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Chapter 22
Descent with Modification:
Darwinian View of Life
A
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
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Scala Naturae and Classification of Species
The Greek philosopher Aristotle viewed
species as fixed and arranged them on a
scala naturae (scale of nature)
The Old Testament holds that species
were individually designed by God and
therefore perfect
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Methods of Classification
Early Classification:
(384-322BC)
Aristotle was one of
the first people to
classify things
He noticed that living
organisms could be
grouped into 2
categories:
plants and animals
Aristotle
He noticed plants were green and didn’t move
And
Animals weren’t green and did move
Organizing Life’s Diversity
The History of Classification
 Animals were classified according to the
presence or absence of “red blood.”
 Animals were further grouped according to
their habitats and morphology.
 Plants were classified by average size and
structure as trees, shrubs, or herbs.
Aristotle
Next, he divided all the animals into three groups BASED
ON WHERE THEY LIVE
Animals that live in water
Animals that live on land
Animals that live in the air and could fly
Aristotle
Next, he worked out a
system of grouping for
plants:
He based this on the size of
the plant and the
pattern of growth
Tall plants with one
trunk were put in the
tree group
Medium plants with
many trunks were
considered shrubs
Small plants with soft
stems went into an herb
group
The Beginning of Modern
Classification
As scientists
discovered more
living things,
Aristotles way of
classifying
things became
less useful
So, in 1735,
Carolus Linnaeus
developed a new
classification
system
• Carolus Linnaeus interpreted organismal
adaptations as evidence that the Creator
had designed each species for a specific
purpose
• Linnaeus was the founder of taxonomy, the
branch of biology concerned with classifying
organisms
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Linnaeus
He grouped living
things into two
main
categories
He called these
groups
kingdoms
Kingdoms: the
largest group
of living things
Linnaeus
Animals were one
Kingdom
Plants were another
He placed organisms
with similar traits into
the same group and
called this group a
species. He used
very specific traits for
his groups.
Linnaeus
He grouped similar species into a larger group called a
genus.
Linnaeus
Important changes that Linnaeus made to Aristotle’s
system
1. He classified plants and animals into more groups
2. he based his system on specific traits
3. he gave organisms names that
traits
described their
Classification
Domain (the largest grouping)
Kingdom
Phylum
Class
Order
Family
Genus
Species
(the smallest group)
Scientific Names Come From
Classification
Scientific Name: the genus and species
names together
Genus name is always capitalized
species name is small print
always italicized or underlined (only if
handwritten)
Homo sapiens
Why Scientific Names Are Used
1.
No mistake can be made about what you are talking
about (two different living things don’t have the same
genus AND species names)
2.
Scientific names seldom change
3.
Written in the same language around the world (Latin)
Organizing Life’s Diversity
Modern Classification
Typological Species Concept
 Aristotle and Linnaeus thought of each
species as a distinctly different group of
organisms based on physical similarities.
 Based on the idea that species are
unchanging, distinct, and natural types.
The changes that
occur over time
in the hereditary
features of a
species.
Darwin noted that current species are
descendants of ancestral species
Evolution can be defined by Darwin’s
phrase descent with modification
Evolution can be viewed as both a
pattern and a process
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Fig. 22-1
Fig. 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)
Wallace (evolution, natural selection)
American Revolution
French Revolution
U.S. Civil War
1800
1900
1750
1850
1795Hutton proposes his theory of gradualism.
1798Malthus publishes “Essay on the Principle of Population.”
1809Lamarck publishes his hypothesis of evolution.
1830Lyell publishes Principles of Geology.
Darwin travels around the world on HMS Beagle.
1831–1836
1837Darwin begins his notebooks.
1844Darwin writes essay on descent with modificat
1858Wallace sends his hypothesis to Darwin
1859The Origin of Species is published.
Ideas About Change over Time
• 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
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Fig. 22-3
Layers of deposited
sediment
Younger stratum
with more recent
fossils
Older stratum
with older fossils
 Paleontology, the study of
fossils, was largely developed
by French scientist Georges
Cuvier (1769-1832)
 He noticed that the older
layers had fossils that were
dissimilar to (then) current
life forms.
