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HowPopulationsEvolve
Objectives
Introduction
Describe five adaptationsthat help blue-footed boobies survive.
Evidenceof Evolution
13.1
13.1
13.1
13.2
13.2
13.3
Briefly describethe history of evolutionarythought.
Explain how Darwin's voyageon the Beagleinfluencedhis thinking.
Describe the ideasand eventsthat resultedin Darwin's 1859book.
Explain how fossilsform, notingexamplesof eachprocess.
Explain how the fossil record providessomeof the sftongestevidenceof evolution.
Explain how biogeography,comparativeanatomy,comparativeembryology,and molecular biology documentevolution.
Darwin'sTheoryand the ModernSynthesis
13.4 Describe Darwin's assumptions
in developingthe conceptof naturalselection.
13.4 Explain how artificial selectionsupportsnatural selection.
L3.5 Describe two examplesof naturalselectionthat are known to occur.Note three key
points about how natural selectionworks.
13.6 Define a populationand a species.
13.6 Explain the significanceof the modernsynthesis.
13.7 Explain how microevolutionoccurs.
L3.8, 13.9 Explain the significanceof Hardy-Weinbergequilibrium to natural populationsand in
public-health science.
13.10 Describe the five conditionsrequiredfor Hardy-Weinbergequilibrium.
13.11 Explain how the bottleneckeffect, the founder effect, geneflow, and mutation influence
microevolution.
13.12 Explain how natural selectionresultsfrom changesin geneticequilibrium.
Variation and Natural Selection
13.13 Explain why only somevariationis heritable.Explainhow geneticvariationis measured.
13.14 Explain how mutation and sexualrecombinationproducegeneticvariation.
13.14 Explain why multiple-drug "cochails" are more likely to be effective againstHW than
single-drugtreatments.
13.15 Explain how geneticvariationis maintainedin populations.
13.16 Explain what is meantby neutralvariation.
13.17 Explain why geneticbottlenecksthreatenthe survival of certain species.
13.1E Define Darwinian fitness.Explainwhy "survivalof the fittest" can be misleading.
13.19 Describethe threegeneraloutcomesof naturalselection.
13.20 Define and compareintrasexualselectionand intersexualselection.
13.21 List four reasonswhy natural selectioncannotproduceperfection.
13.22 Explain why antibioticresistance
hasevolved.
r20
Chapter 13 How PopulationsEvolve
l2l
KeyTerms
evolutionary adaptation
evolution
fossil
descentwith modification
paleontologist
fossil record
biogeography
comparativeanatomy
homologous structure
comparativeembryology
molecular biology
natural selection
artificial selection
population
population genetics
modern synthesis
species
gene pool
microevolution
Hardy-Weinberg
equilibrium
genetic drift
bottleneck effect
founder effect
gene flow
mutation
polymorphic
cline
heterozygoteadvantage
neutral variation
Darwinian fitness
stabilizing selection
directional selection
diversifying selection
sexualdimorphism
WordRoots
bio- : life; geo- the Earth (biogeography:the study of the past andpresentdistributionof species)
resultingfrom a sharedancestry)
homo- = like, resembling(homology:similarity in characteristics
muta- : change(rnutation:a changein the DNA of genesthat ultimatelycreatesgeneticdiversity)
paleo- = ancientQtaleontology.'the scientific stttdy of fossils)
poly- : many;morph- : form (polymorphism:the coexistenceof trpoor more distinctforms of individuals in the samepopulation)
LectureOutline
Introduction Clown,Fool, or SimplyWell-Adapted?
A. Review:Evolution is the central theme of biology. Evolutionary adaptation is a universalcharacteristicof living things (seeModule 1.6).
NOTE: More than any other idea in biology, evolutionarytheory servesto tie the disci"Nothing in biology makessenseexceptin the light of
pline together.T. Dobzhansky:
evolution."
B. If you look at any organismcritically, you are first struckby the differencesfrom other
organisms.
1. Further observationoften reveals that an organism'sfeaturesshow somerelationship
to where the organismlives and what it does in its environment.
