Descent with Descent with Modification: Modification:

A Darwinian A Darwinian View of LifeView of Life

BIOL BIOL 102: 102: General Biology IIGeneral Biology II

Chapter Chapter 2222

Rob Rob SwatskiSwatski Associate Professor Associate Professor of Biologyof Biology

HACCHACC--YorkYork

2

1859: Charles Darwin 1859: Charles Darwin published published

The The Origin Origin of Species of Species

3

Main Ideas Main Ideas of Evolutionof Evolution

Current species are descendants

of ancestral species

“Descent with modification”

Natural selection

DescendantsDescendants

AncestorAncestor 4

5

Evolution accounts Evolution accounts for the unity & for the unity & diversity of lifediversity of life

Theodosius Theodosius DobzhanskyDobzhansky

“Nothing in biology makes sense

except in the light of evolution.”

6

7

8

1809

1798

1812

1795

1830

1790 1809 183136

1844

1859 1870

Lamarck publishes his hypothesis of evolution.

Malthus publishes “Essay on the Principle

of Population.”

Hutton proposes his principle of

gradualism.

Charles Darwin

is born.

Darwin travels around the world on HMS

Beagle.

The Galápagos Islands

Darwin writes his essay on descent with modification.

On the Origin of Species is published.

While studying species in

the Malay Archipelago,

Wallace (shown in 1848)

sends Darwin his hypothesis

of natural selection.

1858 Cuvier publishes his extensive studies of vertebrate fossils.

Lyell publishes

Principles of Geology.

Ancient ViewsAncient Views

Aristotle

Species are fixed & arranged on a scala

naturae

Old Testament

Species were individually designed

by God and, therefore, perfect

9

ScalaScala NaturaeNaturae God in

Heaven

Angels

Humans

Animals

Plants

Rocks

Devil in Hell 10

TaxonomyTaxonomy

Branch of biology that classifies organisms

into taxa

1700’s: Carl Linne, the “father of modern

taxonomy”

Viewed adaptations as evidence that the

Creator had designed each species for a specific purpose

11

12

Carl Carl LinneLinne “You can call me

Carolus Linnaeus”

13

14

Species Genus Family Order Class Phylum Kingdom Domain Ursus americanus (American black bear) Ursus

Ursidae

Carnivora

Mammalia

Chordata

Animalia

Eukarya

15 TaxonomyTaxonomy

FossilsFossils

Remains or traces of organisms from

the past

Usually found in sedimentary rock

layers (strata)

Established the groundwork for Darwin’s ideas

16

Younger stratum with more recent fossils

Layers of deposited sediment

Older stratum with older fossils

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18

19

20

21

SuedbergSuedberg Fossil PitFossil Pit Devonian 375 MYADevonian 375 MYA 22

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24

Geological Geological ViewsViews

Catastrophism Uniformitarianism

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CatastrophismCatastrophism

26

Charles LyellCharles Lyell

Principles of GeologyPrinciples of Geology 27

“The mechanisms of

“The mechanisms of

change are constant over

time”

UniformitarianismUniformitarianism

28

“The state of the natural world is the result “The state of the natural world is the result of a long succession of events.”of a long succession of events.” -- Charles LyellCharles Lyell

29

JeanJean--BaptisteBaptiste LamarckLamarck

Species evolve through the use & disuse of body

parts

Characteristics acquired during life are inherited

Unsupported by evidence

30

Lamarck’s HypothesisLamarck’s Hypothesis

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32

Aren’t you glad Aren’t you glad Lamarck Lamarck was wrong?was wrong? 33

Darwin’s Darwin’s ResearchResearch

Darwin always had a deep

interest in science & nature

Was a student of medicine & theology at Cambridge

5-year voyage on the Beagle after

graduation 34

Don’t Listen to Don’t Listen to Your ParentsYour Parents

“You care for

nothing but

shooting, dogs, and

rat-catching. You

will be a disgrace to

yourself and your

family.”

- DR. ROBERT DARWIN 35

Voyage of Voyage of the the BeagleBeagle

Collected specimens of South American plants &

animals

Observed adaptations to many diverse environments

Became interested in the geographic

distribution of species after a stop

at the Galápagos Islands

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37

Darwin in 1840, after his return from the voyage

The Galápagos Islands

NORTH AMERICA

ATLANTIC OCEAN

PACIFIC OCEAN

PACIFIC OCEAN

Pinta

Marchena

Genovesa

Equator

Chile

Santiago Daphne Islands

Fernandina

Isabela Santa Cruz

Santa Fe San

Cristobal

Española Kilometers

0 20 40 Florenza

Pinzón

SOUTH AMERICA

AFRICA

EUROPE

Great Britain

HMS Beagle in port

Equator

PACIFIC OCEAN

Malay Archipelago

AUSTRALIA

Tasmania

New Zealand

Brazil

Argentina

Cape Horn

An

des M

tns.

