ch 22 notes

PowerPoint Lectures for

Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 22

Descent with Modification: A

Darwinian View of Life

Overview: Darwin Introduces a Revolutionary Theory

• A new era of biology began on November 24,

1859, the day Charles Darwin published On the

Origin of Species by Means of Natural Selection

• The Origin of Species focused biologists’ attention

on the great diversity of organisms

Video: Galápagos Marine Iguana

• Darwin made two major points in his book:

– Many current species are descendants of

ancestral species

– Natural selection is a mechanism for this

evolutionary process

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

• To understand why Darwin’s ideas were

revolutionary, we must examine them in relation to

other Western ideas about Earth and its life

LE 22-2

Linnaeus (classification)

Hutton (gradual geologic change)

Lamarck (species can change)

Malthus (population limits)

Cuvier (fossils, extinction)

Lyell (modern geology)

Darwin (evolution, natural selection)

Mendel (inheritance)

Wallace (evolution, natural selection)

French Revolution U.S. Civil War

1900 1850 1800 1750

American Revolution

1795 Hutton proposes his theory of gradualism.

1798 Malthus publishes “Essay on the Principle of Population.”

1809 Lamarck publishes his theory of evolution.

1830 Lyell publishes Principles of Geology.

1831–1936 Darwin travels around the world on HMS Beagle.

1837 Darwin begins his notebooks on the origin of species.

1844 Darwin writes his essay on the origin of species.

1858 Wallace sends his theory to Darwin.

1859 The Origin of Species is published.

1865 Mendel publishes inheritance papers.

Resistance to the Idea of Evolution

• The Origin of Species

– Shook the deepest roots of Western culture

– Challenged a worldview that had been

prevalent for centuries

The Scale of Nature and Classification of Species

• The Greek philosopher Aristotle viewed species

as fixed and unchanging

• The Old Testament holds that species were

individually designed by God and therefore perfect

• Carolus Linnaeus interpreted organismal

adaptations as evidence that the Creator had

designed each species for a specific purpose

• Linnaeus was a founder of taxonomy, the branch

of biology concerned with classifying organisms

Fossils, Cuvier, and Catastrophism

• The study of fossils helped to lay the groundwork

for Darwin’s ideas

• Fossils are remains or traces of organisms from

the past, usually found in sedimentary rock, which

appears in layers or strata

Video: Grand Canyon

• Paleontology, the study of fossils, was largely

developed by French scientist Georges Cuvier

• Cuvier advocated catastrophism, speculating that

each boundary between strata represents a

catastrophe

Theories of Gradualism

• Gradualism is the idea that profound change can

take place through the cumulative effect of slow

but continuous processes

• Geologists Hutton and Lyell perceived that

changes in Earth’s surface can result from slow

continuous actions still operating today

• This view strongly influenced Darwin’s thinking

Lamarck’s Theory of Evolution

• Lamarck hypothesized that species evolve

through use and disuse and the inheritance of

acquired traits

• The mechanisms he proposed are unsupported by

evidence

Concept 22.2: In The Origin of Species, Darwin proposed that species change through natural selection

• As the 19th century dawned, it was generally

believed that species had remained unchanged

since their creation

• However, a few doubts about the permanence of

species were beginning to arise

Darwin’s Research

• As a boy and into adulthood, Charles Darwin had

a consuming interest in nature

• After receiving his B.A. degree, he was accepted

on board the HMS Beagle, which was embarking

on a voyage around the world

The Voyage of the Beagle

• During his travels on the Beagle, Darwin collected

specimens of South American plants and animals

• He observed adaptations of plants and animals

that inhabited many diverse environments

• His interest in geographic distribution of species

was kindled by a stop at the Galápagos Islands

near the equator west of South America

LE 22-5

AMERICA

AFRICA

EUROPE

AUSTRALIA

PACIFIC

ATLANTIC

England

Cape of

Good Hope

Cape Horn

Tierra del Fuego

Galápagos

Islands

Darwin in 1840, after his return

HMS Beagle in port

Equator

Tasmania

New Zealand

Video: Albatross Courtship Ritual

Video: Blue-footed Boobies Courtship Ritual

Video: Galápagos Island Overview

Video: Galápagos Sea Lion

Video: Soaring Hawk

Video: Galápagos Tortoise

Darwin’s Focus on Adaptation

• In reassessing his observations, Darwin perceived

adaptation to the environment and the origin of

new species as closely related processes

• From studies made years after Darwin’s voyage,

biologists have concluded that this is indeed what

happened to the Galápagos finches

LE 22-6

Cactus eater. The long, sharp beak of the cactus ground finch (Geospiza scandens) helps it tear and eat cactus flowers and pulp.

Seed eater. The large ground finch (Geospiza magnirostris) has a large beak adapted for cracking seeds that fall from plants to the ground.

Insect eater. The green warbler finch (Certhidea olivacea) used its narrow, pointed beak to grasp insects.