2. The blue-footedbooby has enormouswebbedfeet, a nostril that can closeunder
water,preventingwater from entering the lungs, a gland that secretssalt from consumedseawater, and a torpedolike body-all adaptationsthat makelife on the sea
feasible(Figure 13.0A and B).
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Instructor's Guideto TextandMedia
I. Evidence of Evolution
Module 13.1 A seavoyagehelpedDarwin framehis theory of evolution.
andhow they fit the particularconditionsof
A. Awarenessof eachorganism'sadaptations
its environmenthelpsus appreciatethe naturalworld (Figure 13.1A).
held variousviews.Anaximander(about2500yearsago) sugB. Early Greek philosophers
gestedthat life arosein waterand that simplerforms precededmore complexforms of
life. On the otherhand,Aristotle,who stronglyinfluencedlater thinkers,believedthat
specieswere fixed and did not evolve.
tradition that all specieswere
C. This latter view was advancedby the Judeo-Christian
createdin a singleact of creationabout6000yearsago.
that Earthwasmuch older and raisedthe possibilitythat
D. Buffon (mid-1700s)suggested
althoughhe later arguedagainstthis
different speciesarosefrom commonancestors,
point.
Following naturaldisasters,somespecies
NOTE: Buffon alsobelievedin catastrophism:
die off, while populationsof others(alreadypresentin lower numbers)increasein numbersto becomemoredominantthan theyhadbeen.
E. Lamarck(early 1800s)was the first to stronglysupportthe idea of evolution,but he
believedthe mechanismfor changewasthe inheritanceof acquiredcharacteristics.
F. Born in 1809,Darwinjoined the crew of the surveyingship Beagleas a naturalistfor a
voyagein 1831(Figure13.18).
world-encircling
G. Comparisonsof SouthAmericanfossilswith living speciesthereand fossilselsewhere,
Islands,made
and observationsof organismsand their distributionson the GalSpagos
on him.
particularlysffongimpressions
H. Darwin was influencedby Lyell's Principlesof Geology,which promotedthe idea of
continual,gradual,consistentgeologicalchange.
I.
and his
After his retum, Darwin beganwork on an essayto documenthis observations
new theory of evolution.
J. In the mid-1850sWallaceconceivedessentiallythe sametheory basedon his observaof both their works were
tions in Indonesia.He contactedDarwin,andpresentations
madeto the scientificcommunityin 1858.
K. Darwin's On the Oigin of Speciesby Meansof Natural Selectionwas publishedin
argumentfor natural selection,backedby consid1859and containsa well-constructed
erableevidence.He usesthe phrase"descentwith modificationr" which encapsulates
the conceptof evolution.
L. Darwin's view of evolution:The historyof life is like a tree, with multiple branching
from the baseof the trunk to the tips of the branches.Specieson a given branch are
more closely interrelatedthan relatedto specieson other branches.
Module 13.2 The studyof fossilsprovidesstrongevidencefor evolution.
A. Hard parts, suchas skeletonsand shells,remainafter other organic matter has decomposed.Such partsfossilizeeasily@gure 13.24).
of organicmaterials(Figure 13.28).
B. Petrifiedfossilsform by the slow mineralization
C. Fossilizedmoldsof organismsform whena coveredareadecaysand fills in with other
sediment(Figure 13.2C).
D. Somefossils, suchas thoseof leaves,retainremnantsof organicmatterwith molecular
fragmentsthat can be analyzed(Figure I3.2D).
Chapter 13 How Populations Evolve
t?3
E. Organismstrappedin treeresincanbe fossilizedintact,within the fossilizedamber,
protectedfrom decompositionby bacteriaand fungi (Figure 13.28).
The "Ice Man" found in 1991was preservedin
Other mediahavepreservedorganisms.
ice some5000yearsago (Figure13.2F).
G. The fossil record is an arrayof fossilsappearingwithin the layersof sedimentary
of waterbornesediments.Sedimenrocksform from accumulations
rocks.Sedimentary
tary depositsoccurin strata.Eachlayer containsfossilsof organismsamongthe
deposits,with youngerstrataon top of older strata(Figure 13.2G).
