This document provides an overview of Chapter 15 on evolution from a biology textbook. Section 15.1 discusses Charles Darwin's theory of natural selection, which proposes that evolution occurs through natural selection acting on random genetic variations in populations over multiple generations. The four main principles of natural selection are described. Section 15.2 reviews various lines of evidence that support the theory of evolution, including the fossil record, comparative anatomy, embryology, biochemistry and geographic distribution of species. Section 15.3 discusses how evolutionary theory has been refined over time, including ideas around genetic drift, speciation factors, gradualism versus punctuated equilibrium, and sexual selection.

1. Chapter 15Chapter 15
EvolutionEvolution
15.1 Darwin15.1 Darwin’s Theory of Natural Selection’s Theory of Natural Selection
15.2 Evidence of Evolution15.2 Evidence of Evolution
15.3 Shaping Evolutionary Theory15.3 Shaping Evolutionary Theory

2. 15.1 Darwin15.1 Darwin’s Theory of Natural Selection’s Theory of Natural Selection
Main idea:Main idea: Charles Darwin developed a theory ofCharles Darwin developed a theory of
evolution based on natural selectionevolution based on natural selection
ObjectivesObjectives

Discuss the evidence that convinced DarwinDiscuss the evidence that convinced Darwin
that species could change over time.that species could change over time.

List the four principles of natural selection.List the four principles of natural selection.

Show how natural selection could change aShow how natural selection could change a
populationpopulation
New VocabularyNew Vocabulary

Selective breeding, Artificial selection, NaturalSelective breeding, Artificial selection, Natural
selection, Evolutionselection, Evolution

3. Charles DarwinCharles Darwin boardedboarded
the HMS Beaglethe HMS Beagle inin 18311831..
Most believed the worldMost believed the world
was aboutwas about 6,0006,000 years old.years old.
During the shipDuring the ship’s five year’s five year
voyage, Darwin madevoyage, Darwin made
extensive collections ofextensive collections of
rocks,rocks, fossilsfossils, plants and, plants and
animals.animals.
He also read Charles LyellHe also read Charles Lyell’s’s Principles ofPrinciples of
GeologyGeology – a book proposing the Earth– a book proposing the Earth
waswas millionsmillions of years old.of years old.
Developing the Theory ofDeveloping the Theory of
Natural SelectionNatural Selection

4. In 1835, the Beagle arrived in theIn 1835, the Beagle arrived in the
Galapagos Islands off the coast of SouthGalapagos Islands off the coast of South
America.America.
Darwin began to collect mockingbirds,Darwin began to collect mockingbirds,
finches, and other animals on thefinches, and other animals on the fourfour
islands.islands.
He noticed that theHe noticed that the differentdifferent islandsislands
seemed to have their own, slightlyseemed to have their own, slightly
differentdifferent varietiesvarieties of animals.of animals.
Developing the Theory ofDeveloping the Theory of
Natural SelectionNatural Selection
HMS BeagleHMS Beagle

5. Almost everyAlmost every
specimenspecimen
that Darwinthat Darwin
had collectedhad collected
on the islandson the islands
was new towas new to
EuropeanEuropean
scientists.scientists.
Darwin suspected populations from the mainlandDarwin suspected populations from the mainland
changedchanged after reaching the Galápagos.after reaching the Galápagos.
Galápagos IslandsGalápagos Islands
Developing the Theory ofDeveloping the Theory of
Natural SelectionNatural Selection

6. Darwin hypothesized thatDarwin hypothesized that newnew speciesspecies
could appearcould appear graduallygradually through smallthrough small
changeschanges in ancestral species.in ancestral species.
Darwin inferred that if humans couldDarwin inferred that if humans could
change species bychange species by artificial selectionartificial selection
(selective breeding), then perhaps the(selective breeding), then perhaps the
same process could work insame process could work in naturenature..
Developing the Theory ofDeveloping the Theory of
Natural SelectionNatural Selection

7. Darwin called his theoryDarwin called his theory Natural SelectionNatural Selection
Developing the Theory ofDeveloping the Theory of
Natural SelectionNatural Selection
Natural SelectionNatural Selection
He reasoned that,He reasoned that,
given enough time,given enough time,
natural selection couldnatural selection could
modifymodify a populationa population
enough to produce aenough to produce a
new species.new species.

