Descent with Modification Descent with Modification Darwinian View of Life Darwinian View of Life Chapter 22
Jan 12, 2016
Descent with ModificationDescent with ModificationDarwinian View of LifeDarwinian View of Life
Descent with ModificationDescent with ModificationDarwinian View of LifeDarwinian View of Life
Chapter 22Chapter 22
Why is Evolution So Controversial?
Why is Evolution So Controversial?
Often evolution (and science in general) is pitted against religion in “winner take all” stance
Modern debate mostly involves the teaching of evolution rather than the theory itself
And that means mixing science, religion and politics, etc.---Never an easy combination!
Plenty of misconceptions and confusion surround evolution, adding to controversy
Often evolution (and science in general) is pitted against religion in “winner take all” stance
Modern debate mostly involves the teaching of evolution rather than the theory itself
And that means mixing science, religion and politics, etc.---Never an easy combination!
Plenty of misconceptions and confusion surround evolution, adding to controversy
3 Key Observations About Life3 Key Observations About Life
1.Organisms are suited for life in their environments.
2.Organisms share many characteristics of life (unity).
3.There is a rich diversity of life.
These observations led Charles Darwin to develop a scientific explanation for these observations.
1.Organisms are suited for life in their environments.
2.Organisms share many characteristics of life (unity).
3.There is a rich diversity of life.
These observations led Charles Darwin to develop a scientific explanation for these observations.
Endless Forms Most BeautifulEndless Forms Most Beautiful
• Study of biology upended in 1859 when Darwin published The Origin of Species
• Darwin proposed: Descent with modification
• Species are descendants of ancestral species which were different from present day species
• Evolution: change in genetic composition of population from generation to generation
• Study of biology upended in 1859 when Darwin published The Origin of Species
• Darwin proposed: Descent with modification
• Species are descendants of ancestral species which were different from present day species
• Evolution: change in genetic composition of population from generation to generation
Summary of Other Ideas Summary of Other Ideas
• Many scientists before and during the time of Darwin theorized on what was the cause of the unity and diversity of living organisms
• Some ideas supported Darwin’s theories while some did not
• Many scientists before and during the time of Darwin theorized on what was the cause of the unity and diversity of living organisms
• Some ideas supported Darwin’s theories while some did not
Intellectual Context of Darwin’s Ideas1809
1798
1812
1795
1830
17901809 183136
1844
18591870
Lamarck publishes hishypothesis of evolution.
Malthus publishes“Essay on the Principle
of Population.”
Hutton proposeshis principle of
gradualism.
Charles Darwinis 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 hypothesisof natural selection.
1858Cuvier publishes his extensive studies of vertebrate fossils.
Lyell publishesPrinciples of Geology.
Not in Darwin’s “Camp”Not in Darwin’s “Camp”
• Aristotle viewed species as unchanging
• Arranged them on a scala naturae, ladder of permanent “rungs”
• Linneaus: Developed taxonomy and the binomial classification system
• Believed in a divine placement of organisms in this classification, not necessarily changing either
• Cuvier (geologist): Founded of modern paleontology (study of fossils)
• Saw that fossils are deposited in strata (layers) of rocks with older layers containing fossils of species that may be extinct now
• Believed in catastrophism, the sudden loss of local species due to disasters
• Aristotle viewed species as unchanging
• Arranged them on a scala naturae, ladder of permanent “rungs”
• Linneaus: Developed taxonomy and the binomial classification system
• Believed in a divine placement of organisms in this classification, not necessarily changing either
• Cuvier (geologist): Founded of modern paleontology (study of fossils)
• Saw that fossils are deposited in strata (layers) of rocks with older layers containing fossils of species that may be extinct now
• Believed in catastrophism, the sudden loss of local species due to disasters
Lamarck’s Hypothesis of EvolutionLamarck’s Hypothesis of Evolution
• Other scientists were thinking about life forms evolving over
time
• Lamarck hypothesized:
• Use and disuse of body parts could change organisms over their
lifespan
• These changes could be passed to offspring by Inheritance of
Acquired Characteristics
Lamarck’s Hypothesis of EvolutionLamarck’s Hypothesis of Evolution
• Lamarckism unsupported by much of
genetic evidence
• BUT emerging field of epigenetics may prove
to support some of Larmarck’s ideas!
Scientists in Darwin’s “Camp”Scientists in Darwin’s “Camp”
• Hutton and Lyell believed:
• Earth’s surface changes from cumulative, SLOW continuous actions still operating today (uniformitarianism)
• Strongly influenced Darwin’s thinking
• He reasoned the Earth must be much older than previously believed
• Also reasoned biological organisms may also have slow, continuous change
• Malthus (economist):
• Limited resources shape population sizes
• Hutton and Lyell believed:
• Earth’s surface changes from cumulative, SLOW continuous actions still operating today (uniformitarianism)
• Strongly influenced Darwin’s thinking
• He reasoned the Earth must be much older than previously believed
• Also reasoned biological organisms may also have slow, continuous change
• Malthus (economist):
• Limited resources shape population sizes
Voyage of the HMS Beagle
Darwin in 1840, after his return from the voyage
TheGalápagosIslands
NORTHAMERICA
ATLANTICOCEAN
PACIFICOCEAN
PACIFICOCEAN
Pinta
MarchenaGenovesa
Equator
Chile
SantiagoDaphneIslands
Fernandina
Isabela SantaCruz
SantaFe San
Cristobal
EspañolaKilometers
0 20 40 Florenza
Pinzón
SOUTHAMERICA
AFRICA
EUROPEGreatBritain
HMS Beagle in port
Equator
PACIFICOCEAN
Malay Archipelago
AUSTRALIA
Tasmania
NewZealand
Brazil
Argentina
Cape Horn
An
des
Mtn
s.
Cape ofGood Hope
Darwin’s Focus on AdaptationDarwin’s Focus on Adaptation
• During the voyage, Darwin observed many
adaptations:
• Inherited characteristics of organisms which increase
their survival and reproduction in different
environments
• Darwin saw how adaptation to environment and
the origin of species is closely related
• Theorized: Could new species arise from gradual
accumulation of adaptations to different
environments?
Darwin’s Focus on AdaptationDarwin’s Focus on Adaptation
How do adaptations arise? Largely
dependent on:
Natural selection: Process in which
individuals with certain inherited traits
tend to survive and reproduce at higher
rates than other individuals because of
those traits
Example of Speciation in Galapagos Finches
(a) Cactus-eater (b) Insect-eater
(c) Seed-eater
Artificial SelectionArtificial Selection
• Humans have modified other species by selective
breeding for 1000’s of years, a process called artificial
selection
The Reason Why You Shouldn’t ProcrastinateThe Reason Why You Shouldn’t Procrastinate
• In 1844, Darwin wrote an essay on natural
selection--but did not publicize it
• In June 1858, Wallace sent Darwin a paper to
review with an almost identical theory of natural
selection
• Darwin quickly finished The Origin of Species by
Means of Natural Selection and published it
• Wallace graciously stepped away so now we call it
“Darwinism” and not “Wallacism”!
Observations of DarwinObservations of Darwin
• Observation #1: Members of a population
often vary in their inherited traits
Observations of DarwinObservations of Darwin
Observation #2: All species can produce more
offspring than the environment can support
• Many offspring fail to survive and reproduce
Important Points About Natural SelectionImportant Points About Natural Selection
• Note that individuals do not evolve; but
populations evolve over time
• Natural selection can only increase or
decrease heritable traits that vary in a
population
• If everyone is genetically identical, no basis for
selection
• Adaptations vary with different environments
• Single adaptation not preferred for all
environments
Direct Observations of Evolutionary ChangeDirect Observations of Evolutionary Change
• The bacterium Staphylococcus aureus is
commonly found on people
• One strain, methicillin-resistant S. aureus (MRSA)
is a dangerous pathogen
• S. aureus became resistant to penicillin in
1945 and resistant to methicillin in 1961
Direct Observations of Evolutionary ChangeDirect Observations of Evolutionary Change
• Methicillin works by inhibiting a protein used by
bacteria in their cell walls
• But MRSA bacteria use a different protein in their cell
walls
• When exposed to methicillin, MRSA strains are
more likely to survive and reproduce than
nonresistant S. aureus strains
• MRSA strains are now resistant to many
antibiotics
HomologyHomology
• Homology is similarity resulting from
common ancestry
• Homologous structures are anatomical
resemblances that represent variations
on a structural theme present in a
common ancestor
Mammalian Forelimbs: Homologous Structures
Humerus
Radius
Ulna
Carpals
MetacarpalsPhalanges
Human Cat Whale Bat
Embryonic Homologies
Pharyngealpouches
Post-analtail
Chick embryo (LM) Human embryo
• Comparative embryology reveals anatomical
homologies not visible in adult organisms
Vestigial StructuresVestigial Structures
• Common human vestigial structures:
• Appendix
• Male nipples
• Wisdom teeth
• Body hair and goosebumps
• Ear muscles
• Vestigial structures are remnants of features that
served important functions in the organism’s ancestors
Evolutionary Tree
Branch pointLungfishes
Amphibians
Mammals
Lizardsand snakes
Crocodiles
Ostriches
Hawks andother birds
Feathers
Amnion
Digit-bearinglimbs
Homologouscharacteristic
Te
trap
od
s
Am
nio
tes
Bird
s
1
2
3
4
5
6
Different Cause of Resemblance: Convergent Evolution
Different Cause of Resemblance: Convergent Evolution
• Convergent evolution is the evolution of
similar, or analogous, features in distantly
related groups
• Analogous traits arise when groups independently
adapt to similar environments in similar ways
• Convergent evolution does not provide information
about ancestry
Examples of Convergent Evolution Examples of Convergent Evolution
Homology vs. Convergent EvolutionHomology vs. Convergent Evolution
• Both are evidence of evolution
• Analogous features (convergent evolution)
share similar function but not common
ancestry
• Homologous features (homology) share
common ancestry but not necessarily
similar function