H. The fossil recordshowsan historicalsequenceof organismsfrom the oldestknown
appearance
fossils,prokaryotes,datingfrom =3.5 billion years,throughthe subsequent
forms-a
that
intermediate
steps
to
modern
sequence
through
many
on
of eukaryotes,
has an overall patternof changefrom simple to more complexforms.
wherebylinks are seenbetweenextinct organismsand species
NOTE: Sucha sequence,
predicted
by evolutionarytheory Gigure I3.2H). One of the best docualive today,is
mentedseriesis the evolutionof modernhorses.
Preview:The fossil recordchroniclesmacroevolution(Module 15.1).
Module 13.3 A massof evidencevalidatesthe evolutionaryview of life.
A. Biogeographymakesobservationsabout the distribution of different but obviously
relatedlife forms aroundthe world and in neighboringgeographicalregions.Island
forms aremost similar to forms found on the closestmainland,ratherthan thosefound
on ecologicallysimilarbut moredistantislands.
B. Comparativeanatomyof homologousstructures (Figure 13.34). For example,all
mammalshave the samebasic limb structure.
Preview:Module 15.11.
C. Comparative embryologr showsthat different organismsgo through similar embryonic
stages.For example,evidencethat all vertebratesevolvedfrom a common ancestoris
that all havean embryonicstagein which gill pouchesappearin the throat region.
NOTE: In addition to pharyngealgill pouches,vertebrates,along with all chordates,
also havein commonthe presenceof, at somepoint in their life cycle, a notochord
(a cartilaginoussupportingrod), a dorsal hollow nerve cord (spinal cord), and a
post-analtail.
the universalityof the geneticcode (Module 10.8),the
D. Molecular biolory demonstrates
in proteins such as hemoglobin,and the presence
conservationof amino acid sequences
genes
in
very
different species(Module tl.lz).
homeotic
of very similar
E. The picture shownby the fossil record is supportedby other observations(biochemical,
cellular)of existinglife forms (Figure13.38).
II. Darwin's Theory and the Modern Synthesis
Module 13.4 Darwin proposednatural selectionas the mechanismof evolution.
Review:Evolution as an explanationfor the unity and diversity of life was first
discussedin Module 1.6.
A. Darwin observedthat speciestend to produceexcessivenumbersof offspring, that the
expressionof traits variesamongthe individuals of a population,and that many of
thesetraits are heritable.
B. EnglisheconomistThomasMalthus'sessaydiscussedthe inevitablehumansuffering
resultingfrom populationsgrowing faster than suppliesof resources.
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Instructor's Guide to Text and Media
C. Darwin had personalknowledgeof andinterestin artificial selection(Figure 13.44, B)
and comparedthe resultsof artificial selectionto the variationseenamongclosely
relatedspecies(Figure 13.4C).
D. Tlvo importantpoints can be drawn from Darwin's theory of natural selection:
of heritabletraits to
1. Ancestral speciesgaverise to the diverselife forms by transfer
"descent
with modification."
offspringthat bestpromotereproduction.He called this
2. Over vast amountsof time, the gfadualaccumulationof changesin the characteristics amongthe individualsin a populationoccurs.
Module 13.5 Connection:Naturalselectionresultsin evolutionaryadaptations.
A. Two good examplesof the effectsof the processcan be seenin the mantid.In both
cases,new populationshaveresulted,but not new species(Figure 13.5A).
B. Natural selectionis a work in progressandhas been documentedover 100times.A
frighteningcasethat is frequentlyrepeatedis the responseof insectsto insecticides.
Those that have the predispositionfor resistancewill srrvive and passon this trait (a
gene)to their offspring(Figure 13.58).
preview:The sameconceptwill be discussed
with bacteriaand the resistanceto antibiotic therapy(Module 13.22).
C. Natural selectionis regional and timely. Populationstend to evolve in responseto local
environmentalconditions during one time period. A particular adaptationmay be pointless in the contextof otherlocalesor times.