• In 1844, Darwin wrote an essay on the origin of

species and natural selection but did not introduce

his theory publicly, anticipating an uproar

• In June 1858, Darwin received a manuscript from

Alfred Russell Wallace, who had developed a

theory of natural selection similar to Darwin’s

• Darwin quickly finished The Origin of Species and

published it the next year

The Origin of Species

• Darwin developed two main ideas:

– Evolution explains life’s unity and diversity

– Natural selection is a cause of adaptive

evolution

Descent with Modification

• 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

• In the Darwinian view, the history of life is like a

tree with branches representing life’s diversity

LE 22-7

Hyracoidea

(Hyraxes)

Sirenia

(Manatees

and relatives) 0

10,000

Elephas maximus

(Asia)

Loxodonta africana (Africa)

Loxodonta cyclotis (Africa)

Natural Selection and Adaptation

• Evolutionary biologist Ernst Mayr has dissected

the logic of Darwin’s theory into three inferences

based on five observations

• Observation #1: For any species, population sizes

would increase exponentially if all individuals that

are born reproduced successfully

• Observation #2: Populations tend to be stable in

size, except for seasonal fluctuations

• Observation #3: Resources are limited

• Inference #1: Production of more individuals than

the environment can support leads to a struggle

for existence among individuals of a population,

with only a fraction of their offspring surviving

• Observation #4: Members of a population vary

extensively in their characteristics; no two

individuals are exactly alike

• Observation #5: Much of this variation is heritable

• Inference #2: Survival depends in part on inherited

traits; individuals whose inherited traits give them

a high probability of surviving and reproducing are

likely to leave more offspring than other individuals

• Inference #3: This unequal ability of individuals to

survive and reproduce will lead to a gradual

change in a population, with favorable

characteristics accumulating over generations

Artificial Selection

• In artificial selection, humans have modified other

species over many generations by selecting and

breeding individuals with desired traits

LE 22-10

Cabbage

Flower

clusters

Terminal

Lateral

Brussels sprouts

Leaves

Kohlrabi Wild mustard Broccoli

Cauliflower

Flowers

Summary of Natural Selection

• Natural selection is differential success in

reproduction from interaction between individuals

that vary in heritable traits and their environment

• Natural selection produces an increase over time

in adaptation of organisms to their environment

• If an environment changes over time, natural

selection may result in adaptation to these new

conditions

Video: Seahorse Camouflage

LE 22-11 A flower mantid in Malaysia

A stick mantid in Africa

Concept 22.3: Darwin’s theory explains a wide range of observations

• Darwin’s theory of evolution continues to be tested

by how effectively it can account for additional

observations and experimental outcomes

Natural Selection in Action

• Two examples provide evidence for natural

selection: the effect of differential predation on

guppy populations and the evolution of drug-

resistant HIV

Differential Predation in Guppy Populations

• Researchers have observed natural selection

leading to adaptive evolution in guppy populations

LE 22-12a

Predator: Killifish; preys

mainly on small guppies

Guppies:

Larger at

sexual maturity

than those in

“pike-cichlid pools”

Experimental

transplant of

guppies

Predator: Pike-cichlid; preys mainly on large guppies

Guppies: Smaller at sexual maturity than

those in “killifish pools”

Pools with killifish

but no guppies prior

to transplant

LE 22-12b

Control population:

Guppies from pools with

pike-cichlids as predators

Experimental population:

Guppies transplanted to

pools with killifish as

predators

Females

58.2 48.5

Females

76.1 67.5

The Evolution of Drug-Resistant HIV

• The use of drugs to combat HIV selects for viruses

resistant to these drugs

• The ability of bacteria and viruses to evolve rapidly

poses a challenge to our society

LE 22-13

Patient No. 3

Patient No. 2

Patient No. 1

0 2 4 6 8 10 12

Homology, Biogeography, and the Fossil Record

• Evolutionary theory provides a cohesive

explanation for many kinds of observations

Homology

• Homology is similarity resulting from common

ancestry

Anatomical Homologies

• Homologous structures are anatomical

resemblances that represent variations on a

structural theme present in a common ancestor

LE 22-14

Human Cat Whale Bat

• Comparative embryology reveals anatomical

homologies not visible in adult organisms

LE 22-15

Chick embryo (LM) Human embryo

Pharyngeal pouches

Post-anal tail

• Vestigial organs are remnants of structures that

served important functions in the organism’s

ancestors

Molecular Homologies

• Examples of homologies at the molecular level are

genes shared among organisms inherited from a

common ancestor

Homologies and the Tree of Life

• The Darwinian concept of an evolutionary tree of

life can explain homologies

• Anatomical resemblances among species are

generally reflected in their molecules, genes, and

gene products

LE 22-16

Percent of Amino Acids That Are

Identical to the Amino Acids in a

Human Hemoglobin Polypeptide

Rhesus monkey

Species

Chicken

Lamprey

Biogeography

• Darwin’s observations of biogeography, the

geographic distribution of species, formed an

important part of his theory of evolution

• Some similar mammals that have adapted to

similar environments have evolved independently

from different ancestors

LE 22-17

Sugar glider

Flying squirrel

NORTH AMERICA

AUSTRALIA

The Fossil Record

• The succession of forms observed in the fossil

record is consistent with other inferences about

the major branches of descent in the tree of life

• The Darwinian view of life predicts that

evolutionary transitions should leave signs in the

fossil record

• Paleontologists have discovered fossils of many

such transitional forms

What Is Theoretical about the Darwinian 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

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