Mechanisms of Evolution

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Mechanisms of Evolution
AP Biology Chapter 22
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Endless Forms Most Beautiful

• A new era of biology began in 1859 when Charles
  Darwin published The Origin of Species
• The Origin of Species focused biologists
  attention on the great diversity of organisms

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• Darwin noted that current species are descendants
  of ancestral species
• Evolution can be defined by Darwins phrase
  descent with modification
• Species are descendants of ancestral species that
  were different from the present-day species

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giant sloths to small sloths

• Height up to 20? Weight up to 10 lbs.
  Lifespan 30-40 years

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More narrow definition

• Evolution is a change in the genetic
  composition of a population from generation to
  generation

Did Darwin know this?
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• Evolution can be viewed as both a pattern and a
  process
• pattern - data accumulated
• process - mechanisms in place to
• cause change

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Prevailing ideas about the origin of life

• Species were fixed and individually created
• The earth was only 6000 years old

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Climate of the times
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
1900
1850
1800
1750
1795
Hutton proposes his theory of gradualism.
1798
Malthus publishes Essay on the Principle of
Population.
1809
Lamarck publishes his hypothesis of evolution.
1830
Lyell publishes Principles of Geology.
18311836
Darwin travels around the world on HMS Beagle.
1837
1837
Darwin begins his notebooks.
1844
Darwin writes essay on descent with modification.
1858
Wallace sends his hypothesis to Darwin.
1859
The Origin of Species is published.
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People and ideas that influenced Darwin
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• 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

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• Carolus Linnaeus interpreted 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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Fig. 22-3
The study of fossils helped to lay the groundwork
for Darwins ideas
Layers of deposited sediment
Younger stratum with more recent fossils
Older stratum with older fossils
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• 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

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• Geologists James Hutton and Charles Lyell
  perceived that changes in Earths surface can
  result from slow continuous actions still
  operating today. Hutton called his ideas
  gradualism.
• Lyells principle of uniformitarianism states
  that the mechanisms of change are constant over
  time
• This view strongly influenced Darwins thinking

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• Lamarck hypothesized that species evolve through
  use and disuse of body parts and the inheritance
  of acquired characteristics
• The mechanisms he proposed are unsupported by
  evidence
• However, he did come up
• with a mechanism for
• evolution.

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Was Lamarck totally wrong?
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A study shows that when mice are taught to fear
an odor, both their offspring and the next
generation are born fearing it. The gene for an
olfactory receptor activated by the odor is
specifically demethylated in the germ line and
the olfactory circuits for detecting the odor are
enhanced.
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About Darwin

• 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 for a 5-year around the world voyage
  on the Beagle

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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
Fig. 22-5
GREAT BRITAIN
EUROPE
NORTH AMERICA
ATLANTIC OCEAN
The Galápagos Islands
AFRICA
Pinta
Genovesa
Equator
Marchena
SOUTH AMERICA
Santiago
Daphne Islands
AUSTRALIA
Pinzón
Fernandina
PACIFIC OCEAN
Cape of Good Hope
Andes
Isabela
Santa Cruz
Santa Fe
San Cristobal
Tasmania
Florenza
Española
Cape Horn
New Zealand
Tierra del Fuego
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Fig. 22-6
(a) Cactus-eater
(c) Seed-eater
He noticed how finches beaks were adapted
for their diet.
(b) Insect-eater
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• 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 Darwins
• 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 lifes unity
  and diversity
• Natural selection is a cause of adaptive
  evolution
• In the Darwinian view, the history of life is
  like a tree with branches representing lifes
  diversity
• Darwins theory meshed well with the hierarchy of
  Linnaeus

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Fig. 22-7
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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)
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104
5.5
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2
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Millions of years ago
Years ago
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Adaptations

• 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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What is the ultimate source of variations in
natural populations?
MUTATIONS
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• 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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• Observation 4 Owing to lack of food or other
  resources, many of these offspring do not survive

My idea Precisely!
MALTHUS
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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 (fitness)
• Inference 2 This unequal ability of individuals
  to survive and reproduce will lead to the
  accumulation of favorable traits in the
  population over generations
• Favorable NOT BEST NECESSARILY

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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

Struggle for survival
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• 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
  speciesNature selects individuals to survive.
  Individuals do not change to survive.

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Fig. 22-12
(a) A flower mantid in Malaysia
(b) A stick mantid in Africa
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What is the relationship between evolution and
natural selection?

• Natural selection is one mechanism that can
  result in the process of evolution.

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One more important thing.

• Populations evolve, NOT INDIVIDUALS!
• Natural selections acts on individuals but the
  population as a whole evolves!

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Evidences for Evolution

• Direct observations
• The Fossil Record
• Homology
• Biogeography

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1. Direct Evidences Today

• Ex- Evidence of Drug-resistant HIV
• Ex Evidence of Drug-resistant bacteria such as
  MRSA
• Ex Evidence of Pesticide-resistant insects
• Coloration patterns in guppies due to predation

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Fig. 22-14
100
Patient No. 1
Patient No. 2
75
Percent of HIV resistant to 3TC
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Patient No. 3
25
0
2
0
4
6
8
10
12
Weeks
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2. Fossil Evidence

• 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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Fig. 22-15
0
2
4
4
Bristolia insolens
6
4
Bristolia bristolensis
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3
10
12
Depth (meters)
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Bristolia harringtoni
2
14
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Bristolia mohavensis
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1
3
2
Latham Shale dig site, San Bernardino County,
California
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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)
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3. Homology

• Homology is similarity resulting from common
  ancestry
• Can be both anatomical and molecular
• Anatomical similarities seen in comparative
  embryology suggest common ancestry

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Homologous structures are anatomical resemblances
that represent variations on a structural theme
present in a common ancestor
Fig. 22-17
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Whale
Cat
Bat
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Fig. 22-18
Pharyngeal pouches
Post-anal tail
Human embryo
Chick embryo (LM)
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• Vestigial structures are remnants of features
  that served important functions in the organisms
  ancestors
• Examples of homologies at the molecular level are
  genes shared among organisms inherited from a
  common ancestor

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Examples of homologies at the molecular level are
genes shared among organisms inherited from a
common ancestor
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• Convergent evolution is the evolution of similar,
  or analogous, features in distantly related
  groups
• Analogous - having the same function but not
  necessarily evolutionarily related.

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

• Darwins 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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Bird Biogeography
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• Phylogeny the evolutionary history of an
  organism
• Evolutionary trees show common ancestry and
  homologous structures linking organisms.

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Evolutionary Tree
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Is natural selection the ONLY mechanism
responsible for evolution?