D. Significantevolutionarychangecan occurin very short periodsof time.
Module 13.6 Populationsare the units of evolution.
A. A poputation is a group of individual organismsliving in the sameplace at the same
time.
B. Evolution is measuredas the changein frequencyof a given characteristicwithin a
of generations.
populationover a succession
C. Darwin realized this, but he did not know about the geneticmechanisms.
D. During the 1920spopulation geneticswas combined with Darwinian principles into a
comprehensivetheory of evolution known as the modenn synthesis.
E. Central to this synthesisis the sexualspeciesconcept. A sexualspeciesis a group of
populationswhose individuals have the potential to interbreedand producefertile offrp.iog. A given sexualspecieshas an overall range, with concentrationsof individuals
in local populations.
NOTE: This is the sameas the biological speciesconcept introducedin Chapter 14.
Preview:Sincethe sexual(biological)speciesconceptconcernsactuallyor potentially
interbreedingpopulations,it is difficult to apply it to the fossil record.Another species
conceptthat is more readily applied to the fossil record is the evolutionaryspecies
concept.
F. Opportgnitiesfor breedingamong populationsof the samespeciesvary, dependingon
the speciesand on the extentof isolationof the populations.
Modute 13.7 Microevolutionis changein a population'sgene pool over time'
Review:The basic conceptsof Mendeliangenetics(Chapter9)'
A. A population's gene pool consistsof all the alleles in all the individuals making up the
population.
Chapter 13 How Populations Evolve
125
by two or more allelesacrossa population,and individB. Most geneloci are represented
(of
for
carrying
two allelescanbe homozygousor heterozygous
most eukaryotes)
uals
the locus.
C. During microevolution,the relativefrequenciesof the allelesgovemingcharacteristics
change.For example,thoseinsectswith a genethat confersresistanceto an insecticide
will outnumberthoseinsectswithout this particulargene.Thus,the allele frequencyfor
insecticideresistancewill be higherin fields sprayedwith insecticidethan in untreated
fields.
Module 13.8 The genepool of a nonevolvingpopulationremainsconstantover generations.
NOTE: This exampleis entirely arbitrary and will work with any numbers.Have students verify this fact by trying other examples.
A. Use the exampleof a hypotheticalpopulationof 500 blue-footedboobies.Nonwebbed
feet (WW or Ww) are dominantover webbed feet (ww), and a single gene (alleles
I4zand w) governsthe characteristic:320 have WW,160 have Ww and 20 have
lrw genotypes.
B. The Hardy-Weinbergequationshowsthat allele frequenciesare stablein a population
not undergoingmicroevolution:p2 + Zpq * q' : 1. That is, the populationis madeup
genotypes(2pq) * homozyof: homozygousdominantgenotypes@\ * heterozygous
:
| Q.
gous recessivegenotypes(q'). Also note that p
NOTE: If you have the patienceit may be worth the effort of taking your students
through the derivationof the Hardy-Weinbergequation.Using the examplegiven here:
There are only two alleles of this particular gene,thus their frequenciesmust sum to I
wwis qx q:
(p + q: 1).Theprobability
of WW isp X p: p2itheprobabilityof
q2i there are two ways of being heterozygous,Ww andwlt thus the frequencyof the
heterozygoteis 2pq. Continuing,many of your studentswill be familiar with the FOIL
method from their math classes;have them apply it to the following: p + q : 1; since
q ) ( p* q ) = l . F o l l - i n g t h i s g i v e s u s p 2Z+p q + q 2 : l .
1x I :l(p+
C. The frequenciesof WW,Ww, andww in the first generationare0.64, 0.32, andO.04.
Since blue-footedboobiesare diploid, there are 1000alleles in the population, and their
frequenciesatep : 0.80 w andq : o.2o w (Figure13.88).
D. If random matingsoccur betweenvarious membersof this population,then the laws of
probability will predictthe geneticmakeupof the next generation(seeModule 9.7).
E. On average,the next generationwill have p x p llrflz individuals (: 0.64), (p x q) +
(q x p) IUwindividuals(2pq : 0.32, since thereare two ways to getpq in a zygote,
dependingon whetherthe q is in the sperm or in the egg), and q x q ww individuals
(: 0.M) (Figure 13.8C)'The allele frequenciesremainthe same.
