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AP Biology
•Chapter 22~
•Descent with Modification:
A Darwinian View of Life
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Evolution
•Evolution:
the change over time of the
genetic composition of populations
•Natural selection:
populations of organisms can
change over the generations if individuals
having certain heritable traits leave more
offspring than others (differential
reproductive success)
•Evolutionary adaptations:
a prevalence
of inherited characteristics that enhance
organisms’ survival and reproduction
•November 24, 1859
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Overview: Endless Forms Most Beautiful
•The Origin of Species focused biologists’ attention on the great diversity of
organisms
•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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 22-2
In historical context
Other people’s
ideas paved the path for
Linnaeus (classification)
Darwin’s thinking
Hutton (gradual geologic change)
(population limits)
, extinction)
competition:
struggle for survival
population growth
exceeds food supply
land masses change over
immeasurable time
Scala Naturae and Classification of Species
• The Greek philosopher Aristotle viewed species as fixed
and arranged them on a scala naturae
• 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 the founder of taxonomy, the branch of
biology concerned with classifying organisms
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
• Cuvier advocated catastrophism, speculating
that each boundary between strata represents
a catastrophe
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• 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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Lamarck’s Hypothesis of Evolution
•Organisms adapted to
their environments
–
through acquired traits
–
change in their life time
• Use & Disuse
organisms lost parts because they did
not use them — like the missing eyes &
digestive system of the tapeworm
• Perfection with Use & Need
the constant use of an organ leads that
organ to increase in size — like the
muscles of a blacksmith or the large
ears of a night-flying bat
–
transmit acquired characteristics to next
generation
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Charles Darwin
•1809-1882
•British naturalist
•______________________
_______________________
_
•Collected clear evidence to
support his ideas
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Voyage of the HMS Beagle
•Invited to travel around the world
–
1831-1836 (22 years old!)
– makes many observations of nature
• main mission of the Beagle was to chart
South American coastline
•Robert Fitzroy
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 22-5
GREAT
BRITAIN
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
AFRICA
Pinta
Genovesa
Equator
Marchena
Santiago
Fernandina
Isabela
Daphne
Islands
Pinzón
Santa
Santa
Cruz
Fe
Florenza
SOUTH
AMERICA
AUSTRALIA
PACIFIC
OCEAN
San
Cristobal
Cape of
Good Hope
Tasmania
Española
Cape Horn
Tierra del Fuego
New
Zealand
Unique species
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Darwin found… birds
•Collected many different birds
on the Galapagos Islands.
•Thought he found
very different kinds…
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Finch?
Finch?
Sparrow?
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
Sparrow?
Woodpecker?
WleWarbler?
pecker?
r?
But Darwin found… a lot of finches
Darwin was amazed to
find out:
All 14 species of birds
were finches…
But there is only one species of
finch on the mainland!
F Large Ground
Finch
S Small Ground
QuickTime™ and a Finch parrow?
inch?
Photo - JPEG decompressor
are needed to see this picture.
How did
one species
of finches become
so many different
species now?
Woodpeck
Veg. Tree Finch
Warbler Finch
Warbler?
er?
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Tree Thinking
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Correlation of species to food source
Rapid speciation:
new species filling new niches,
because they inherited
successful adaptations.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Darwin’s finches
•Darwin’s conclusions
–
small populations of original South American finches land on islands
•
–
variation in beaks enabled individuals to gather food successfully in
the different environments
over many generations, the populations of finches changed anatomically
& behaviorally
___________________________________________
•emergence of different species
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
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
(a) Cactus-eater
c) Seed-eater
b) Insect-eater
In 1858, Darwin received a letter that changed
everything.
Alfred Russel Wallace
a young naturalist working
n the East Indies, had
written a short paper with a
new idea. He asked Darwin
o evaluate his ideas and
pass it along for publication.
November 24, 1859, Darwin published
On the Origin of Species by Means of Natural Selection”
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
•
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
More observations…
Correlation of species
to food source
Whoa,
Turtles, too!
Many islands also show
distinct local variations in
tortoise morphology…
…perhaps these are
the first steps in the
splitting of one species
into several?
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Selective breeding
the raw genetic material
(variation) is hidden
there
Four Observations
•Observation #1: Members of a population often vary
greatly in their traits
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• Observation #2: Traits are inherited from
parents to offspring
• Observation #3: All species are capable of
producing more offspring than the environment
can support
• Observation #4: Owing to lack of food or other
resources, many of these offspring do not
survive
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• 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
• Inference #2: This unequal ability of individuals
to survive and reproduce will lead to the
accumulation of favorable traits in the
population over generations
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• 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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 22-12
(a) A flower mantid
in Malaysia
(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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
• 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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 22-13
EXPERIMENT
Predator: Killifish; preys
mainly on juvenile
guppies (which do not
express the color genes)
Experimental
transplant of
guppies
Pools with
killifish,
but no
guppies prior
to transplant
Guppies: Adult males have
brighter colors than those
in “pike-cichlid pools”
Predator: Pike-cichlid; preys mainly on adult guppies
Guppies: Adult males are more drab in color
than those in “killifish pools”
RESULTS
12
Number of
colored spots
12
10
8
6
4
2
0
Source
population
Transplanted
population
10
8
6
4
2
0
Source
population
Transplanted
population
• 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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
•
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The Fossil Record
• The fossil record provides evidence of the
extinction of species, the origin of new groups,
and changes within groups over time
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
• 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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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)
Anatomical and Molecular Homologies
•Homology is similarity resulting from common ancestry
•Homologous structures are anatomical resemblances that represent variations
on a structural theme present in a common ancestor
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• Comparative embryology reveals anatomical
homologies not visible in adult organisms
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 22-18
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Human embryo
• Vestigial structures are remnants of features
that served important functions in the
organism’s ancestors
• Examples of homologies at the molecular level
are genes shared among organisms inherited
from a common ancestor
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
•
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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.