Biology
Ch. 15 Notes
Tracing Evolutionary History
Opening Essay
Compare the structure of the wings of pterosaurs, birds,
and bats. Explain how the wings are based upon a
similar pattern.
15.1 Describe the current evidence supporting the idea
that life existed at least 3.5 billion years ago.
 Stromatolites: dense, layered mats of
photosynthetic prokaryotes found fossilized and dated
to 3.5 bya
 Photosynthesis is complex process
 Earlier processes were simpler, maybe 3.9 bya
15.1 Describe the four stages that might have produced
the first cells on Earth.
 Spontaneous Generation: life from non-living matter
o S.G. for complex life dispelled in 1600’s
o L. Pasteur, 1862, all life from life (Swannecked flask)
 Four stages:
1. Abiotic synthesis of amino acids and nucleotides
2. monomers into polymers like A.A.protein and
nucleotidesnucleic acid
3. Protobionts
1. droplets with membranes
2. maintain internal chemistry diff. from environ.
4. Origin of self-replicating molecules (RNA) make life
possible.
15.2 Describe the experiments of Dr. Stanley Miller and
their significance in understanding how life might have
first evolved on Earth.
15.3 Describe the significance of protobionts and
ribozymes in the origin of the first cells.
Abiotic Synthesis of Macromolecules
Without enzymes to catalyze synthesis reactions of monomers
into polymers, where did the large amount of EA come
from?
Formation of Protobionts
Protobionts: isolation of a collection of abiotically created
molecules within a membrane, first “cell.”
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Protobionts or Protocells:
 Allowed for the concentration of certain combinations
of molecules that interact more efficiently.
 Different environment than surroundings.
Abiotically formed lipids:
 can form small bounded droplets in water
 Act like phospholipid bilayer
 Selectively permeable membrane surface
 Swell or shrink osmotically
 With enzymes, some can carry out simple metabolic
reactions.
Self-Replicating RNA:
 Central Paradigm: DNARNAProtein
 Evolved slowly, simplecomplex
 First genes: Self-replicating RNA (assemble
spontaneously)
 First natural selection: RNA molecules that were any
better at self-assembly
 Ribozymes: RNA molecules that are enzyme-like
Major Events in the History of Life
15.4 Describe the key events in the history of life on
Earth.
Origin of Prokaryotes:
 3.5 bya2 bya
Production of O2.

 “Oxygen Revolution”
o oxidizing rather than reducing atmosphere.
o oxidized iron in crustred soil deposits
worldwide
o poisoned many prokaryotes caused
extinction
o some survived in anaerobic environments
o oxygen-binding as protection may have been first
step toward aerobic respiration
o allowed these prokaryotes to flourish
Origin of Single-celled Eukaryotes:
 2.1 bya
 Originated when small prokaryotic cells capable of aerobic
respiration or photosynthesis began living in larger cells
 Great range of unicellular forms evolved
Origin of Multicellular Eukaryotes:
 1.5 bya
 Next wave of diversification
 descendants include:
o algae
o plants
o fungi
o animals
Colonization of Land:
 Required protection from sun
o Photosynthesisoxygen
 rose to upper atmosphere to create
ozone
 protected life from DNA damaging
radiation from sun
 1 bya Probably began with floating prokaryotic/algal mats
 500 mya multicellular eukaryotes encroached on land
 Plants colonized land in company of fungi
 *Arthropods
o (most diverse and widespread)
o insects and spiders
 Tetrapods
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o
o
o
o
four-legged animals
includes humans
one-hour clock of Earth’s history:
H. sapiens appear 0.2 seconds ago
15.5 Distinguish between the relative age and the
absolute age of a fossil.
Absolute Age: Determining the age of rocks or artifacts using
radiometric dating, the rate of decay of unstable isotopes.
Relative Age: Indirect way to estimate the age of much older
fossils. K-40 (half-life = 1.3 by) used to date volcanic
rock layers. The age of fossils found above or below that
layer can be estimated relative to the dated rock.
Explain how radiometric dating is used to determine the
age of rocks and fossils and when carbon-14 and
potassium-40 are most appropriately used.
C-14 used to date relatively young fossils (75,000 ya)
K-40 used to date very old rocks (108 ya or 100’s mya)
Knowing both the half-life of a radioactive isotope and the ratio
of radioactive to stable isotope in a fossil enables us to
tell the age of the fossil.
Problems: Show your work, clearly labeled or explain
using your best writing skills.
1. Study the graph of the rate of decay of C-14. How long
does it take one half of the original amount of C-14 to
decay?
2. What is the half-life of C-14?
3. If a sample from an ancient leather hide was found to have
.25 grams of C-14 remaining and a modern sample had
1.0 gram of C-14, how old is the ancient hide?
4. If there is 1/8 of the original amount of C-14 remaining,
how many half-lives have passed?
5. The ratio between an ancient sample’s amount of C-14
and a modern analog is found to correspond to four halflives of C-14. How old is the sample?
6. A sample was found to have zero C-14 remaining. How
old is the sample? Explain.
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Mechanisms of Macroevolution
Macroevolution:
physical mechanisms:
continental drift
mass extinction
adaptive radiation
genetic mechanism: “evo-devo”
(genes that control the rate, timing and spatial pattern of
changes in an organism’s form as it develops)
15.14 Describe the process of convergent evolution.
Timeframe: Post Eukaryotic Multicellularity
Supercontinent formed and broke up three times
Continental plates move about slowly but incessantly on
molten mantel
Breakup of Pangaea
 180 mya
 Pangaea started to break apart
 causing geographic isolation of colossal proportions.
 Each continent became a separate evolutionary arena
 Laurasia and Gondwana: 135 mya
Radiation in Parallel
EXAMPLE:
Marsupial/Placental distribution
Before breakup
 Marsupials numerous in Australian area
 Placentals numerous elsewhere
After breakup,
 Australia:
o many placentals became extinct on continent of Australia
by competition with more numerous marsupials
o Marsupials filled all mammalian niches
 Elsewhere:
o Placentals out-competed marsupials elsewhere
o Placental filled all mammalian niches
Example:
Fossil Lung Fish
World-wide distribution indicates that lungfish evolved when
Pangaea was intact.
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15.9 Describe the causes, frequency, and consequences
of mass extinctions over the last 600 million years.
Mass Extinction: Global environmental changes were so
rapid and disruptive that a majority of species were swept
away in a relatively short amount of time.
Show: NOVA Science NOW, show#7: “Permian Puzzler” (3:30-18:00)