Module 13.9 Connection:The Hardy-Weinbergequationis usefulin public healthscience.
A. Estimating frequenciesof harmful alleles amongthe population at large helps public
health scientistsassessand prioritize their efforts.
B. For example,if PKU occursin one out of 10,000babies(q2 : 0.0001),then q : 0.01,
: 0.0198.
p : O.99,and2pq (the frequencyof carrier heterozygotes)
NOTE: This exercisecan be usedwith any of the frequenciesof genesfrom Table 9.9.
Module 13.L0 Five conditionsare requiredfor Hardy-\ileinberg equilibrium.
NOTE: Hardy-Weinbergequilibrium rarely exists in natural populations(in this senseit
the assumptionsbehindit
can be viewedas a control,Module 1.3), but understanding
how populationsevolve.
gives us a basisfor understanding
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Instructor's Guide to Tbxtand Media
A. The populationis very large.
B. The populationis isolated(no migrationof individuals,or gametes,into or out of the
population).
NOTE: No geneflow (Module13.11).
C. Mutationsdo not alter the genepool.
D Mating is random.
E. All individualsare equalin reproductivesuccess(no naturalselection).
(Modules13.11,13.18)
NOTE: No fitnessdifferences
Module 13.L1 There are severalpotentialcausesof microevolution.
NOTE: Approach this by asking your studentsto identify situationsthat will violate the
conditionslisted in Module 13.10.
A. Genetic drift is a changein a genepool of a small populationdue to chance.The
effect of a loss of individuals from a populationis much gleater when there are fewer
individuals. The bottleneck effect is geneticdrift resultingfrom a disasterthat reduces
populationsize (suchas the exampleof the elephantseals;Figure 13.11A,B). The
founder effect is geneticdrift resulting from colonizationof a new areaby a small
number (even one) of individuals (likely importantin the evolution of animalsand
plants on the GaldpagosIslands).Another good exampleof the founder effect is
the high rate of retinitis pigmentosaamongthe residentsof Tristan da Cunha
(Figure13.11C).
NOTE: Genetic drift is evolution by samplingerror.
B. Gene flow is a gain or loss of alleles from a populationdue to immigration or emigration of individualsor gametes.
C. Mutations are rare events,but they do occur constantly(as often as one per genelocus
of
per lOs gametes).Mutationprovidesthe raw materialon which othermechanisms
for
evolutionary
directly
responsible
if
ever,
is
rarely,
Mutation
work.
microevolution
change.
D. Nonrandom mating is more often the case,particularly amonganimals,wherechoice of
mates is often an important part of behaviorbut doesnot changeallele frequencyand
therefore does not affect microevolution.
E. Differential successin reproductionis probablyalwaysthe casefor naturalpopulations.
The resulting natural selectionis the factor that is likely to result in adaptivechangesto
a genepool.
NOTE: Differential reproductivesuccessis measuredin terrnsof fitnessdifferences
(Module13.18).
Module 13.12 Adaptivechangeresultswhen naturalselectionupsetsgeneticequilibrium.
A. The amount and kind of geneticvariation in the populationlimit the degreeof adaptation that can occur.
III. Variation and Natural Selection
Module 13.13 Variationis extensivein most populations.
A. Variation in a single characteristiccan be causedby the effect of one or more genesor
from the action of the environmentinducing phenotypicchange.
B. A population is polymorphic for a characteristicif two or more morphs(contrasting
forms) are noticeablypresent;thesemay be visible or biochemicalcharacteristics
Chapter 13 How Populations Evolve
127
(Figure 13.13).Much of this variationcanbe attributedto polygenicinheritance.
Review:Polygenicinheritanceis discussed
in Module9.16.
C. Most populationsexhibit geographicvariationin the distributionof characreristics.
This
variationmay show stratificationor be clinal, varyingsmoothlyacrossthe population.