Cape of Good Hope

38

The Galápagos Islands

PACIFIC OCEAN Pinta

Marchena

Genovesa

Equator Santiago

Daphne Islands

Fernandina

Isabela Santa Cruz

Santa Fe San

Cristobal

Española Kilometers

0 20 40 Florenza

Pinzón

39

Darwin’s Darwin’s Focus on Focus on

AdaptationAdaptation

Adaptation to the environment & speciation are closely related

Strongly supported by

modern biology

Galápagos finches

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CactusCactus--eatereater

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InsectInsect--eatereater

42

SeedSeed--eatereater 43

Adaptive Radiation of Galápagos FinchesAdaptive Radiation of Galápagos Finches

44

If you had an idea thatIf you had an idea that was going to outragewas going to outrage

society…society…

would you keep would you keep it to yourself?it to yourself? 45

46

47

Darwin’s Two Main Ideas Darwin’s Two Main Ideas on Evolutionon Evolution

Descent with Descent with modification modification

Explains the unity &

diversity of life

Natural Natural SelectionSelection

Results in adaptive radiation

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Descent with Descent with ModificationModification

Darwin never used the word “evolution” in the 1st edition of Origin of

Species

“Descent with modification”

summarized his view of the unity of life

All organisms are related through descent from an ancestor that lived in the

distant past 49

50

The “Tree of The “Tree of Life”Life”

Branches represent life’s

diversity

Darwin’s theory meshed well with

Linnaeus’s hierarchy

Ex: elephants

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52

Hyracoidea

(Hyraxes)

Sirenia (Manatees and relatives)

†Deinotherium

†Mammut

†Platybelodon

†Stegodon

†Mammuthus

Elephas maximus

(Asia)

Loxodonta africana

(Africa)

Loxodonta cyclotis

(Africa)

†Moeritherium

†Barytherium

60

Millions of years ago

34 24 5.5 2 104 0

Years ago

53

Artificial Artificial SelectionSelection

Darwin noted that humans have

modified other species

Select & breed individuals with

desired traits

Selective breeding =

artificial selection 54

55

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57

Brussels

sprouts

Kale

Selection

for leaves

Selection for

axillary (side)

buds

Selection for

apical (tip) bud

Cabbage

Broccoli

Kohlrabi Wild mustard

Selection

for stems

Selection

for flowers

and stems

Four Four Observations Observations

of Nature of Nature Made by Made by DarwinDarwin

58

1.1. Members of a Members of a population often vary population often vary

greatly in their traitsgreatly in their traits 59

60

2.2. Traits are Traits are inheritedinherited from from parents to offspringparents to offspring 61

3.3. All species are All species are capable of producing capable of producing moremore offspring than offspring than the environment can the environment can supportsupport

62

4.4. Many offspring don’t surviveMany offspring don’t survive due to lack of food or predationdue to lack of food or predation 63

Two Inferences Two Inferences Made Made by Darwinby Darwin

64

1. Individuals whose inherited traits give them

a higher probability of surviving & reproducing in an environment tend to leave more offspring

than others

65

2. This unequal ability of individuals to survive & reproduce will lead to the accumulation of favorable traits in the

population over generations 66

Thomas Thomas MalthusMalthus

Another major influence on Darwin

Malthus wrote about the potential for

human population to increase faster than

food supplies & other resources

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68

Value of Value of Beneficial Beneficial

TraitsTraits

Traits that provide advantages will

accumulate in the population

This increases the frequency of

individuals having these adaptations

Explains the match between

organisms & their environment

69

Natural Natural SelectionSelection

Individuals with certain traits

survive & reproduce at a

higher rate than others

This increases the adaptation of

organisms to their environment over

time 70

71

72

Limits of Limits of Natural Natural

SelectionSelection

Can only increase or decrease heritable

traits in a population

Individuals do not evolve…

Populations evolve

73

Evolution is supported by Evolution is supported by an overwhelming amount an overwhelming amount of scientific evidenceof scientific evidence 74

Tiktaalik the fishapod! 75

76

Direct Observations of Direct Observations of Evolutionary ChangeEvolutionary Change

Natural selection in response to

introduced plant species

The evolution of drug-resistant

bacteria

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78

Soapberry bug with beak inserted in balloon vine fruit

FIELD STUDYFIELD STUDY Can a change in a Can a change in a population’s food population’s food source result in source result in evolution by evolution by natural selection?natural selection?