8. Basic Principles of Natural SelectionBasic Principles of Natural Selection

9. Darwin publishedDarwin published On the Origin of SpeciesOn the Origin of Species
by Means of Natural Selectionby Means of Natural Selection in 1859.in 1859.
Today, biologists use the term evolution toToday, biologists use the term evolution to
definedefine changeschanges in groups of organismsin groups of organisms
throughthrough time.time.
DarwinDarwin’s theory of natural selection is’s theory of natural selection is
NOTNOT the same as evolution. Naturalthe same as evolution. Natural
selection is a means of explainingselection is a means of explaining HOWHOW
evolutionevolution works.works.
The Origin of SpeciesThe Origin of Species

10. 15.2 Evidence of Evolution15.2 Evidence of Evolution
Main idea:Main idea: Multiple lines of evidence support theMultiple lines of evidence support the
theory of evolution.theory of evolution.
Objectives:Objectives:

Describe how fossils provide evidence ofDescribe how fossils provide evidence of
evolution.evolution.

Discuss morphological evidence of evolution.Discuss morphological evidence of evolution.

Explain how physiology and biochemistryExplain how physiology and biochemistry
provide evidence of evolution.provide evidence of evolution.
New VocabularyNew Vocabulary

Derived traitDerived trait

Ancestral traitAncestral trait

Homologous structureHomologous structure

Vestigial structureVestigial structure

Analogous structureAnalogous structure

EmbryoEmbryo

FitnessFitness

MimicryMimicry

CamouflageCamouflage

11. Support for EvolutionSupport for Evolution
The theory ofThe theory of evolutionevolution states that allstates that all
organisms on Earth have descended from aorganisms on Earth have descended from a
common ancestorcommon ancestor..
TheThe fossil recordfossil record offers some of the mostoffers some of the most
significant evidence of evolutionary change.significant evidence of evolutionary change.

Fossils provide aFossils provide a recordrecord of species thatof species that
lived long ago.lived long ago.

Fossils show that ancient species shareFossils show that ancient species share
similaritiessimilarities with species that now live onwith species that now live on
Earth.Earth.

12. The giant armadillo-likeThe giant armadillo-like
glyptodont,glyptodont, Glyptodon,Glyptodon,isis
anan extinctextinct animal thatanimal that
Darwin thought must beDarwin thought must be
related to therelated to the livingliving
armadillos of today.armadillos of today.
TheThe fossil recordfossil record providesprovides
information forinformation for
determining the ancestrydetermining the ancestry
of organisms and theof organisms and the
patternspatterns of evolution.of evolution.
Support for EvolutionSupport for Evolution
The Fossil RecordThe Fossil Record

13. Two major classes of traits:Two major classes of traits:
Derived traits areDerived traits are newly evolvednewly evolved
features, such as feathers, that do notfeatures, such as feathers, that do not
appear in the fossils of commonappear in the fossils of common
ancestors.ancestors.
Ancestral traitsAncestral traits are moreare more primitiveprimitive
featuresfeatures, such as teeth and tails, that, such as teeth and tails, that
do appear in ancestral forms.do appear in ancestral forms.
Support for EvolutionSupport for Evolution
The Fossil RecordThe Fossil Record

14. Transitional fossils provide detailedTransitional fossils provide detailed
patternspatterns of evolutionary change forof evolutionary change for
ancestors of many modern animals,ancestors of many modern animals,
including mollusks, horses, whales andincluding mollusks, horses, whales and
humans.humans.
Example:Example:

ArcheopteryxArcheopteryx
Shares features ofShares features of
bothboth dinosaursdinosaurs
and birds.and birds.
Support for EvolutionSupport for Evolution
The Fossil RecordThe Fossil Record

15. HomologousHomologous
structures arestructures are
anatomicallyanatomically
similarsimilar structuresstructures
inheritedinherited from afrom a
commoncommon
ancestor.ancestor.
The forelimbs ofThe forelimbs of
vertebrates arevertebrates are
adapted foradapted for
different uses,different uses,
but they all havebut they all have
similar bones.similar bones.
SimilarSimilar structure;structure; differentdifferent
functionfunction..
Support for EvolutionSupport for Evolution
Comparative AnatomyComparative Anatomy