D. Geneticvariationcan be measuredin two ways:first, by determiningthe averagepercent of geneloci that are heterozygous
(genediversity);second,by determiningthe
nucleotidediversityof DNA sequences.
Module 13.14 Connection:Mutation and sexualrecombination
generatevariation.
A. Review:Mutation(Module 10.16)andmeiosis(especially
Modules8.16,8.17,
and8.18).
NOTE: Mutationis the ultimatesourceof all variation.
B. Mutationsnormally are harmful,but theymay improvean organism'sadaptationto an
environmentthat is changing.Organismswith very shortgenerationspans,like bacteria,
can evolverapidly by mutationalone.
C. Sexualrecombinationshufflesthe mixtureof allelesin diploid organisms.Independent
assortment,crossingover, and randomfertilization of spermand egg all play a role.
Organismsthat reproducesexuallytendto havelongerlife spans,and sexualrecombination is necessaryto increasethe variationstemmingfrom single mutations (Figure
13.14).
Module 13.15 Overview:How naturalselectionaffectsvariation.
A. An ancestralpopulationis varied,with individualshavingcharacteristics
suitedfor
many types of environments.
B. Over successive
generations,
thoseindividualswith the characteristics
best suitedfor
the environmentleavemore offspring.Thesecharacteristics
increasein the subsequent
generations.
C. Those individuals with characteristicsnot suitedfor the environmentleave fewer offspring.Thesecharacteristics
decrease
in subsequent
generations.
D. The effectsof recessiveallelesare not oftendisplayedin diploid organisms.Recessive
alleles may be "hidden" from natural selectionwhen they are found in combination
with a dominantallele.Thus,variationis retainedin a populationsubjectto selection.
NOTE: Since suchvariation is hidden it takesmany generationsto eliminate (if they are
eliminatedat all) disadvantageous
recessive
allelesfrom a population.
Review:Cystic fibrosisis only expressed
in individualswho are homozygousrecessive
for this disorder(Module 9.9).
E. Heterozygote advantage is a situationin which the heterozygoteis favored over either
homozygote.As a result,variationis maintainedin the population.An exampleof this
is the sickle-cellallele whereone homozygote
is susceptible
to malaria,the other
homozygotesuffersfrom sickle-celldisease,
and the heterozygote
is resistantto malaria
and normally doesnot sufferfrom sickle-celldisease(Module9.14).
F. A secondmechanismthat promotesbalancedpolymorphismis frequency-dependent
selection.For example,if too many of onetype (or morph)of organismis presentin a
population,that type will be selectedagainst,reducingttrattype'stotal numbers.
Module 13.16 Not all geneticvariationmay be subjectto naturalselection.
A. Somecharacteristics
showingneutral variation (suchas humanfingerprints)apparently
provideno selectiveadvantage(Figure13.16).
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Instructor's Guide to Tbxt and Media
may changeas a result of geneticdrift, but not
B. The frequencyof thesecharacteristics
by naturalselection.
that an allele brings no benefit to an organism,and it
C. It is impossibleto demonstrate
maybe that somesupposedlyneutralvariationsprovide benefitsin someenvironments.
Module 13.17Connection:Endangeredspeciesoften havereducedvariation.
A. This is becomingmore and more of a problemas human activity (habitatdestruction,
the introductionof exotic lnonnative]species,unregulatedhunting) endangerswild populations,particularlythosethat are small to begin with.
of suchhumanactivity are discussedin Chapter38.
NOTE:The consequences
B. Thereis about0.04Voheterozygosityin the geneloci of the SouthAfrican populationof
the cheetah,and l.4Voheterozygosityin the EastAfrican population.Theseanimals
sufferedbottlenecksdue to disease,hunting, and drought.
NOTE:This is an extremelyhigh degreeof genetic uniformity-higher than some
strainsof highly inbred laboratorymice.
exhibitedby cheetahs,coupledwith loss of habitat,
C. The high degreeof heterozygosity
in
the
wild
opento question.
leavesthe cheetah'sfuture
NOTE:Ask your studentsif cheetatrsshould be preservedby human intervention.
