22_lecture_presentation_0 (1).ppthhbhhhhjhbh

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
EVOLUTION
12/04/24

Overview: Endless Forms Most Beautiful
• A new era of biology began in 1859 when Charles
Darwin published The Origin of Species which
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.

Intellectuals / Ideas in Darwin’s Era
American Revolution French Revolution U.S. Civil War
1900
1850
1800
1750
1795
1809
1798
1830
1831–1836
1837
1859
1837
1844
1858
The Origin of Species is published.
Wallace sends his hypothesis to Darwin.
Darwin begins his notebooks.
Darwin writes essay on descent with modification.
Darwin travels around the world on HMS Beagle.
Malthus publishes “Essay on the Principle of Population.”
Lyell publishes Principles of Geology.
Lamarck publishes his hypothesis of evolution.
Hutton proposes his theory of gradualism.
Linnaeus (classification)
Cuvier (fossils, extinction)
Malthus (population limits)
Lamarck (species can change)
Hutton (gradual geologic change)
Lyell (modern geology)
Darwin (evolution, natural selection)
Wallace (evolution, natural selection)

• Carolus Linnaeus was the founder of taxonomy, the
branch of biology concerned with classifying
organisms.
• Paleontology, the study of fossils, was largely
developed by French scientist Georges Cuvier.
• 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.
Scientisits …

Fossils
Younger stratum
with more recent
fossils
Layers of deposited
sediment
Older stratum
with older fossils

Lamarck: Use & Disuse …
Darwin: Natural Selection ….
• Lamarck hypothesized that species evolve
through use and disuse of body parts and the
inheritance of acquired characteristics.
• 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’s Voyage on the Beagle
NORTH
AMERICA
EUROPE
AFRICA
AUSTRALIA
GREAT
BRITAIN
SOUTH
AMERICA
ATLANTIC
OCEAN
PACIFIC
OCEAN Cape of
Good Hope
Tierra del Fuego
Cape Horn
Tasmania
New
Zealand
An
de
s Equator
The
Galápagos
Islands
Pinta
Marchena
Genovesa
Santiago
Daphne
Islands
Pinzón
Fernandina
Isabela
San
Cristobal
Santa
Fe
Santa
Cruz
Florenza Española

Darwin’s Focus on Adaptation
• Darwin’s interest in geographic distribution of
species was kindled by a stop at the
Galápagos Islands near the equator west of
South America.
• Darwin perceived adaptation to the
environment and the origin of new species as
closely related processes.
• Recent biologists have concluded that
speciation is indeed what happened to the
Galápagos finches.

Speciation of Galapagos Finches
(a) Cactus-eater (c) Seed-eater
(b) Insect-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 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.

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.

Descent With
Modification
Hyracoidea
(Hyraxes)
Sirenia
(Manatees
and relatives)
Moeritherium
Barytherium
Deinotherium
Mammut
Elephas maximus
(Asia)
Stegodon
Mammuthus
Loxodonta
africana
(Africa)
Loxodonta cyclotis
(Africa)
0
104
2
5.5
24
34
Millions of years ago Years ago
Platybelodon

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.

Observation #1: Members of a population
often vary greatly in their traits.

• 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: Overproduction leads to
competition for food or other resources.
• The individuals best adapted to their
environment will survive and reproduce.

• 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.
Descent With Modification:

• 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 those adaptations.
• This process explains the match between
organisms and their environment.

Natural Selection: A Summary
• Survival of the Fittest: Individuals with
certain heritable adaptive characteristics
survive and reproduce at a higher rate than
other individuals.
• Natural selection increases the adaptation of
organisms to their environment over time.
• Speciation: If an environment changes over
time, natural selection may result in adaptation
to these new conditions and may give rise to
new species.

Predation and Coloration in Guppies : Scientific
Inquiry in Natural Selection
• 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.

Natural
Selection
Predator: Killifish; preys
mainly on juvenile
guppies (which do not
express the color genes)
Guppies: Adult males have
brighter colors than those
in “pike-cichlid pools”
Experimental
transplant of
guppies
Pools with
killifish,
but no
guppies prior
to transplant
Predator: Pike-cichlid; preys mainly on adult guppies
Guppies: Adult males are more drab in color
than those in “killifish pools”
Source
population
Transplanted
population
Source
population
Transplanted
population
Number
of
colored
spots
Area
of
colored
spots
(mm
2
)
12
12
10
10
8
8
6 6
4 4
2
2
0 0
RESULTS
EXPERIMENT

• 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.
Experiment in Natural Selection Results

Directional Natural Selection: 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 greater reproductive success.
• 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.
• 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.

Fossil
Evidence
of Change
Over Time
Bristolia insolens
Bristolia bristolensis
Bristolia harringtoni
Bristolia mohavensis
Latham Shale dig site, San
Bernardino County, California
Depth
(meters
)
0
2
4
6
8
10
12
14
16
18
1
2
3
3
3
1
2
4
4

Paleontologists
study fossils of
possible
transitional forms:
Whale
Ancestors
(a) Pakicetus (terrestrial)
(b) Rhodocetus (predominantly aquatic)
(c) Dorudon (fully aquatic)
Pelvis and
hind limb
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.

Homologous Structures
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human Whale
Cat Bat

Comparative embryology reveals anatomical homologies
not visible in adult organisms:
Human embryo
Chick embryo (LM)
Pharyngeal
pouches
Post-anal
tail

• 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.

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.

Homologies and “Evolutionary Tree”
Hawks and
other birds
Ostriches
Crocodiles
Lizards
and snakes
Amphibians
Mammals
Lungfishes
Tetrapod limbs
Amnion
Feathers
Homologous
characteristic
Branch point
(common ancestor)
Tetrapods
Amnio
tes
Birds
6
5
4
3
2
1

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.

Fig. 22-20
Sugar
glider
Flying
squirrel
AUSTRALIA
NORTH
AMERICA

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 (found
only in that part of the world and
nowhere else). Darwin postulated that
endemic species are often closely 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.

Darwin : Natural Selection
Observations
Over time, favorable traits
accumulate in the population.
Inferences
and
Individuals in a population
vary in their heritable
characteristics.
Organisms produce more
offspring than the
environment can support.
Individuals that are well suited
to their environment tend to leave
more offspring than other individuals

Mutation = Resistance to DDT. Natural Selection Favors this
Resistance --> Number of Resistant Individuals Increases Over Time.

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. Explain Darwin’s observations and inferences.
5. Explain why an individual organism cannot evolve.
6. Describe evidence for evolution by natural selection.

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