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Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures forBio logy, Seventh Edi t ion

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 22

Descent with Modification: A

Darwinian View of Life

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Overview: Darwin Introduces a Revolutionary

Theory A new era of biology began on November 24,

1859

The day Charles Darwin published On theOrigin of Species by Means of NaturalSelection

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The Origin of Species

Focused biologists attention on the greatdiversity of organisms

Figure 22.1

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Darwin made two major points in his book

He presented evidence that the many speciesof organisms presently inhabiting the Earth aredescendants of ancestral species

He proposed a mechanism for the evolutionaryprocess, natural selection

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Concept 22.1: The Darwinian revolution

challenged traditional views of a young Earthinhabited by unchanging species

In order to understand why Darwins ideas

were revolutionary We need to examine his views in the context of

other Western ideas about Earth and its life

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The historical context of Darwins life and ideas

Figure 22.2

Linnaeus (classification)Hutton (gradual geologic change)

Lamarck (species can change)

Malthus (population limits)Cuvier (fossils, extinction)

Lyell (modern geology)

Darwin (evolution, nutural selection)Mendel (inheritance)

Wallace (evolution, natural selection)

1750

American Revolution French Revolution U.S. Civil War1800 1850 1900

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 1836 Darwin travels around the world on HMS Beagle. Darwin begins his notebooks on the origin of species.1837

Darwin writes his essay on the origin of species.1844Wallace sends his theory to Darwin.1858The Origin of Species is published.1859

Mendel publishes inheritance papers.1865

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Resistance to the Idea of Evolution


Shook the deepest roots of Western culture Challenged a worldview that had been

prevalent for centuries

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The Scale of Nature and Classification of Species

The Greek philosopher Aristotle

Viewed species as fixed and unchanging

The Old Testament of the Bible

Holds that species were individually designedby God and therefore perfect

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Carolus Linnaeus

Interpreted organismal adaptations asevidence that the Creator had designed eachspecies for a specific purpose

Was a founder of taxonomy, classifying lifesdiversity for the greater glory of God

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Fossils, Cuvier, and Catastrophism

The study of fossils

Helped to lay the groundwork for Darwins ideas

Fossils are remains or traces of organismsfrom the past

Usually found in sedimentary rock, which appearsin layers or strata

Figure 22.3

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Paleontology, the study of fossils

Was largely developed by French scientistGeorges Cuvier

Cuvier opposed the idea of gradualevolutionary change And instead advocated catastrophism,

speculating that each boundary betweenstrata represents a catastrophe

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Theories of Gradualism

Gradualism

Is the idea that profound change can takeplace through the cumulative effect of slow butcontinuous processes

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Geologists Hutton and Lyell

Perceived that changes in Earths surface canresult from slow continuous actions stilloperating today

Exerted a strong influence on Darwins thinking

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Lamarcks Theory of Evolution

Lamarck hypothesized that species evolve

Through use and disuse and the inheritance ofacquired traits

But the mechanisms he proposed areunsupported by evidence

Figure 22.4

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Concept 22.2: In The Origin of Species , Darwin

proposed that species change through naturalselection

As the 19th century dawned

It was generally believed that species hadremained unchanged since their creation, but amajor change would challenge this thinking

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Darwins Research

As a boy and into adulthood, Charles Darwin

Had a consuming interest in nature

Soon after Darwin received his B.A. degree

He was accepted on board the HMS Beagle ,which was about to embark on a voyagearound the world

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The Voyage of the Beagle

During his travels on the Beagle

Darwin observed and collected manyspecimens of South American plants andanimals

Darwin observed various adaptations of plantsand animals

That inhabited many diverse environments

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Darwins interest in the geographic distribution

of species Was kindled by the Beagle s stop at the Galpagos

Islands near the equator west of South America

Figure 22.5

England EUROPENORTH

AMERICA

GalpagosIslands

Darwin in 1840,after his return

SOUTH AMERICA

Cape ofGood Hope

Cape Horn

Tierra del Fuego

AFRICA HMS Beagle in port

AUSTRALIA

TasmaniaNewZealand

PACIFICOCEAN

A n

d e s

ATLANTICOCEAN

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Darwins Focus on Adaptation

As Darwin reassessed all that he had observed

during the voyage of the Beagle He began to perceive adaptation to the

environment and the origin of new species asclosely related processes

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From studies made years after Darwinsvoyage

Biologists have concluded that this is indeedwhat happened to the Galpagos finches

Figure 22.6a c

(a) Cactus eater. The long,sharp beak of the cactusground finch ( Geospizascandens ) helps it tearand eat cactus flowersand pulp.

(c) Seed eater. The large groundfinch ( Geospiza magnirostris )has a large beak adapted forcracking seeds that fall fromplants to the ground.

(b) Insect eater. The green warblerfinch ( Certhidea olivacea ) uses its

narrow, pointed beak to grasp insects.

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In 1844, Darwin wrote a long essay on theorigin of species and natural selection

But he was reluctant to introduce his theorypublicly, anticipating the uproar it would cause

In June 1858 Darwin received a manuscriptfrom Alfred Russell Wallace

Who had developed a theory of naturalselection similar to Darwins

Darwin quickly finished The Origin of Species

And published it the next year

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Darwin developed two main ideas

Evolution explains lifes unity and diversity Natural selection is a cause of adaptive

evolution

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Descent wi th M odification

The phrase descent with modification

Summarized Darwins perception of the unityof life

States that all organisms are related throughdescent from an ancestor that lived in theremote past

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

With multiple branchings from a common trunkto the tips of the youngest twigs that representthe diversity of living organisms

Figure 22.7

Hyracoidea(Hyraxes)

Sirenia(Manateesand relatives)

Elephasmaximus

(Asia)

Loxodontaafricana(Africa)

Loxodontacyclotis(Africa)

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Observation #1: For any species, populationsizes would increase exponentially

If all individuals that are born reproducedsuccessfully

Figure 22.8

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Observation #4: Members of a population varyextensively in their characteristics

No two individuals are exactly alike

Figure 22.9

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Observation #5: Much of this variation isheritable

Inference #2: Survival depends in part oninherited traits

Individuals whose inherited traits give them ahigh probability of surviving and reproducingare likely to leave more offspring than otherindividuals

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Inference #3: This unequal ability of individualsto survive and reproduce

Will lead to a gradual change in a population,with favorable characteristics accumulatingover generations

f l l

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Artificial Selection

In the process of artificial selection

Humans have modified other species overmany generations by selecting and breedingindividuals that possess desired traits

Figure 22.10

Terminalbud

Lateralbuds

Brussels sproutsCabbage

Flowercluster

Leaves

Cauliflower

Flowerandstems

Broccoli Wild mustard Kohlrabi

Stem

Kale

S f N l S l i

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Summary of Natural Selection

Natural selection is differential success inreproduction

That results from the interaction betweenindividuals that vary in heritable traits and theirenvironment

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Natural selection can produce an increase over time

In the adaptation of organisms to theirenvironment

Figure 22.11

(a) A flower mantidin Malaysia

(b) A stick mantidin Africa

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If an environment changes over time

Natural selection may result in adaptation tothese new conditions

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Concept 22.3: Darwins theory explains a widerange of observations

Darwins theory of evolution

Continues to be tested by how effectively it canaccount for additional observations andexperimental outcomes

N t l S l ti i A ti

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Natural Selection in Action

Two examples

Provide evidence for natural selection

Diff ti lP d ti i G P l ti

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Differential Predation in Guppy Popul ations

Researchers have observed natural selection

Leading to adaptive evolution in guppypopulations

Reznick and Endler transplanted guppies from pike-cichlid pools to killifish poolsand measured the average age and size of guppies at maturity over an 11-year period (30 to60 generations).

EXPERIMENT

Pools with killifish,but not guppies priorto transplant

Experimentaltransplant ofguppiesPredator: Killifish; preys

mainly on small guppies

Guppies:Larger atsexual maturitythan those inpike -cichlid pools

Predator: Pike-cichlid; preys mainly on large guppies

Guppies: Smaller at sexual maturity thanthose in killifish pools

Figure 22.12

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RESULTS After 11 years, the average size and age at maturity of guppies in the transplantedpopulations increased compared to those of guppies in control populations.

161.5185.6

67.5

92.3

48.5

Control Population: Guppiesfrom pools with pike-cichlidsas predators

Experimental Population:Guppies transplanted to

pools with killifish aspredators

76.1

Males Females

85.7

58.2

Males Females

CONCLUSION Reznick and Endler concluded that the change in predator resulted in different variationsin the population (larger size and faster maturation) being favored. Over a relatively short time, this alteredselection pressure resulted in an observable evolutionary change in the experimental population.

The E ol tion of Dr g Resistant HIV

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The Evolution of Drug-Resistant HIV

In humans, the use of drugs

Selects for pathogens that through chancemutations are resistant to the drugs effects

Natural selection is a cause of adaptiveevolution

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Researchers have developed numerous drugsto combat HIV

But using these medications selects forviruses resistant to the drugs

Figure 22.13

PatientNo. 1

Patient No. 2

Patient No. 3

Weeks

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The ability of bacteria and viruses to evolverapidly

Poses a challenge to our society

Homology Biogeography and the Fossil Record

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Homology, Biogeography, and the Fossil Record

Evolutionary theory

Provides a cohesive explanation for manykinds of observations

Homology

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Homology

Homology

Is similarity resulting from common ancestry

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Comparative embryology

Reveals additional anatomical homologies notvisible in adult organisms

Figure 22.15

Pharyngealpouches

Post-anal

tail

Chick embryo Human embryo

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Vestigial organs

Are some of the most intriguing homologousstructures

Are remnants of structures that served

important functions in the organismsancestors

Molecular Homologies

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Molecular Homologies

Biologists also observe homologies amongorganisms at the molecular level

Such as genes that are shared amongorganisms inherited from a common ancestor

Homologies and the Tree of Life

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Homologies and the Tree of Life

The Darwinian concept of an evolutionary treeof life

Can explain the homologies that researchershave observed

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Anatomical resemblances among species

Are generally reflected in their molecules, theirgenes, and their gene products

Figure 22.16

Species

Human

Rhesus monkey

Mouse

Chicken

Frog

Lamprey 14%

54%

69%

87%

95%

100%

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

Biogeography

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Biogeography

Darwins observations of the geographicdistribution of species, biogeography

Formed an important part of his theory ofevolution

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Sugarglider

AUSTRALIA

NORTH AMERICA

Flyingsquirrel

Figure 22.17

Some similar mammals that have adapted tosimilar environments

Have evolved independently from different ancestors

TheF ossilRecord

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The F ossil Record

The succession of forms observed in the fossilrecord

Is consistent with other inferences about themajor branches of descent in the tree of life

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The Darwinian view of life

Predicts that evolutionary transitions shouldleave signs in the fossil record

Paleontologists

Have discovered fossils of many suchtransitional forms

Figure 22.18

What Is Theoretical about the Darwinian View of Life?

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In science, a theory

Accounts for many observations and data andattempts to explain and integrate a greatvariety of phenomena

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Darwins theory of evolution by naturalselection

Integrates diverse areas of biological studyand stimulates many new research questions

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