Sooneror later speciesgo extinct;perhapsit is the preservation,not the extinction,of
the cheetatrthat will be due to human interference.
Module 13.18The perpetuationof genesdefinesevolutionaryfitness.
A. Emphasizethat it is the survival of genesand the phenotypic traits expressedby the
genes,not individual organisms,that are important. It is the genesthat survive through
the passageof time, not the individualorganism(s),that are important.
B. Darwinian fitness is definedas the relative contribution that an individual makesto the
genepool of the next generation.
Module 13.19Thereare threegeneraloutcomesof naturalselection(Figure 13.19).
A. Stabilizing selectiontendsto n:urow the range in population variability toward some
intennediateform. This occursin relatively stableenvironments.
Preview:An exampleof stabilizing selectionis the birth weight of humanbabies,which
tendsto be in the 6.5-9-poundrange(Module 27.17).
B. Directional selectiontendsto move the modal (most common) form toward one of the
exftemes.This is most commonduring times of environmentalchange,or when organin new habitats.
ismsfind themselves
Preview:A good exampleof the effects of directional selection on life history patterns
canbe found in the discussionof guppies subjectto different selectivepressures
(Module35.7).
C. Diversifying selectionoccurswhen environmentalconditions are varied in a way that
favorsboth extremesover t}te intermediateform.
Module L3.20 Sexualselectionmay producesexualdimorphism.
A. Sexualdimorphism is illustratedby two examplesof secondarysexualcharacteristics.
B. Competitionbetweenmalesfor the privilege to mate with a female may dependon the
strengthof the male and his superiorability comparedto other males (Figure 13.20A).
Chapter 13 How Populations Evolve
129
suchas plumagein birds may actuallybe detrimentalto the surC. Othercharacteristics
due
to increasedrisk of predators.The rewardof mateselectiondue
vival of the male
to a largerplumagethan other males,however,may outweighthe potentialrisk factors
(Figure13.208).
Module 13.21 Naturalselectioncannotfashionperfectorganisms.
A. There are four reasonsthat accountfor imperfections in organismsin spite of natural
selection:
1. Organismsare lockedinto historicalconstraints;naturedoesn'tstartfrom scratch
eachtime thereis a needfor change.
2. Adaptationsare often compromises;someadaptationsto changeprovidean advantagealongwith a disadvantage.
3. Not all evolutionis adaptive;nature'sways are not alwaysin the bestinterestof the
organismin question.
4. Selectioncan only edit existingvariations;if an adaptationto changeis neededand
noneis availablein a population,that population may becomeextinct.
B. Natural selectionoperateson a "better than" basis and it would be unreasonableto
expectperfectionfrom a processwith suchlimitations.
Module 13.22 Connection:The evolutionof antibioticresistancein bacteriais a seriouspublic
healthconcern.
A. Antibiotics were first developedin the 1930sand becamestandardmedicalpracticefor
the preventionof infectious diseasesduring WWII.
B. Forcesof evolution (natural selection)have acceleratedthe developmentof antibioticresistantstrainsof bacteria.
Review:Antibiotic resistanceis caried on plasmids that are easily transferredbetween
bacterialcells (Module 12.2).
C. Overuseand misuseof antibiotics has contributed to the proliferation of antibioticresistantsftains of bacteria.
D. Multidrug-resistantstrainsof the organismthat causestuberculosis(Mycobacterium
tuberculosis)have appearedat alarming rates in the United Statesand are ravaging
other parts of the world (Figure 13.22).
ClassActivities
l.
equationplays a role in public healthscience.
As pointedout in Module 13.9,theHardy-Weinberg
by having students,working in groups,choosea healthissuethat hasa
This rolecanbe demonstrated
geneticbasis(e.g.,PKU, cysticfibrosis,sickle-celldisease,Tay-Sachs,etc.)and seehow it appliesto
public healthplanningin the communityin which they live. The currentandprojectedpopulationsize
whencompletingthis exercise.
of thecommunitymustbe considered
2.
