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PowerPoint Lectures forBiology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 22

Descent with Modification: ADarwinian View of Life

•Overview: Darwin Introduces a RevolutionaryTheory

•A new era of biology began on November 24,1859

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

•The Origin of Species

–Focused biologists’ attention on the greatdiversity of organisms

Figure 22.1

•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

–EVOLUTION: change over time in geneticcomposition of a population.

•Concept 22.1: The Darwinian revolutionchallenged traditional views of a young Earthinhabited by unchanging species

•In order to understand why Darwin’s ideaswere revolutionary

–We need to examine his views in the context ofother Western ideas about Earth and its life

•The historical context of Darwin’s 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 War

1800

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.

1844

Wallace sends his theory to Darwin.

1858

The Origin of Species is published.

1859

Mendel publishes inheritance papers.

1865

Resistance to the Idea of Evolution

•The Origin of Species

–Shook the deepest roots of Western culture

–Challenged a worldview that had beenprevalent for centuries

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

•Carolus Linnaeus

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

–Was a founder of taxonomy, classifying life’sdiversity “for the greater glory of God”

–Binomial Nomenclature.

Fossils, Cuvier, and Catastrophism

•The study of fossils

–Helped to lay the groundwork for Darwin’s ideas

•Fossils are remains or traces of organismsfrom the past

–Usually found in sedimentary rock, which appearsin layers or strata

Figure 22.3

•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

Theories of Gradualism

•Gradualism

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

•Geologists Hutton and Lyell

–Perceived that changes in Earth’s surface canresult from slow continuous actions stilloperating today

–Exerted a strong influence on Darwin’s thinking

Lamarck’s 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

•Concept 22.2: In The Origin of Species, Darwinproposed 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

Darwin’s 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

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

•Darwin’s interest in the geographic distributionof species

–Was kindled by the Beagle’s stop at the GalápagosIslands near the equator west of South America

Figure 22.5

England

EUROPE

NORTH

AMERICA

Galápagos

Islands

Darwin in 1840,

after his return

SOUTH

AMERICA

Cape of

Good Hope

Cape Horn

Tierra del Fuego

AFRICA

HMS Beagle in port

AUSTRALIA

Tasmania

New

Zealand

PACIFIC

OCEAN

Andes

ATLANTIC

OCEAN

Darwin’s Focus on Adaptation

•As Darwin reassessed all that he had observedduring the voyage of the Beagle

–He began to perceive adaptation to theenvironment and the origin of new species asclosely related processes

•From studies made years after Darwin’svoyage

–Biologists have concluded that this is indeedwhat happened to the Galápagos 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 itsnarrow, pointed beak to grasp insects.

•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 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 adaptiveevolution

Descent with Modification

•The phrase descent with modification

–Summarized Darwin’s perception of the unityof life

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

•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

(Manatees

and relatives)

Years ago

Millions of years ago

Deinotherium

Mammut

Stegodon

Mammuthus

Platybelodon

Barytherium

Moeritherium

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 intothree inferences based on five observations

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

–If all individuals that are born reproducedsuccessfully

Figure 22.8

•Observation #2: Nonetheless, populations tendto be stable in size

–Except for seasonal fluctuations

•Observation #3: Resources are limited

•Inference #1: Production of more individualsthan the environment can support

–Leads to a struggle for existence amongindividuals of a population, with only a fractionof their offspring surviving

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

–No two individuals are exactly alike

Figure 22.9

•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

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

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

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

Terminal

bud

Lateral

buds

Brussels sprouts

Cabbage

Flower

cluster

Leaves

Cauliflower

Flower

and

stems

Broccoli

Wild mustard

Kohlrabi

Stem

Kale

Summary of Natural Selection

•Natural selection is differential success inreproduction

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

•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

•If an environment changes over time

–Natural selection may result in adaptation tothese new conditions

•Concept 22.3: Darwin’s theory explains a widerange of observations

•Darwin’s theory of evolution

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

Differential Predation in Guppy Populations

•Researchers have observed natural selection

–Leading to adaptive evolution in guppypopulations

Reznick and Endler transplanted guppies from pike-cichlid pools to killifish pools

and measured the average age and size of guppies at maturity over an 11-year period (30 to

60 generations).

EXPERIMENT

Pools with killifish,

but not guppies prior

to transplant

Experimental

transplant of

guppies

Predator: Killifish; preys

mainly on small guppies

Guppies:

Larger at

sexual maturity

than those in

“pike-cichlid pools”

Predator: Pike-cichlid; preys mainly on large guppies

Guppies: Smaller at sexual maturity than

those in “killifish pools”

Figure 22.12

RESULTS

After 11 years, the average size and age at maturity of guppies in the transplanted

populations increased compared to those of guppies in control populations.

161.5

185.6

67.5

Weight of guppies

at maturity (mg)

Age of guppies

at maturity (days)

92.3

48.5

Control Population: Guppies

from pools with pike-cichlids

as predators

Experimental Population:

Guppies transplanted to

pools with killifish as

predators

76.1

Males

Females

85.7

58.2

Males

Females

CONCLUSION

Reznick and Endler concluded that the change in predator resulted in different variations

in the population (larger size and faster maturation) being favored. Over a relatively short time, this altered

selection pressure resulted in an observable evolutionary change in the experimental population.

The Evolution of Drug-Resistant HIV

•In humans, the use of drugs

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

–The drug does not create resistant pathogens,it selects for resistant individuals alreadypresent in the population

•Natural selection is a cause of adaptiveevolution

•The ability of bacteria and viruses to evolverapidly

–Poses a challenge to our society

Homology, Biogeography, and the Fossil Record

•Evolutionary theory

–Provides a cohesive explanation for manykinds of observations

•Homology

–Is similarity resulting from common ancestry

Anatomical Homologies

•Homologous structures between organisms

–Are anatomical resemblances that representvariations on a structural theme that waspresent in a common ancestor

Figure 22.14

Human

Cat

Whale

Bat

•Comparative embryology

–Reveals additional anatomical homologies notvisible in adult organisms

Figure 22.15

Pharyngeal

pouches

Post-anal

tail

Chick embryo

Human embryo

•Vestigial organs

–Are some of the most intriguing homologousstructures

–Are remnants of structures that servedimportant functions in the organism’sancestors

Molecular Homologies

•Biologists also observe homologies amongorganisms at the molecular level

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

•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 Are

Identical to the Amino Acids in a

Human Hemoglobin Polypeptide

Biogeography

•Darwin’s observations of the geographicdistribution of species, biogeography

–Formed an important part of his theory ofevolution

–Species adapt to environment based on thegenes from ancestors

Sugar

glider

AUSTRALIA

NORTH

AMERICA

Flying

squirrel

Figure 22.17

•Some similar mammals that have adapted tosimilar environments

–Have evolved independently from different ancestors(Convergent evolution)

The Fossil Record

•The succession of forms observed in the fossilrecord

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

•Paleontologists

–Have discovered fossils of many suchtransitional forms

Figure 22.18

•Darwin’s theory of evolution by naturalselection

–Integrates diverse areas of biological studyand stimulates many new research questions