 Cuvier advocated
catastrophism, speculating
that each boundary between
strata represents a
catastrophe
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Geologists James Hutton and Charles
Lyell perceived that changes in Earth’s
surface can result from slow continuous
actions still operating today
Lyell’s principle of uniformitarianism
states that the mechanisms of change
are constant over time
This view strongly influenced Darwin’s
thinking
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Lamarck’s Hypothesis of Evolution
 Lamarck hypothesized
that species evolve
through use and disuse
of body parts and the
inheritance of acquired
characteristics
(acquired
characteristics)
 The mechanisms he
proposed are
unsupported by
evidence
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Fig. 22-4
Concept 22.2: Descent with modification by
natural selection explains the adaptations of
organisms and the unity and diversity of life
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
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Darwin’s Research
As a boy and into adulthood,
Charles Darwin had a
consuming interest in nature
Darwin first studied medicine
(unsuccessfully), and then
theology at Cambridge
University
After graduating, he took an
unpaid position as naturalist
and companion to Captain
Robert FitzRoy for a 5-year
around the world voyage on
the Beagle
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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
Darwin was influenced by Lyell’s
Principles of Geology and thought that
the earth was more than 6000 years old
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His interest in geographic distribution of
species was kindled by a stop at the
Galápagos Islands near the equator west
of South America
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Evolution
Darwin’s Theory of Natural Selection
The Galápagos Islands
§Darwin began to collect mockingbirds,
finches, and other animals on the four
islands.
§He noticed that the different islands
seemed to have their own, slightly different
varieties of animals.
Evolution
Darwin’s Theory of Natural Selection
The Origin of Species
§Darwin published On the Origin of Species
by Means of Natural Selection in 1859.
§Darwin’s theory of natural selection is not
synonymous with evolution.
§It is a means of explaining how evolution
works.
Darwin’s Work
Important Ideas about
natural selection:
1. Living things
overproduce
2. There is
variation among the
offspring
A variation: is a
trait that makes
an individual
different from
others of its
species
Darwin’s Work
3. There is a struggle
to survive
There are more
living things than
resources to support
them. The result is
competition.
Competition is the
struggle among
living things to get
their needs for life.
Darwin’s Work
4.
Natural selection is always taking place.
Evolution is a change in the hereditary features of a group
of organisms over time.
Fig. 22-5
GREAT
BRITAIN
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
AFRICA
Pinta
Marchena
Santiago
Fernandina
Genovesa
Daphne
Islands
Pinzón
Isabela Santa
Santa
Cruz
San
Fe
Cristobal
Florenza Española
Equator
SOUTH
AMERICA
PACIFIC
OCEAN
Cape Horn
Tierra del Fuego
AUSTRALIA
Cape of
Good Hope
Tasmania
New
Zealand
Fig. 22-5a
Darwin in 1840
Fig. 22-5b
The
Galápagos
Islands
Pinta
Marchena
Santiago
Fernandina
Pinzón
Genovesa
Daphne
Islands
Isabela Santa Santa
Cruz
San
Fe
Cristobal
Florenza Española
Video: Galápagos Islands Overview
Video: Blue-footed Boobies Courtship Ritual
Video: Albatross Courtship Ritual
Video: Galápagos Sea Lion
Video: Soaring Hawk
Video: Galápagos Tortoises
Video: Galápagos Marine Iguana
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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
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Fig. 22-6
(a) Cactus-eater
(b) Insect-eater
(c) Seed-eater
Fig. 22-6a
(a) Cactus-eater
Fig. 22-6b
(b) Insect-eater
Fig. 22-6c
(c) Seed-eater
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
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The Origin of Species
Darwin developed two main ideas:
 Descent with modification explains life’s unity and diversity
 Natural selection is a cause of adaptive evolution
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Descent with Modification
Darwin never used the word evolution in
the first edition of The Origin of Species
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
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In the Darwinian view, the history of life is
like a tree with branches representing life’s
diversity
Darwin’s theory meshed well with the
hierarchy of Linnaeus
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-7
Fig. 22-8
Hyracoidea
(Hyraxes)
Sirenia
(Manatees
and relatives)
Moeritherium
Barytherium
Deinotherium
Mammut
Platybelodon
Stegodon
Mammuthus
Elephas maximus
(Asia)
Loxodonta
africana
(Africa)
Loxodonta cyclotis
(Africa)
34
24
Millions of years ago
5.5
2 1040
Years ago
Fig. 22-8a
Platybelodon
Stegodon
Mammuthus
Elephas maximus
(Asia)
Loxodonta
africana
(Africa)
Loxodonta cyclotis
(Africa)
34
24
Millions of years ago
5.5 2 1040
Years ago
Phylogenic Species Concept
 Phylogeny is the evolutionary history of a
species.
