22 Lectures PPT

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 22Chapter 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 22-2LE 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 War1900185018001750

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 22-5LE 22-5

NORTHAMERICA

SOUTHAMERICA

AFRICA

EUROPE

AUSTRALIA

PACIFICOCEAN

ATLANTICOCEAN

England

Cape ofGood Hope

Cape Horn

Tierra del Fuego

GalápagosIslands

Darwin in 1840,after his return

HMS Beagle in port

Equator

Tasmania

NewZealand

An

des


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 22-6LE 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 22-7LE 22-7

Hyracoidea(Hyraxes)

Sirenia(Manatees

and relatives)

Yea

rs a

go

010,000

2

5.5

Mill

ion

s o

f ye

ars

ago

24

34

Mo

eri t

her

i um

Bar

yth

eriu

m

Dei

no

t her

ium

Mam

mu

t

Pl a

tyb

elo

do

n

St e

go

do

n

Mam

mu

t hu

s

Elephasmaximus

(Asia)

Loxodontaafricana(Africa)

Loxodontacyclotis(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 22-10LE 22-10

Cabbage

Flowerclusters

Terminalbud

Lateralbuds

Brussels sprouts

Leaves

Kale

Stem

KohlrabiWild mustardBroccoli

Cauliflower

Flowersandstems


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 22-11LE 22-11A flower mantidin Malaysia

A stick mantidin 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 22-12aLE 22-12a

Predator: Killifish; preysmainly on small guppies

Guppies: Larger atsexual maturitythan those in “pike-cichlid pools”

Experimentaltransplant ofguppies

Predator: Pike-cichlid; preys mainly on large guppies

Guppies: Smaller at sexual maturity thanthose in “killifish pools”

Pools with killifishbut no guppies priorto transplant

LE 22-12bLE 22-12b

Control population:Guppies from pools withpike-cichlids as predators

Experimental population:Guppies transplanted topools with killifish as predators

92.3

Females

Ag

e o

f g

up

pie

sat

mat

uri

ty (

day

s)Males

85.7

58.248.5

100

80

60

40

20

185.6

Females

Mas

s o

f g

up

pie

sat

mat

uri

ty (

mg

)

Males

161.5

76.167.5

200

160

120

80

40


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 22-13LE 22-13

Patient No. 3

Patient No. 2

Patient No. 1

100

75

50

25

00 2 4 6 8 10 12

Weeks

Per

cen

t o

f H

IV r

esis

tan

t to

3T

C


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 22-14LE 22-14

Human Cat Whale Bat


• Comparative embryology reveals anatomical homologies not visible in adult organisms

LE 22-15LE 22-15

Chick embryo (LM) Human embryo

Pharyngealpouches

Post-analtail


• 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 22-16LE 22-16

Percent of Amino Acids That AreIdentical to the Amino Acids in aHuman Hemoglobin Polypeptide

100%

95%

87%

69%

54%

14%

Rhesus monkey

Species

Human

Mouse

Chicken

Frog

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 22-17LE 22-17

Sugarglider

Flyingsquirrel

NORTHAMERICA

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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