16. Vestigial structures areVestigial structures are
thethe reducedreduced forms offorms of
functional structures infunctional structures in
other organisms.other organisms.
Evolutionary theoryEvolutionary theory
predicts that featurespredicts that features
of ancestors that noof ancestors that no
longer have a functionlonger have a function
for that species willfor that species will
becomebecome smallersmaller overover
time until they aretime until they are lostlost..
Examples: Snake pelvis,Examples: Snake pelvis,
humanhuman appendix,appendix, blindblind
fish and salamanders thatfish and salamanders that
live in caves but havelive in caves but have
eyes.eyes.
Support for EvolutionSupport for Evolution
Comparative AnatomyComparative Anatomy

17. Analogous structures can beAnalogous structures can be
used for theused for the same purposesame purpose
and can beand can be similarsimilar inin
construction, but areconstruction, but are notnot
inheritedinherited from a commonfrom a common
ancestor.ancestor.
Show that functionally similarShow that functionally similar
features can evolvefeatures can evolve
independentlyindependently in similarin similar
environments.environments.
DifferentDifferent structure;structure; samesame
function;function;
Support for EvolutionSupport for Evolution
Comparative AnatomyComparative Anatomy

18. Analogous structures example:Analogous structures example:

Human eye and squid eyeHuman eye and squid eye
SimilaritiesSimilarities

The iris to regulate light entering the lensThe iris to regulate light entering the lens

Each eye is filled with fluidEach eye is filled with fluid

Both eyes use a lens to focusBoth eyes use a lens to focus
function;function;
Support for EvolutionSupport for Evolution
Comparative AnatomyComparative Anatomy

19. AnAn embryoembryo is an early pre-birth stage of anis an early pre-birth stage of an
organismorganism’s development.’s development.
VertebrateVertebrate
embryos exhibitembryos exhibit
homologoushomologous
structuresstructures
during certainduring certain
phases ofphases of
developmentdevelopment
but becomebut become
totally differenttotally different
structures instructures in
the adult forms.the adult forms.
Support for EvolutionSupport for Evolution
Comparative EmbryologyComparative Embryology

20. Comparative BiochemistryComparative Biochemistry
Common ancestryCommon ancestry
can be seen in thecan be seen in the
complexcomplex metabolicmetabolic
moleculesmolecules thatthat
many differentmany different
organismsorganisms shareshare..
Support for EvolutionSupport for Evolution
The genomes of humans and chimpanzeesThe genomes of humans and chimpanzees
differ by only about 1% of their genetic makeupdiffer by only about 1% of their genetic makeup

21. Geographic DistributionGeographic Distribution
TheThe distributiondistribution of plants and animals thatof plants and animals that
Darwin saw during his travels firstDarwin saw during his travels first
suggested evolution to Darwin.suggested evolution to Darwin.
Rabbit in EuropeRabbit in Europe Mara in S. AmericaMara in S. America
Support for EvolutionSupport for Evolution

22. Scientists haveScientists have
confirmed andconfirmed and
expanded Darwinexpanded Darwin’s’s
study of the distributionstudy of the distribution
of plants and animalsof plants and animals
around the world in aaround the world in a
field of study now calledfield of study now called
biogeography.biogeography.
Evolution is intimately linked withEvolution is intimately linked with
climateclimate andand geologicalgeological forcesforces..
Geographic DistributionGeographic Distribution
Support for EvolutionSupport for Evolution

23. AdaptationAdaptation
AnAn adaptationadaptation is a traitis a trait
shaped by naturalshaped by natural
selection thatselection that increasesincreases
an organisman organism’s’s
reproductive success.reproductive success.
FitnessFitness is a measure of the relativeis a measure of the relative
contribution an individual trait makes to thecontribution an individual trait makes to the
next generation. It is often measured as thenext generation. It is often measured as the
number ofnumber of reproductivelyreproductively viable offspring thatviable offspring that
an organism produces in the next generation.an organism produces in the next generation.

