Descent with Modification:

A Darwinian View of Life

Chapter 22

LECTURE PRESENTATIONS

For CAMPBELL BIOLOGY, NINTH EDITION

Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson

© 2011 Pearson Education, Inc.

Lectures by

Erin Barley

Kathleen Fitzpatrick

Concept 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species

• Darwin noted that current species are descendants of ancestral species
• Evolution can be defined by Darwin’s phrase descent with modification
• Evolution can be viewed as both a pattern and a process
• Darwin’s ideas had deep historical roots

Figure 22.2

1809

1798

1812

1795

1830

1790

1809

1831−36

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.

• Carolus Linnaeus interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose
• Linnaeus was the founder of taxonomy, the branch of biology concerned with classifying organisms
• He developed the binomial format for naming species (for example, Homo sapiens)

Figure 22.3

Sedimentary rock

layers (strata)

Younger stratum

with more recent

fossils

Older stratum

with older fossils

Studies of Hutton, Lyell, and Lamarck

• Geologists James Hutton and Charles Lyell perceived that changes in Earth’s surface can result from slow continuous actions still operating today
• Lyell’s principle of uniformitarianism states that the mechanisms of change are constant over time
• This view strongly influenced Darwin’s thinking
• Lamarck hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics
• The mechanisms he proposed are unsupported by evidence

Figure 22.5

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

Andes Mtns.

Cape of

Good Hope

Concept 22.2: Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life

Figure 22.6

(a) Cactus-eater

(b) Insect-eater

(c) Seed-eater

The Origin of Species

• In 1844, Darwin wrote an essay on natural selection as the mechanism of descent with modification, but did not introduce his theory publicly
• Darwin explained three broad observations:
• The unity of life
• The diversity of life
• The match between organisms and their environment

Descent with Modification

• Darwin never used the word evolution in the first edition of The Origin of Species
• The phrase descent with modification summarized Darwin’s perception of the unity of life
• The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past

Figure 22.8

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

Artificial Selection, Natural Selection, and Adaptation

• Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection
• Darwin drew two inferences from two observations

Figure 22.UN02

Observations

Members of a population�often vary in their heritable�characteristics.

Organisms produce more�offspring than the�environment can support.

Individuals that are well suited�to their environment tend to leave�more offspring than other individuals.

Inferences

and

Over time, favorable traits�accumulate in the population.�

• Darwin was influenced by Thomas Malthus, who noted the potential for human population to increase faster than food supplies and other resources
• If some heritable traits are advantageous, these will accumulate in a population over time, and this will increase the frequency of individuals with these traits
• This process explains the match between organisms and their environment

Natural Selection: A Summary

• Individuals with certain heritable characteristics survive and reproduce at a higher rate than other individuals
• Natural selection increases the adaptation of organisms to their environment over time
• If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species

Video: Seahorse Camouflage

Concept 22.3: Evolution is supported by an overwhelming amount of scientific evidence

• New discoveries continue to fill the gaps identified by Darwin in The Origin of Species
• Direct Observations of Evolutionary Change
• Two examples provide evidence for natural selection: natural selection in response to introduced plant species, and the evolution of drug-resistant bacteria

​

Figure 22.13a

Soapberry bug with beak �inserted in balloon vine fruit

FIELD STUDY

• Soapberry bugs use their “beak” to feed on seeds within fruits
• In southern Florida soapberry bugs feed on balloon vine with larger fruit; they have longer beaks
• In central Florida they feed on goldenrain tree with smaller fruit; they have shorter beaks
• Correlation between fruit size and beak size has also been observed in Louisiana, Oklahoma, and Australia
• In all cases, beak size has evolved in populations that feed on introduced plants with fruits that are smaller or larger than the native fruits
• These cases are examples of evolution by natural selection
• In Florida this evolution in beak size occurred in less than 35 years

​

Natural Selection in Response to Introduced Plant Species

Figure 22.13b

On native species, �southern Florida

Museum-specimen average

On introduced species, �central Florida

Number of individuals

10

8

6

4

2

0

10

8

6

4

2

0

Beak

Beak length (mm)

6

7

8

10

11

RESULTS

9

The Evolution of Drug-Resistant Bacteria

• 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, two years after it was first widely used
• S. aureus became resistant to methicillin in 1961, two years after it was first widely used
• Methicillin works by inhibiting a protein used by bacteria in their cell walls
• 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

​

​

Figure 22.14

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

• Natural selection does not create new traits, but edits or selects for traits already present in the population
• The local environment determines which traits will be selected for or selected against in any specific population

Figure 22.15

Humerus

Radius

Ulna

Carpals

Metacarpals

Phalanges

Human

Cat

Whale

Bat

Homology is similarity resulting from common ancestry.

Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor.

Homology

Figure 22.16

Pharyngeal�pouches

Post-anal�tail

Chick embryo (LM)

Human embryo

• Comparative embryology reveals anatomical homologies not visible in adult organisms

• Vestigial structures are remnants of features that served important functions in the organism’s ancestors
• Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor

​

Homologies and “Tree Thinking”

• Evolutionary trees are hypotheses about the relationships among different groups
• Homologies form nested patterns in evolutionary trees
• Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data

Figure 22.17

Branch point

Lungfishes

Amphibians

Mammals

Lizards�and snakes

Crocodiles

Ostriches

Hawks and�other birds

Feathers

Amnion

Digit-�bearing

limbs

Homologous�characteristic

Tetrapods

Amniotes

Birds

Figure 22.18

Sugar�glider

Flying�squirrel

NORTH�AMERICA

AUSTRALIA

• 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

A Different Cause of Resemblance: Convergent Evolution

Figure 22.19

Most mammals

Cetaceans and even-toed ungulates

(a) Canis (dog)

(b) Pakicetus

(c) Sus (pig)

(d) Odocoileus (deer)

• The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time.

The Fossil Record

• Fossils can document important transitions
• For example, the transition from land to sea in the ancestors of cetaceans

Figure 22.20

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

Biogeography

• Biogeography, the geographic distribution of species, provides evidence of evolution
• Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift
• An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved

• Endemic species are species that are not found anywhere else in the world
• Islands have many endemic species that are often closely related to species on the nearest mainland or island
• Darwin explained that species on islands gave rise to new species as they adapted to new environments

What Is Theoretical About Darwin’s View of Life?

• In science, a theory accounts for many observations and data and attempts to explain and integrate a great variety of phenomena
• Darwin’s theory of evolution by natural selection integrates diverse areas of biological study and stimulates many new research questions
• Ongoing research adds to our understanding of evolution