 The phylogenic species concept defines a
species as a cluster of organisms that is
distinct from other clusters and shows
evidence of a pattern of ancestry and
descent.
Characters
 To classify a species, scientists construct
patterns of descent by using characters.
 Characters can be morphological or
biochemical.
Artificial Selection, Natural Selection,
and Adaptation
Darwin noted that
humans have modified
other species by
selecting and breeding
individuals with
desired traits, a
process called
artificial selection
Darwin then described
four observations of
nature and from these
drew two inferences
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Observation #1: Members of a population
often vary greatly in their traits
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Fig. 22-10
Observation #2: Traits are inherited from
parents to offspring
Observation #3: All species are capable
of producing more offspring than the
environment can support
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Fig. 22-11
Spore
cloud
Observation #4: Owing to lack of food or
other resources, many of these offspring
do not survive
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Inference #1: Individuals whose inherited
traits give them a higher probability of
surviving and reproducing in a given
environment tend to leave more offspring
than other individuals
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Inference #2: This unequal ability of
individuals to survive and reproduce will
lead to the accumulation of favorable
traits in the population over generations
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Darwin was influenced by Thomas
Malthus who noted the potential for
human population to increase faster than
food supplies and other resources
If some heritable traits are
advantageous, these will accumulate in
the population, and this will increase the
frequency of individuals with adaptations
This process explains the match between
organisms and their environment
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Natural Selection: A Summary
Individuals with certain heritable
characteristics survive and reproduce at a
higher rate than other individuals
Natural selection increases the adaptation of
organisms to their environment over time
If an environment changes over time,
natural selection may result in adaptation to
these new conditions and may give rise to
new species
Video: Seahorse Camouflage
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Fig. 22-12
(a) A flower mantid
in Malaysia
(b) A stick mantid
in Africa
Fig. 22-12a
(a) A flower mantid
in Malaysia
Fig. 22-12b
(b) A stick mantid
in Africa
Note that individuals do not evolve;
populations evolve over time
Natural selection can only increase or
decrease heritable traits in a population
Adaptations vary with different
environments
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Co-Evolution
The term is used to
describe cases
where two (or
more) species
reciprocally affect
each other's
evolution
Coevolution
 Yucca moths and yucca
plants Yucca flowers are a
certain shape so only that
tiny moth can pollinate
them. The moths lay their
eggs in the yucca flowers
and the larvae
(caterpillars) live in the
developing ovary and eat
yucca seeds.