24. Camouflage allowsCamouflage allows
organisms to becomeorganisms to become
almostalmost invisibleinvisible toto
predators. Some speciespredators. Some species
have evolved morphologicalhave evolved morphological
adaptations that allow themadaptations that allow them
to blend in with theirto blend in with their
environments.environments.
MimicryMimicry is anotheris another
morphological adaptationmorphological adaptation
that allows one species tothat allows one species to
evolve toevolve to resembleresemble
another speciesanother species..
AdaptationAdaptation
Types of AdaptationTypes of Adaptation

25. Can you see the peppered moth?Can you see the peppered moth?
AdaptationAdaptation
Types of AdaptationTypes of Adaptation

26. When disturbed,When disturbed,
this octopus flashesthis octopus flashes
and intensifies itsand intensifies its
stripes, resemblingstripes, resembling
a poisonous seaa poisonous sea
snake. Unlike thesnake. Unlike the
sea snake, thesea snake, the
octopus venom isoctopus venom is
harmlessharmless
AdaptationAdaptation
Types of AdaptationTypes of Adaptation

27. AntimicrobialAntimicrobial
resistanceresistance - An- An
antibiotic is aantibiotic is a
medicine that slowsmedicine that slows
or kills the growth ofor kills the growth of
bacteria.bacteria.

Some bacteriaSome bacteria
have evolved ahave evolved a
resistanceresistance toto
certain antibiotics.certain antibiotics.

People infected with resistant bacteria canPeople infected with resistant bacteria can nevernever get rid ofget rid of
it.it.
AdaptationAdaptation
Types of AdaptationTypes of Adaptation

28. 15.3 Shaping Evolutionary Theory15.3 Shaping Evolutionary Theory
Main idea:Main idea: The theory of evolution continues toThe theory of evolution continues to
be refined as scientists learn new information.be refined as scientists learn new information.
Objectives:Objectives:

Discuss patterns observed in evolution.Discuss patterns observed in evolution.

Describe factors that influence speciation.Describe factors that influence speciation.

Compare gradualism with punctuated equilibrium.Compare gradualism with punctuated equilibrium.
Review VocabularyReview Vocabulary

Allele: alternative forms of a character trait that canAllele: alternative forms of a character trait that can
be inherited.be inherited.

29. 15.3 Shaping Evolutionary Theory15.3 Shaping Evolutionary Theory
Hardy-Weinberg PrincipleHardy-Weinberg Principle
Genetic driftGenetic drift
Founder effectFounder effect
BottleneckBottleneck
Punctuated EquilibriumPunctuated Equilibrium
Sexual selectionSexual selection
New Vocabulary

30. Mechanisms of EvolutionMechanisms of Evolution
Darwin’s theory of natural selectionDarwin’s theory of natural selection
remainsremains the central theme ofthe central theme of
evolutionevolution
Scientists of today know that naturalScientists of today know that natural
selection is not the only mechanismselection is not the only mechanism
of evolutionof evolution
Evolution occurs at theEvolution occurs at the populationpopulation
level, with genes as thelevel, with genes as the raw material.raw material.

31. Mechanisms of EvolutionMechanisms of Evolution
Hardy-Weinberg Principle states that whenHardy-Weinberg Principle states that when
allelic frequencies remain constant, a populationallelic frequencies remain constant, a population
is in geneticis in genetic equilibriumequilibrium..
Population GeneticsPopulation Genetics

Even though the number of owls doubled, theEven though the number of owls doubled, the ratioratio ofof
gray to red owls remained thegray to red owls remained the same.same.

32. pp22
+ 2pq + q+ 2pq + q22
= 1= 1
This equation allows us to determine theThis equation allows us to determine the
equilibriumequilibrium frequency of eachfrequency of each genotypegenotype inin
the population:the population:
homozygoushomozygous dominant (pdominant (p22
))
heterozygousheterozygous (2pq)(2pq)
homozygoushomozygous recessive (qrecessive (q22
))
Note the sum of these frequencies equalsNote the sum of these frequencies equals one.one.
Mechanisms of EvolutionMechanisms of Evolution
Population GeneticsPopulation Genetics