Point outthat one of the major healthcarecriseshumansare facing is the developmentof antibioticresistantbacteria.Ask your studentshow many of them,when given prescriptionantibiotics,finish the
entireprescription.Therewill, almostinevitably,be at leastone studentwho doesnot. Point out how
this contributesto the increasein the numbersof antibiotic-resistantstrainsof bacteria.Further,as discussedin Chapterl2,bacteia canexchangeplasmids;thus,bacterianeverexposedto a particular
antibioticcanbe resistantto that antibioticas a resultof plasmidexchange.
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Instructor's Guide to Tbxt and Media
Acetates
Transparency
Figure13.18
Figure 13.2H
Figure13.3A
Figure13.38
Figure 13.48
Figure I3.4C
Figure13.58
Figure13.8A
Figure13.88
Figure13.8C
Figure13.11A
Figure13.14
Figure13.19
Figure13.19
Figure13.19
Theinsetsshowa youngCharlesDarwinand
The voyageof theBeagle(1831-1836).
his ship.
Basilosauru.r,an extinctwhalewhosehind legslink living whaleswith their landdwelling ancestors
Homologousstructures:vertebrateforelimbs
basedon hemoEvolutionaryrelationshipsbetweenhumansandfive othervertebrates,
globin comparisons
theresultsof hundredsto thouFive breedsof dogs(all membersof the samespecies),
sandsof yearsof artificial selection
to millionsof yearsof natural
Five different speciesof canines,theresultsof thousands
selection
in insectpopulations
Evolution of insecticideresistance
Imaginaryblue-footedboobies,with andwithoutfoot webbing
Genepool of originalpopulationof boobies
Genepool ofnext generationofboobies
The bottleneckeffect
Shuffiing allelesby sexualrecombination
Threepossibleeffectsofnatural selectionon a phenotypiccharacter(Layer l)
Threepossibleeffectsof naturalselectionon a phenotypiccharacter(Layet 2)
Threepossibleeffectsof naturalselectionon a phenotypiccharacter(Layer3)
Media
Seethe beginning of this book for a completedescriptionof all media availablefor instructorsand students.Animations and videos are availablein the CampbellImagePresentationLibrary. Media Activities
andThinking as a Scientist investigationsare availableon the studentCD-ROM and web site.
AnimationsandVideos
FileName
TortoiseVideo
Dome-Backed
TortoiseVideo
Dome-Backed
IslandsOverviewVideo
Galdpagos
IslandsOverviewVideo
Galdpagos
MarineIguanaVideo
MarineIguanaVideo
GaldpagosSeaLion Video
GaldpagosSeaLion Video
GrandCanyonVideo
GrandCanyonVideo
13-01A-TortoiseVideo-B.mov
13-01A-TortoiseVideo-S.mov
13-01B-GalapagosVideo-B.mov
13-0lB-GalapagosVideo-S.mov
l3-018-MarinelguanaVideo-B.mov
l3-0lB-MarinelguanaVideo-S.mov
13-0lB-SealionVideo-B.mov
l3-0lB-SealionVideo-S.mov
13-02G-GrandCanyonVideo-B.mov
13-02G-GrandCanyonVideo-S.mov
Chapter13 How Populations Evolve
Activitiesand Thinkingasa Scientist
ModuleNumber
Web/CD Activity l3A: Darwin and the GaldpagosIslands
Web/CD Activity I3B: The Voyageof the Beagle: Danvin's Trip
Around the World
13.1
Web/CD Activity I3C: ReconstructingForelimbs
Web/CD Thinking as a Scientist: How Do Environmental
ChnngesAffect a Population?
Biology Labs On-Line: EvolutionLab
Web/CD Thinking as a Scientist: How Can Frequency of Alleles
Be Calculated?
Web/CD Activity \3D: Causesof Microevolution
Biology Labs On-Line: PopulationGeneticsLab
Web/CD Activity l3Fl. Genetic Variation from Sexual
Recombination
Web/CD Thinking as a Scientist: Connection: What Are the
Pattents of Antibiotic Resistance?
13.1
13.3
t3.4
13.5
13.8
13.11
13.11
13.r4
13.22
131