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8/12/2019 Biology Chp 22
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Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint Lectures forBio logy, Seventh Edit 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 the
Origin of Species by Means of Natural
Selection
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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 are
descendants of ancestral species
He proposed a mechanism for the evolutionaryprocess, natural selection
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Concept 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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Concept 2: In The Origin of Species, Darwin
proposed that species change through naturalselection
As the 19th century dawned
It was generally believed that species had
remained unchanged since their creation, but a
major change would challenge this thinking
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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 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.
18311836 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
TheOrigin of Speciesis published.1859
Mendel publishes inheritance papers.1865
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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
Plato believed in two worlds: one real world that is
ideal and perfect and an illusory world of
imperfection that we perceive through our senses.
Aristotle believed that all living forms could bearranged on a ladder (scala naturae) of increasing
complexity with every rung taken with perfect,
permanent species.
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Carolus Linnaeus
Interpreted organismal adaptations asevidence that the Creator had designed each
species for a specific purpose
Was a founder of taxonomy, classifying lifesdiversity for the greater glory of God
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The Old Testament account of creation
fortified the idea that species wereindividually designed and did not evolve.
In the 1700s, the dominant philosophy,
natural theology, was dedicated to studyingthe adaptations of organisms as evidence
that the Creator had designed each species
for a purpose.
Darwins views were influenced by fossils,
the relics or impressions of organisms from
the past, mineralized in sedimentary rocks.
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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 organisms
from the past
Usually found in sedimentary rock, which appears
in layers or strata
Figure 22.3
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HOW are fossils made?
Sedimentary rocks form when mud and sand
settle to the bottom of seas, lakes, and marshes.
New layers of sediment cover older ones,
creating layers of rock called strata.
Fossils within layers show that a succession of
organisms have populated Earth throughout
time.
Fig. 22.2 Fig. 22.4
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Paleontology, the study of fossils, was largely
developed by Georges Cuvier, a French
anatomist.
In particular, Cuvier documented the
succession of fossil species in the Paris Basin.
Cuvier recognized that extinction had been a commonoccurrence in the history of life.
Instead of evolution, Cuvier advocated catastrophism,
that boundaries between strata were due to local flood
or drought that destroyed the species then present.
Later, this area would be repopulated by species
immigrating from other unaffected areas.
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Theories of gradualism and uniformitarianism
In contrast to Cuviers catastrophism, James
Hutton, a Scottish geologist, proposed that thediversity of landforms (e.g., canyons) could be
explained by mechanisms currentlyoperating.
Hutton proposed a theory of gradualism, thatprofound change results from slow, continuous
processes.
Later, Charles Lyell proposed a theory ofuniformitarianism, that geological processes
had not changed throughout Earths history.
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Rates of evolutionary change (Old and New concepts
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Huttons and Lyells observations and theories
had a strong influence on Darwin.
First, if geologic changes result from slow,
continuous processes, rather than sudden
events, then the Earth must be far older than
the 6,000 years assigned by theologians frombiblical inference.
Second, slow and subtle processes persisting
for long periods of time can add up tosubstantial change.
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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 are
unsupported by evidence
Figure 22.4
L k l d f il i l i
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In 1809, Jean Baptiste Lamarck published a
theory of evolution based on his observationsof fossil invertebrates in the Natural History
Museum of Paris.
Lamarck thought that he saw what appeared tobe several lines of descent in the collected
fossils and current species.
Each was a chronological series of older to
younger fossils leading to a modern species.
Lamarck placed fossils in an evolutionary context
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C f
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Central to Lamarcks mechanism of evolution
* concepts of use and disuse of parts and of
inheritance of acquired characteristics. The former proposed that body parts used extensively
to cope with the environment became larger and
stronger, while those not used deteriorated.
The latter proposed that modifications acquired during
the life of an organism could be passed to offspring.
A classic example of these is the long neck of the giraffe in
which individuals could acquire longer necks by reaching forleaves on higher branches and would pass this characteristic to
their offspring.
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Lamarcks theory was a visionary attempt to
explain both the fossil record and the current
diversity of life through its recognition of thegreat age of Earth and adaptation of organisms
to the environment.
However, there is no evidence that acquired
characteristics can be inherited.
Acquired traits (e.g., bigger biceps) do not
change the genes transmitted by gametes to
offspring.
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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 HMSBeagle,which was about to embark on a voyage
around 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 and
animals
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 Beagles stop at the Galpagos
Islands near the equator west of South America
Figure 22.5
England EUROPENORTH
AMERICA
Galpagos
Islands
Darwin in 1840,
after his return
SOUTHAMERICA
Cape of
Good Hope
Cape Horn
Tierra del Fuego
AFRICA HMS Beagle in port
AUSTRALIA
TasmaniaNew
Zealand
PACIFIC
OCEAN
Andes
ATLANTIC
OCEAN
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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 as
closely related processes
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From studies made years after Darwins
voyage
Biologists have concluded that this is indeed
what happened to the Galpagos finches
Figure 22.6ac
(a) Cactus eater.The long,
sharp beak of the cactusground finch (Geospiza
scandens) helps it tear
and eat cactus flowers
and pulp.
(c) Seed eater.The large ground
finch (Geospiza magnirostris)
has a large beak adapted for
cracking seeds that fall from
plants to the ground.
(b) Insect eater.The green warbler
finch (Certhidea olivacea) uses its
narrow, pointed beak to grasp insects.