33. A population in genetic equilibrium must meet allA population in genetic equilibrium must meet all
fivefive conditionsconditions
1.1.The population is veryThe population is very largelarge
2.2.NoNo immigrationimmigration oror emigrationemigration
3.3.Mating isMating is randomrandom
4.4.MutationsMutations do not occur (no new variations)do not occur (no new variations)
5.5.Natural selectionNatural selection does not occurdoes not occur
Population GeneticsPopulation Genetics
Mechanisms of EvolutionMechanisms of Evolution

34. Genetic Drift is a change in the allelicGenetic Drift is a change in the allelic
frequencies in a population that is due tofrequencies in a population that is due to
chancechance..
InIn smallersmaller populations, the effects ofpopulations, the effects of
genetic drift becomes moregenetic drift becomes more pronouncedpronounced,,
and the chance of losing an alleleand the chance of losing an allele
becomes greater.becomes greater.
Examples: Founder Effect & BottleneckExamples: Founder Effect & Bottleneck
Mechanisms of EvolutionMechanisms of Evolution
Genetic DriftGenetic Drift

35. Founder EffectFounder Effect occurs when a smalloccurs when a small
sample of a population settles in a locationsample of a population settles in a location
separatedseparated from the rest of thefrom the rest of the populationpopulation
Genetic DriftGenetic Drift
Alleles that wereAlleles that were
uncommonuncommon in thein the
original populationoriginal population
might bemight be commoncommon
in the newin the new
population.population.
Mechanisms of EvolutionMechanisms of Evolution

36. Bottleneck occursBottleneck occurs
when a populationwhen a population
declinesdeclines to a veryto a very
low number andlow number and
thenthen reboundsrebounds
Mechanisms of EvolutionMechanisms of Evolution
Genetic DriftGenetic Drift

CanCan decreasedecrease
geneticgenetic variety.variety.

37. A population in genetic equilibriumA population in genetic equilibrium
experiences noexperiences no gene flowgene flow,, however, fewhowever, few
populations arepopulations are isolatedisolated
RandomRandom movement of individuals betweenmovement of individuals between
populationspopulations reducesreduces differences betweendifferences between
populationspopulations
Mechanisms of EvolutionMechanisms of Evolution
Gene FlowGene Flow

38. RarelyRarely is matingis mating
completely random in acompletely random in a
population.population.
Usually individuals mateUsually individuals mate
with individuals in closewith individuals in close
proximityproximity..
Nonrandom matingNonrandom mating
Mechanisms of EvolutionMechanisms of Evolution
This promotes inbreeding and could lead to aThis promotes inbreeding and could lead to a
change in allelic proportions favoring individualschange in allelic proportions favoring individuals
that arethat are homozygoushomozygous for particular traits.for particular traits.

39. A mutation is aA mutation is a randomrandom
changechange in geneticin genetic
material.material.
Occasionally mutationsOccasionally mutations
provide anprovide an advantageadvantage toto
organisms and becomeorganisms and become
more common inmore common in
subsequent generations.subsequent generations.
Basis upon whichBasis upon which naturalnatural
selectionselection works.works.
Mechanisms of EvolutionMechanisms of Evolution
MutationMutation

40. Select the individuals that areSelect the individuals that are
best adapted forbest adapted for survivalsurvival andand
reproductionreproduction
StabilizingStabilizing selectionselection

eliminate extremeeliminate extreme
expressionsexpressions
Birth WeightsBirth Weights
DirectionalDirectional selectionselection

makes organisms more fit.makes organisms more fit.
Peppered MothsPeppered Moths
DisruptiveDisruptive selectionselection

process that splits aprocess that splits a
population into two groups.population into two groups.
Lake Erie WaterLake Erie Water
SnakesSnakes
Mechanisms of EvolutionMechanisms of Evolution
Natural SelectionNatural Selection

41. Sexual selectionSexual selection operates inoperates in
populations where males andpopulations where males and
females differ significantly infemales differ significantly in
appearanceappearance..

MalesMales are largest and mostare largest and most
colorful in the groupcolorful in the group

More likely target forMore likely target for predatorspredators
yet bodies enhance reproductiveyet bodies enhance reproductive
successsuccess
Examples: Peacocks & DeerExamples: Peacocks & Deer
Natural SelectionNatural Selection
Mechanisms of EvolutionMechanisms of Evolution

42. preventsprevents reproductionreproduction
by making fertilizationby making fertilization
unlikely.unlikely.