Let’s Watch Mr. Anderson blog
about Plants
http://www.youtube.com/watch?v=X
4L3r_XJW0I
Concept 22.3: Evolution is supported by
an overwhelming amount of scientific
evidence
New discoveries continue to fill the gaps
identified by Darwin in The Origin of Species
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Direct Observations of Evolutionary
Change
 Two examples provide evidence for natural
selection: the effect of differential predation on
guppy populations and the evolution of drugresistant HIV
 Sexual Selection
 Natural Selection (through predation/environment)
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Predation and Coloration in Guppies :
Scientific Inquiry
John Endler has studied
the effects of predators on
wild guppy populations
Brightly colored males are
more attractive to females
However, brightly colored
males are more vulnerable
to predation
Guppy populations in
pools with fewer predators
had more brightly colored
males
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Endler transferred brightly colored
guppies (with few predators) to a pool
with many predators
As predicted, over time the population
became less brightly colored
Endler also transferred drab colored
guppies (with many predators) to a pool
with few predators
As predicted, over time the population
became more brightly colored
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The Evolution of Drug-Resistant HIV
The use of drugs to combat HIV selects for
viruses resistant to these drugs
HIV uses the enzyme reverse transcriptase
to make a DNA version of its own RNA
genome
The drug 3TC is designed to interfere and
cause errors in the manufacture of DNA
from the virus
(it inserts itself where a cytosine should bethus stopping mitosis)
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Some individual HIV viruses have a
variation that allows them to produce DNA
without errors
These viruses have a greater reproductive
success and increase in number relative to
the susceptible viruses
The population of HIV viruses has therefore
developed resistance to 3TC
The ability of bacteria and viruses to evolve
rapidly poses a challenge to our society
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Fig. 22-14
100
Patient
No. 1
Patient No. 2
75
50
Patient No. 3
25
0
0
2
4
6
Weeks
8
10
12
Natural selection does not create new
traits, but edits or selects for traits
already present in the population
The local environment determines which
traits will be selected for or selected
against in any specific population
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The Fossil Record (more evidence for
evolution)
The fossil record provides evidence of the
extinction of species, the origin of new
groups, and changes within groups over
time
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Evolution
Evidence of Evolution
Support for Evolution
§ The fossil record
§ Fossils provide a record of species that lived long ago.
§ Fossils show that ancient species share similarities
with species that now live on Earth. (we can see that
changes occur).
Glyptodont
Armadillo
Fossil Evidence
Fossils are the remains of
once-living things from
ages past.
(footprints, bones,
skeletons, amber etc)
An extinct life-form is one
that no longer exists
Fossil Evidence
Fossils are found in Earth’s crust. They are found in
sedimentary rocks.
Sedimentary rocks form from layers of mud, sand, and
other fine particles.
Fossil Evidence
Scientist can tell how old fossils
are by dating them (with
radioactive isotopes). Being
able to date fossils gives
scientists an idea of the
history of life on Earth.
Fig. 22-15
0
2
4
4
6
4 Bristolia insolens
8
3 Bristolia bristolensis
10
12
3
2 Bristolia harringtoni
14
16
18 1 Bristolia mohavensis
3
2
1
Latham Shale dig site, San
Bernardino County, California
Depth (meters)
Fig. 22-15b
12
2
Bristolia harringtoni
14
16
18 1 Bristolia mohavensis
2
1
Latham Shale dig site, San
Bernardino County, California
Fig. 22-15c
0
4
3
Depth (meters)
2
4
6
4 Bristolia insolens
8
3 Bristolia bristolensis
10
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
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Fig. 22-16
(a) Pakicetus (terrestrial)
(b) Rhodocetus (predominantly aquatic)
Pelvis and
hind limb
(c) Dorudon (fully aquatic)
Pelvis and
hind limb
(d) Balaena
(recent whale ancestor)
Fig. 22-16ab
(a) Pakicetus (terrestrial)
(b) Rhodocetus (predominantly aquatic)
Fig. 22-16cd
Pelvis and
hind limb
(c) Dorudon (fully aquatic)
Pelvis and
hind limb
(d) Balaena
(recent whale ancestor)
Evolution
Evidence of Evolution
§Derived traits are newly evolved features,
such as feathers, that do not appear in the
fossils of common ancestors.
§Ancestral traits are more primitive features,
such as teeth and tails, that do appear in
ancestral forms.
Homology
Homology is similarity resulting from
common ancestry
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Homologous structures
§ Anatomically similar structures inherited from a common ancestor
are called homologous structures.
Anatomical and Molecular Homologies
Homologous structures are anatomical
resemblances that represent variations on a
structural theme present in a common
ancestor
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Fig. 22-17
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
Evidence of Evolution
§ Analogous structures can be
used for the same purpose
and can be superficially
similar in construction, but are
not inherited from a
common ancestor.
§ Show that
functionally similar
features can evolve
independently in
similar environments
Comparative embryology reveals anatomical
homologies not visible in adult organisms
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Comparative Embryology
If you look at
different
animals during
stages of
embryonic
development
you can see
common traits.