On native species,

southern Florida

Museum-specimen average

On introduced species,

central Florida

Nu

mb

er

of

ind

ivid

ua

ls

10

8

6

4

2

0

10

8

6

4

2

0

Beak

Beak length (mm)

6 7 8 10 11 9

79

RESULTSRESULTS

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1 2,750,000

2,500,000

2,250,000

2,000,000

1,750,000

1,500,000 1,250,000

1,000,000

750,000

500,000

250,000 base pairs

Chromosome map

of S. aureus clone USA300

Key to adaptations

Methicillin resistance

Ability to colonize hosts

Increased disease severity

Increased gene exchange

(within species) and

toxin production

MRSAMRSA

Mosquito Resistance to DDTMosquito Resistance to DDT

81

Summary of Summary of Natural Natural

SelectionSelection

It does not create new traits

It edits or selects for traits already present in

a population

The local environment determines which traits will be selected for or

against in a population 82

Fossils as Fossils as EvidenceEvidence

Species extinction

Origin of new taxonomic

groups

Changes within groups over time

83

Bristolia insolens

10

8

0

De

pth

(m

ete

rs)

4

Bristolia bristolensis

2

4

6

3

4

3

Latham Shale dig site, San Bernardino County, CA 84

Bristolia harringtoni

Bristolia mohavensis

12

14

16

18

2

De

pth

(m

ete

rs)

1

1

2

85

Transitional FormsTransitional Forms

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ArchaeopteryxArchaeopteryx 87

(a)(a) PakicetusPakicetus (terrestrial)(terrestrial)

(b)(b) RhodocetusRhodocetus (mostly aquatic(mostly aquatic))

The Transition The Transition to Life in the Seato Life in the Sea

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DorudonDorudon (fully aquatic)(fully aquatic) 89

(c)(c) DorudonDorudon (fully aquatic)(fully aquatic)

(d)(d) BalaenaBalaena (recent (recent whale ancestor)whale ancestor)

Pelvis and hind limb

Pelvis and hind limb

90

HomologyHomology

Similarity resulting from common

ancestry

Homologous structures

Similarities that represent variations

on a structural theme found in a common ancestor 91

Humerus

Radius

Ulna

Carpals

Metacarpals

Phalanges

HumanHuman WhaleWhale CatCat BatBat

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93

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Pharyngeal pouches

Post-anal tail

Comparative EmbryologyComparative Embryology

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Vestigial Vestigial StructuresStructures

Remnants of anatomical

features

Once served important

functions in an organism’s ancestors

Ex: spurs of pythons

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97

Molecular Molecular HomologiesHomologies

Genes inherited from a common ancestor that are

shared among organisms

Ex: Hemoglobin

98

Homologies Homologies and “Tree and “Tree Thinking”Thinking”

Evolutionary trees are used to explain

homologies

Hypotheses about relationships among

different groups

Constructed using anatomical & DNA

sequence data 99

100

101

Branch point

Lungfishes

Amphibians

Mammals

Lizards

and snakes

Crocodiles

Ostriches

Hawks and

other birds

Feathers

Amnion

Digit-

bearing

limbs

Homologous

characteristic

Tetra

po

ds

Am

nio

tes

Bird

s

1

2

3

4

5

6

Convergent EvolutionConvergent Evolution Melbourne, AustraliaMelbourne, Australia

102

Convergent Convergent EvolutionEvolution

Similar features (analogous traits)

can evolve in distantly related

groups

Arise when groups independently

adapt to similar environments in

similar ways

Convergent evolution does not

provide information about ancestry

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104

Sugar

glider

Flying

squirrel

NORTH

AMERICA

AUSTRALIA

105

DiacodexisDiacodexis, an early even, an early even--toed ungulatetoed ungulate

106

Most mammals Cetaceans and even-toed ungulates

(a) Canis (dog) (b) Pakicetus (c) Sus (pig) (d) Odocoileus (deer)

107

Other even-toed ungulates

Hippopotamuses

†Pakicetus

†Rodhocetus

†Dorudon

Living cetaceans

Common ancestor of cetaceans

Millions of years ago

70 Key 60 50 40 30 20 10 0 Pelvis Tibia

Femur Foot

BiogeographyBiogeography

The geographic distribution of

species

Major influence on Darwin’s theory

Islands have many endemic species closely related to

species on the nearest island or

mainland 108

Mangrove island research, FL KeysMangrove island research, FL Keys E.O. WilsonE.O. Wilson 109

Continental Continental DriftDrift

Earth’s continents were once united in a super-continent

called Pangaea

Have since separated by

continental drift

Understanding impact on species distribution helps predict when & where different groups evolved

110

What is a Theory?What is a Theory? What is a Theory?What is a Theory?

Broad and general

Supported by lots of evidence

Generates new

testable hypotheses

111

Darwin’s Theory Darwin’s Theory of Evolution by of Evolution by

Natural Natural SelectionSelection

Integrates diverse areas of biological

study

Ongoing research has only advanced

& strengthened our understanding

of evolution

Stimulates many new research

questions 112

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