Eastern and WesternEastern and Western
meadowlarks similarmeadowlarks similar
in appearance butin appearance but
their mating songstheir mating songs
separate themseparate them
behaviorally.behaviorally.
Reproductive IsolationReproductive Isolation
Prezygotic IsolationPrezygotic Isolation

43. Occurs whenOccurs when
fertilization hasfertilization has
occurredoccurred but abut a
hybrid offspringhybrid offspring
cannot developcannot develop
or reproduce.or reproduce.
Reproductive IsolationReproductive Isolation
Postzygotic IsolationPostzygotic Isolation

A Liger is the offspring of a male lionA Liger is the offspring of a male lion
and a female tiger. Ligers areand a female tiger. Ligers are sterile.sterile.

44. AA physicalphysical barrier divides one populationbarrier divides one population
into two or more populations.into two or more populations.
SpeciationSpeciation
Allopatric speciationAllopatric speciation
For speciation to occur, a population mustFor speciation to occur, a population must
divergediverge and then be reproductivelyand then be reproductively isolatedisolated..

45. Species evolves into a new speciesSpecies evolves into a new species
withoutwithout a physical barriera physical barrier
SpeciationSpeciation
Sympatric speciationSympatric speciation

Apple maggot fliesApple maggot flies
lay eggs on apples orlay eggs on apples or
hawthorns dependinghawthorns depending
on the type of fruiton the type of fruit
the grew up on.the grew up on.
For speciation to occur, a population mustFor speciation to occur, a population must
diverge and then be reproductively isolated.diverge and then be reproductively isolated.

46. Can occur in a relativelyCan occur in a relatively shortshort time when onetime when one
species gives rise tospecies gives rise to manymany different speciesdifferent species
in response to the creation of newin response to the creation of new habitathabitat oror
some other ecological opportunity.some other ecological opportunity.
Patterns of EvolutionPatterns of Evolution
Adaptive Radiation (aka divergent evolution)Adaptive Radiation (aka divergent evolution)
FollowsFollows
large-scalelarge-scale
extinctionextinction
eventsevents

Cichlid fishCichlid fish
of Lakeof Lake
Victoria inVictoria in
Africa.Africa.

47. The relationship between two species might beThe relationship between two species might be
so close that the evolution of one speciesso close that the evolution of one species affectsaffects
the evolutionthe evolution of the other species.of the other species.
MutualismMutualism – occurs when two species benefit– occurs when two species benefit
each other.each other.
CoevolutionCoevolution
Patterns of EvolutionPatterns of Evolution

48. The plant evolves aThe plant evolves a
chemical defensechemical defense
The insects evolve theThe insects evolve the
biochemistry tobiochemistry to resistresist thethe
defensedefense
 Response continues to escalate.Response continues to escalate.
Patterns of EvolutionPatterns of Evolution
CoevolutionCoevolution
Coevolutionary arms race – one species canCoevolutionary arms race – one species can
evolve a parasiticevolve a parasitic dependencydependency on anotheron another
species.species.
A plant and an insect that is dependent onA plant and an insect that is dependent on
the plant for foodthe plant for food

49. UnrelatedUnrelated speciesspecies
evolve similar traitsevolve similar traits
even though they liveeven though they live
inin differentdifferent parts ofparts of
the world.the world.
Occurs inOccurs in
environments that areenvironments that are
geographically fargeographically far
apart but have similarapart but have similar
ecologyecology andand climate.climate.
Patterns of EvolutionPatterns of Evolution
Convergent EvolutionConvergent Evolution

50. PunctuatedPunctuated
equilibriumequilibrium
explainsexplains rapidrapid
spurts of geneticspurts of genetic
change causingchange causing
species tospecies to
divergediverge quicklyquickly..
Rate of SpeciationRate of Speciation
Patterns of EvolutionPatterns of Evolution
Evolution proceeds inEvolution proceeds in smallsmall,, gradualgradual steps =steps =
gradualism.gradualism.