biol 102 chp 22 descent with modification: a darwinian view of life
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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
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1859: Charles Darwin 1859: Charles Darwin published published
The The Origin Origin of Species of Species
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Main Ideas Main Ideas of Evolutionof Evolution
Current species are descendants
of ancestral species
“Descent with modification”
Natural selection
DescendantsDescendants
AncestorAncestor 4
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Evolution accounts Evolution accounts for the unity & for the unity & diversity of lifediversity of life
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Theodosius Theodosius DobzhanskyDobzhansky
“Nothing in biology makes sense
except in the light of evolution.”
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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.
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Ancient ViewsAncient Views
Aristotle
Species are fixed & arranged on a scala
naturae
Old Testament
Species were individually designed
by God and, therefore, perfect
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ScalaScala NaturaeNaturae God in
Heaven
Angels
Humans
Animals
Plants
Rocks
Devil in Hell 10
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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
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Carl Carl LinneLinne “You can call me
Carolus Linnaeus”
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Species Genus Family Order Class Phylum Kingdom Domain Ursus americanus (American black bear) Ursus
Ursidae
Carnivora
Mammalia
Chordata
Animalia
Eukarya
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FossilsFossils
Remains or traces of organisms from
the past
Usually found in sedimentary rock
layers (strata)
Established the groundwork for Darwin’s ideas
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Younger stratum with more recent fossils
Layers of deposited sediment
Older stratum with older fossils
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SuedbergSuedberg Fossil PitFossil Pit Devonian 375 MYADevonian 375 MYA 22
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Geological Geological ViewsViews
Catastrophism Uniformitarianism
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CatastrophismCatastrophism
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Charles LyellCharles Lyell
Principles of GeologyPrinciples of Geology 27
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“The mechanisms of
“The mechanisms of
change are constant over
time”
UniformitarianismUniformitarianism
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“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
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JeanJean--BaptisteBaptiste LamarckLamarck
Species evolve through the use & disuse of body
parts
Characteristics acquired during life are inherited
Unsupported by evidence
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Lamarck’s HypothesisLamarck’s Hypothesis
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Aren’t you glad Aren’t you glad Lamarck Lamarck was wrong?was wrong? 33
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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
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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
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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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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
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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
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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
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SeedSeed--eatereater 43
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Adaptive Radiation of Galápagos FinchesAdaptive Radiation of Galápagos Finches
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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
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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
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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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Hyracoidea
(Hyraxes)
Sirenia (Manatees and relatives)
†Deinotherium
†Mammut
†Platybelodon
†Stegodon
†Mammuthus
Elephas maximus
(Asia)
Loxodonta africana
(Africa)
Loxodonta cyclotis
(Africa)
†Moeritherium
†Barytherium
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Millions of years ago
34 24 5.5 2 104 0
Years ago
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Artificial Artificial SelectionSelection
Darwin noted that humans have
modified other species
Select & breed individuals with
desired traits
Selective breeding =
artificial selection 54
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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
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Four Four Observations Observations
of Nature of Nature Made by Made by DarwinDarwin
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1.1. Members of a Members of a population often vary population often vary
greatly in their traitsgreatly in their traits 59
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2.2. Traits are Traits are inheritedinherited from from parents to offspringparents to offspring 61
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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
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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
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Two Inferences Two Inferences Made Made by Darwinby Darwin
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1. Individuals whose inherited traits give them
a higher probability of surviving & reproducing in an environment tend to leave more offspring
than others
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2. This unequal ability of individuals to survive & reproduce will lead to the accumulation of favorable traits in the
population over generations 66
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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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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
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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
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Limits of Limits of Natural Natural
SelectionSelection
Can only increase or decrease heritable
traits in a population
Individuals do not evolve…
Populations evolve
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Evolution is supported by Evolution is supported by an overwhelming amount an overwhelming amount of scientific evidenceof scientific evidence 74
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Tiktaalik the fishapod! 75
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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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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?
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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
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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
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Mosquito Resistance to DDTMosquito Resistance to DDT
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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
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Fossils as Fossils as EvidenceEvidence
Species extinction
Origin of new taxonomic
groups
Changes within groups over time
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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
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Bristolia harringtoni
Bristolia mohavensis
12
14
16
18
2
De
pth
(m
ete
rs)
1
1
2
85
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Transitional FormsTransitional Forms
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ArchaeopteryxArchaeopteryx 87
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(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
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(c)(c) DorudonDorudon (fully aquatic)(fully aquatic)
(d)(d) BalaenaBalaena (recent (recent whale ancestor)whale ancestor)
Pelvis and hind limb
Pelvis and hind limb
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HomologyHomology
Similarity resulting from common
ancestry
Homologous structures
Similarities that represent variations
on a structural theme found in a common ancestor 91
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Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
HumanHuman WhaleWhale CatCat BatBat
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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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Molecular Molecular HomologiesHomologies
Genes inherited from a common ancestor that are
shared among organisms
Ex: Hemoglobin
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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
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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
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Convergent EvolutionConvergent Evolution Melbourne, AustraliaMelbourne, Australia
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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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Sugar
glider
Flying
squirrel
NORTH
AMERICA
AUSTRALIA
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DiacodexisDiacodexis, an early even, an early even--toed ungulatetoed ungulate
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Most mammals Cetaceans and even-toed ungulates
(a) Canis (dog) (b) Pakicetus (c) Sus (pig) (d) Odocoileus (deer)
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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
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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
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Mangrove island research, FL KeysMangrove island research, FL Keys E.O. WilsonE.O. Wilson 109
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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
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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
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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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