This shows a
common
ancestry.
Fig. 22-18
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Human embryo
Fig. 22-18a
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Fig. 22-18b
Pharyngeal
pouches
Post-anal
tail
Human embryo
HOX genes
 A group of related
genes that are
responsible for
determining the
basic structure and
orientation of body
structures for
different organisms
including humans,
flies, worms
 Highly conserved
throughout many
organisms
Evolution
Evidence of Evolution
Vestigial Structures
§Structures that are the
reduced forms of
functional structures in
other organisms.
Evolutionary theory
predicts that features of
ancestors that no longer
have a function for that
species will become
smaller over time until they
are lost.
Many animals still have
Those parts and still
use them.
Evolution
Evidence of Evolution
Comparative Biochemistry
§Common ancestry
can be seen in the
complex metabolic
molecules that many
different organisms
share.
 The similar appearance of chromosomes
among
chimpanzees,
gorillas, and
orangutans
suggests a
shared
ancestry.
Examples of homologies at the molecular
level are genes shared among organisms
inherited from a common ancestor
(like the HOX genes)
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Molecular Clocks
 Scientists use molecular
clocks to compare the
DNA sequences or amino
acid sequences of genes
that are shared by
different species.
 The differences between
the genes indicate the
presence of mutations.
 The more mutations that
have accumulated, the
more time that has
passed since
divergence.
Biochemical Characters
 Scientists use biochemical characters, such
as amino acids and nucleotides, to help
them determine evolutionary relationships
among species.
 DNA and RNA analyses are powerful tools
for reconstructing phylogenies.
Evolution
Evidence of Evolution
§Comparisons of the similarities in these
molecules across species reflect
evolutionary patterns seen in comparative
anatomy and in the fossil record.
§Organisms with closely related
morphological (body) features have more
closely related molecular (like DNA)
features.
Homologies and “Tree Thinking”
The Darwinian concept of an
evolutionary tree of life can explain
homologies
Evolutionary trees are hypotheses about
the relationships among different groups
Evolutionary trees can be made using
different types of data, for example,
anatomical and DNA sequence data
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Fig. 22-19
Branch point
(common ancestor)
Lungfishes
Amphibians
1
Mammals
2
Tetrapod limbs
Amnion
Lizards
and snakes
3
4
Homologous
characteristic
Crocodiles
Ostriches
6
Feathers
Hawks and
other birds
Birds
5
Convergent Evolution
Convergent evolution is the evolution
of similar, or analogous, features in
distantly related groups
Analogous traits arise when groups
independently adapt to similar
environments in similar ways
Convergent evolution does not provide
information about ancestry
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Fig. 22-20
Sugar
glider
NORTH
AMERICA
AUSTRALIA
Flying
squirrel
Biogeography
Darwin’s observations of biogeography,
the geographic distribution of species,
formed an important part of his theory of
evolution
Islands have many endemic species that
are often closely related to species on
the nearest mainland or island
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Earth’s continents were formerly united
in a single large continent called
Pangaea, but have since separated by
continental drift
An understanding of continent movement
and modern distribution of species allows
us to predict when and where different
groups evolved
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What Is Theoretical About Darwin’s 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
Ongoing research adds to our
understanding of evolution
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-UN1
Observations
Individuals in a population
vary in their heritable
characteristics.
Organisms produce more
offspring than the
environment can support.
Inferences
Individuals that are well suited
to their environment tend to leave
more offspring than other individuals
and
Over time, favorable traits
accumulate in the population.
Fig. 22-UN2
Fig. 22-UN3
You should now be able to:
1. Describe the contributions to
evolutionary theory made by Linnaeus,
Cuvier, Lyell, Lamarck, Malthus, and
Wallace
2. Describe Lamarck’s theories, and
explain why they have been rejected
3. Explain what Darwin meant by “descent
with modification”
4. List and explain Darwin’s four
observations and two inferences
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5. Explain why an individual organism
cannot evolve
6. Describe at least four lines of evidence
for evolution by natural selection
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings