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