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Fig. 1.17b
The finches of the Galapagos Islandsdiversified after an initial colonization from themainland to exploit different food sources on
different islands.
py g , , p g j g
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In 1844, Darwin wrote a long essay on the
origin of species and natural selection
But he was reluctant to introduce his theory
publicly, anticipating the uproar it would cause
In June 1858 Darwin received a manuscriptfrom Alfred Russell Wallace
Who had developed a theory of natural
selection similar to Darwins
Darwin quickly finished The Origin of Species
And published it the next year
Th O i i f S i
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The Origin of Species
Darwin developed two main ideas
Evolution explains lifes unity and diversity
Natural selection is a cause of adaptive
evolution
D t i th M dif i ti
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Descent wi th Modif ication
The phrase descent with modification
Summarized Darwins perception of the unityof life
States that all organisms are related through
descent 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 represent
the diversity of living organisms
Figure 22.7
Hyracoidea
(Hyraxes)
Sirenia(Manatees
and relatives)
Elephasmaximus
(Asia)
Loxodontaafricana
(Africa)
Loxodontacyclotis
(Africa)
N t l S l ti d Ad t ti
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Natural Selection and Adaptation
Evolutionary biologist Ernst Mayr has dissected
the logic of Darwins theory into three
inferences based on five observations
Observation #1: For any species, population
sizes would increase exponentially If all individuals that are born are able to
reproduced successfully
Birth rate is more than death rate
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Observation #2: Nonetheless, 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 amongindividuals of a population, with only a fraction
of their offspring surviving
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Observation #4: Members of a population vary
extensively in their characteristics
No two individuals are exactly alike
Figure 22.9
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Observation #5: Much of this variation is
heritable
Inference #2: Survival depends in part on
inherited traits
Individuals whose inherited traits give them ahigh probability of surviving and reproducing
are likely to leave more offspring than other
individuals
Survival of the fittest? Or the luckiest?
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Survival of the fittest? Or the luckiest?
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
Affected by natural and artifical selective
pressures- predation, mate choice, diseases
Fig. 1.15
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Copyright
2002 Pearson
Education,
Inc.,
publishing as
Benjamin
Cummings
Artificial Selection
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Artificial Selection
In the process of artificial selection
Humans have modified other species overmany generations by selecting and breeding
individuals that possess desired traits
Figure 22.10
Terminalbud
Lateralbuds
Brussels sproutsCabbage
Flower
clusterLeaves
Cauliflower
Flower
and
stems
Broccoli Wild mustard Kohlrabi
Stem
Kale
Summary of Natural Selection
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Summary of Natural Selection
Natural selection is differential success in
reproduction
That results from the interaction between
individuals that vary in heritable traits and their
environment
If an environment changes over time
Natural selection may result in adaptation to
these new conditions
Mimicry and camouflage
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Mimicry and camouflage
Natural selection can produce an increase over time
In the adaptation of organisms to theirenvironment
Figure 22.11
(a) A flower mantid
in Malaysia
(b) A stick mantid
in Africa
Differential Predation in Guppy Populations
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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
guppiesPredator: 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
Guppy data analysis
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Guppy data analysis
RESULTSAfter 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
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
CONCLUSIONReznick 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.
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Example of adaptation and evolution in Drug use
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Example of adaptation and evolution in Drug use
Researchers have developed numerous drugs
to combat HIV
But using these medications selects for
viruses resistant to the drugs
Figure 22.13
PatientNo. 1
Patient No. 2
Patient No. 3
Weeks
Homology Biogeography and the Fossil Record
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Homology, Biogeography, and the Fossil Record
Evolutionary theory take into account:
Homology-- Is similarity resulting from commonancestry
Comparative embryology
Vestigial organs
Molecular homologies
Biogeography-- the geographic distribution ofspecies,
Fossil record
Anatomical Homologies
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Anatomical Homologies
Homologous structures between organisms
Are anatomical resemblances that representvariations on a structural theme that was
present in a common ancestor
Figure 22.14
Human Cat Whale Bat
Comparative embryology
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Comparative embryology
Reveals additional anatomical homologies not
visible in adult organisms
Figure 22.15
Pharyngealpouches
Post-anal
tail
Chick embryo Human embryo
Ontogeny repeats Phylogeny
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Ontogeny repeats Phylogeny
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Molecular Homologies
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Molecular Homologies
Biologists also observe
homologies among
organisms at the molecularlevel
Such as genes that
are shared among
organisms inherited
from a common
ancestor
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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
Lamprey14%
54%
69%
87%
95%
100%
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide
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Example of the Evolutionary tree of life on Earth
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Example of the Evolutionary tree of life on Earth
The tree assumes that
all life in the planetevolved from ONE
common ancestor:1) Implies that we are all
related to each other
2) That all creatures sharesimilar characteristics
3) That life as we know it had
one sourceGod, ET or
chance?
Biogeography
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Sugar
glider
AUSTRALIA
NORTH
AMERICA
Flying
squirrel
Figure 22.17
Biogeography
Some similar mammals that have adapted to
similar environments
Have evolved independently from different ancestors
The Fossil Record
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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
Transitional forms
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The Darwinian view of life
Predicts thatevolutionary
transitions should
leave signs in the
fossil record
Paleontologists
Have discovered
fossils of many such
transitional forms
Figure 22.18
lungfish
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Ancient walking fish
The Coelecanth
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Records and PROOF
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What can affect these records? What can not be recorded?
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 great
variety of phenomena
Darwins theory of evolution by naturalselection
Integrates diverse areas of biological study
and stimulates many new research questions
Still has many unanswered questions that is
why it is still a THEORY!!!!