fernandina Isabela Genovesa Marchena Equator Santiago Daphne Islands Pinzón Santa Cruz Santa Fe San Cristobal 40 km 40 miles Florenza Española
Figure 13.3c
• On his journey on the
Beagle
, Darwin: – Collected thousands of specimens – Observed various adaptations in organisms © 2010 Pearson Education, Inc.
• Darwin was intrigued by: – The geographic distribution of organisms on the Galápagos Islands – Similarities between organisms in the Galápagos and those in South America © 2010 Pearson Education, Inc.
Figure 13.4a
Figure 13.4b
• 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.
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•
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 © 2010 Pearson Education, Inc.
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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 © 2010 Pearson Education, Inc.
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The Fossil Record
Fossils
are: – Imprints or remains of organisms that lived in the past – Often found in sedimentary rocks © 2010 Pearson Education, Inc.
• 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 © 2010 Pearson Education, Inc.
Figure 13.5
• Paleontologists: – Are scientists that study fossils – Have discovered many transitional forms that link past and present © 2010 Pearson Education, Inc.
Figure 13.6-3
•
Biogeography
Biogeography
is the study of the geographic distribution of species that first suggested to Darwin that today’s organisms evolved from ancestral forms.
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• Many examples from biogeography would be difficult to understand, except from an evolutionary perspective.
• One example is the distribution of marsupial mammals in Australia.
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Common ringtail possum Red kangaroo Australia Koala Common wombat
Figure 13.7
•
Comparative Anatomy
Comparative anatomy
– Is the comparison of body structure between different species – Confirms that evolution is a remodeling process © 2010 Pearson Education, Inc.
•
Homology
is: – The similarity in structures due to common ancestry – Illustrated by the remodeling of the pattern of bones forming the forelimbs of mammals © 2010 Pearson Education, Inc.
Human Cat Whale Bat
Figure 13.8
•
Vestigial structures
: – Are remnants of features that served important functions in an organism’s ancestors – Now have only marginal, if any, importance © 2010 Pearson Education, Inc.
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Comparative Embryology
Early stages of development in different animal species reveal additional homologous relationships.
– For example, pharyngeal pouches appear on the side of the embryo’s throat, which: – Develop into gill structures in fish – Form parts of the ear and throat in humans – Comparative embryology of vertebrates supports evolutionary theory.
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Chicken embryo Pharyngeal pouches Post-anal tail Human embryo
Figure 13.9
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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 © 2010 Pearson Education, Inc.
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
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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.
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(a) The large ground finch (b) The small tree finch (c) The woodpecker finch
Figure 13.11
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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 © 2010 Pearson Education, Inc.
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Observation 1: Overproduction
– All species tend to produce excessive numbers.
– This leads to a struggle for existence.
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Spore cloud
Figure 13.12
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Observation 2: Individual variation
– Variation exists among individuals in a population.
– Much of this variation is heritable.
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Figure 13.13
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Inference: Differential reproductive success (natural selection)
– Those individuals with traits best suited to the local environment generally leave a larger share of surviving, fertile offspring.
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Natural Selection in Action
Examples of natural selection include: – Pesticide-resistant insects – Antibiotic-resistant bacteria – Drug-resistant strains of HIV © 2010 Pearson Education, Inc.
Insecticide application Chromosome with gene conferring resistance to pesticide Survivors Reproduction
Figure 13.14-3
The Process of Science: Does Predation Drive the Evolution of Lizard Horn Length?
•
Observation
: Flat-tailed horned lizards defend against attack by: – Thrusting their heads backward – Stabbing a shrike with the spiked horns on the rear of their skull •
Question
: Are longer horns a survival advantage?
•
Hypothesis
: Longer horns are a survival advantage.
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Killed Live (a) A flat-tailed horned lizard 20 10 Killed Live (b) The remains of a lizard impaled by a shrike 0 Rear horns Side horns (tip to tip) (c) Results of measurement of lizard horns
Figure 13.15
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Prediction
: Live horned lizards have longer horn lengths than dead ones.
•
Experiment
: Measure the horn lengths of dead and living lizards.
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Results
: The average horn length of live lizards is about 10% longer than that of dead lizards.
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Killed Live 20 10 Killed Live 0 Rear horns (c) Results of measurement of lizard horns Side horns (tip to tip)
Figure 13.15c
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 © 2010 Pearson Education, Inc.
Tetrapod limbs Amnion Feathers Lungfishes Amphibians Mammals Lizards and snakes Crocodiles Ostriches Hawks and other birds
Figure 13.16
The Modern Synthesis: Darwinism Meets Genetics
• The
modern synthesis
is the fusion of genetics with evolutionary biology.
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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 © 2010 Pearson Education, Inc.
(a) Two dense populations of trees separated by a lake
Figure 13.17a
(b) A nighttime satellite view of North America
Figure 13.17b
• 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.
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Genetic Variation in Populations
Individual variation abounds in populations.
– Not all variation in a population is heritable.
– Only the genetic component of variation is relevant to natural selection.
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• Variable traits in a population may be: – Polygenic, resulting from the combined effects of several genes or – Determined by a single gene • Polygenic traits tend to produce phenotypes that vary more or less continuously.
• Single gene traits tend to produce only a few distinct phenotypes.
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Figure 13.18
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Sources of Genetic Variation
Genetic variation results from: – Mutations, changes in the DNA of an organism – Sexual recombination, the shuffling of alleles during meiosis © 2010 Pearson Education, Inc.
• For any one gene, mutation alone has little effect on a large population in a single generation.
• Organisms with very short generation spans, such as bacteria, can evolve rapidly with mutations as the only source of genetic variation.
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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.
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• 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 © 2010 Pearson Education, Inc.
• Genotype frequencies: – Can be calculated from allele frequencies – Are symbolized by the expressions
p
2 , 2
pq
, and
q
2 © 2010 Pearson Education, Inc.
Figure 13.19
Allele frequencies
p
0.8
(R)
q
(r) 0.2
R p
0.8
Sperm
r q
0.2
R p
0.8
Eggs
r q
0.2
p2
RR
0.64
pq Rr
0.16
qp rR
0.16 q2
rr
0.04 Genotype frequencies p2
0.64 (RR) 2pq
0.32 (Rr) q2
0.04 (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.
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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.
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• 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 © 2010 Pearson Education, Inc.
INGREDIENTS: SORBITOL, MAGNESIUM STEARATE, ARTIFICIAL FLAVOR, ASPARTAME † (SWEETENER), ARTIFICIAL COLOR (YELLOW 5 LAKE, BLUE 1 LAKE), ZINC GLUCONATE.
† PHENYLKETONURICS: CONTAINS PHENYLALANINE
Figure 13.21
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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.
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• From a genetic perspective evolution can be defined as a generation-to-generation change in a population’s frequencies of alleles, sometimes called
microevolution
.
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•
MECHANISMS OF EVOLUTION
The main causes of evolutionary change are: – Genetic drift – Gene flow – Natural selection © 2010 Pearson Education, Inc.
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Genetic Drift
Genetic drift
is: – A change in the gene pool of a small population – Due to chance © 2010 Pearson Education, Inc.
RR rr Rr RR RR
Only 5 of 10 plants leave offspring
RR rr Rr RR rr
Rr
RR Rr RR Rr
Generation 1 p (frequency of R)
q (frequency of r)
0.7
0.3
Rr rr RR Rr
Generation 2
p q
0.5
0.5
Rr
Only 2 of 10 plants leave offspring
RR RR RR RR RR RR RR RR RR
Generation 3
p q
1.0
0.0
RR
Figure 13.22-3
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The Bottleneck Effect
The
bottleneck effect
: – Is an example of genetic drift – Results from a drastic reduction in population size © 2010 Pearson Education, Inc.
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.
• Cheetahs appear to have experienced at least two genetic bottlenecks in the past 10,000 years.
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Figure 13.24
•
The Founder Effect
The
founder effect
is likely when a few individuals colonize an isolated habitat and represent genetic drift in a new colony.
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• The founder effect explains the relatively high frequency of certain inherited disorders among some small human populations.
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Africa South America Tristan da Cunha
Figure 13.25
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Gene Flow
Gene flow: – Is genetic exchange with another population – Tends to reduce genetic differences between populations © 2010 Pearson Education, Inc.
Figure 13.26
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Natural Selection: A Closer Look
Of all causes of microevolution, only natural selection promotes adaptation.
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Darwinian Fitness
•
Fitness
is the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals.
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Figure 13.27
•
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.
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•
Stabilizing selection
: – Favors intermediate phenotypes – Is the most common © 2010 Pearson Education, Inc.
Original population Original population Evolved population Phenotypes (fur color) (a) Directional selection (b) Disruptive selection (c) Stabilizing selection
Figure 13.28
•
Sexual Selection
Sexual dimorphism
is: – A distinction in appearance between males and females – Not directly associated with reproduction or survival © 2010 Pearson Education, Inc.
•
Sexual selection
is a form of natural selection in which inherited characteristics determine mating preferences.
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(a) Sexual dimorphism in a finch species
Figure 13.29a
(b) Competing for mates
Figure 13.29b
Evolution Connection: The Genetics of the Sickle-Cell Allele
• Sickle-cell disease: – Is a genetic disorder – Affects about one out of every 400 African-Americans • Abnormally shaped red blood cells cause painful and life threatening complications.
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• Heterozygous individuals for the sickle-cell allele: – Do not develop sickle-cell anemia – Are more resistant to malaria • In the African tropics, where malaria is most common, the frequency of the sickle-cell allele is highest. © 2010 Pearson Education, Inc.
Areas with high incidence of malaria Frequencies of the sickle-cell allele 0 –2.5% 2.5
–5.0% 5.0
–7.5% 7.5
–10.0% 10.0
–12.5%
12.5%
Figure 13.30a
Figure 13.30b