CAUSE
o
o
o
o
o
o
o
o
claimed 96% of marine animal species
Siberia, enormous volcanic eruptions
high CO2 levels
global warming
reduced temp differences between equator and
poles
slowed mixing of ocean water
reduced O2 available to marine organisms
oxygen deficit played large role in P.extinction
Cretaceous Extinction:
 CAUSE
o more than half of all marine species
o many lineages of terrestrial plants and animals
o over just 10 m.y. all dinosaurs (but bird
ancestors) gone
o Evidence: Iridium in layer of clay worldwide 1
million x higher than normal

Iridium is very rare on Earth

common in meteorites

correlates to end of Cretaceous
o hypothesis: fallout from giant meteorite

evidence: crater in Yucatan peninsula

180 km wide crater, created by 10 km
meteor

enough material to create dust cloud
that would instantly kill most animals in
N. Amer.
Consequences
 Affect biological diversity profoundly
 Can decimate a thriving and complex ecological
community
 Random events that act on species indiscriminately
 Can permanently remove species with highly
advantageous features
 Can change the course of evolution forever.
 Recovery Time?
o 5-10 my
o Permian: 100 mill.
15.10 Explain how and why adaptive radiations
occur.

How: Opening up niches due to:
o Extinction of species

dinosaurs died out

mammals radiated into previouslyfilled niches
o New territory

volcanic islands

Galapagos Finches
o Adaptations that open new niches

bilateral symmetry: predation

burrowing muscles: opened ocean bottom

stems, waxy covering: opened terrestrial

wings: opened skies

webs: capture flying prey

Why:
o
Natural selection and the struggle to survive.
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o
o
o
Utilizing a niche with less competition is adaptive.
Allows for health and high fecundity.
Exponential Growth in new niches.
Review:
Macroevolution:
physical mechanisms:
continental drift
mass extinction
adaptive radiation
genetic mechanism: “evo-devo”
(genes that control the rate, timing and spatial pattern of
changes in an organism’s form as it develops)
15.11 Explain how genes that program development
function in the evolution of life.
“evo-devo”: scientists working at the interface of
evolutionary biology and developmental biology are
studying how slight genetic changes can become
magnified into major morphological differences between
species.
Intensity of cause vs. magnitude of effect.



Changes in Spatial Pattern:
Homeotic genes:
o master control genes in development
o they determine where appendages will develop.
o Changes in such genes or in where these genes
are expressed can have a profound impact of
body form.
Example: Evol. of terrestrial vertebrates from fishes.
o Location in developing limb where homeotic gene
is expressed is initially the same between the
two.
o A second region of expression in the developing
tetrapod limb, however, produces the extra
skeletal elements that develop into foot bones.
o Changes in the expression of these genes
appear to have led to the evolution of walking
legs from the paired fins of fishes.
15.11 Define and describe examples of paedomorphosis.


Paedomorphism: retention of juvenile features of
ancestors into adulthood.
Examples:
o Axolotl keep external gills at adulthood instead of
lungs.
o Humans and chimpanzees are much more alike
as fetuses than they are as adults.
o Human adult skull is like the fetal skull: rounded
skull and small jaw make the face flat and
rounded.
o Chimpanzee brain after birth shows slow growth
while our brain continues to grow at fetal rates for
one year.
o Both skull and brain show retention of fetal traits.
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15.12 Define exaptation and describe two examples in
birds.
Gradual refinement from simpler versions having the
same basic function into intricate versions (eyes):

Simple ancestral patch of photoreceptor cells

Diverged into vertebrate eye and squid eye.

Both use same master genes that regulate eye
development.

Evolved through a series of incremental modifications
that benefited their owners at each stage.
Gradual adaptation of existing parts to new functions
(wings).
Exaptations: Structures that evolve in one context but
become co-opted for another function. A structure can
become adapted to alternative functions. Novel features can
arise gradually via a series of intermediate stages, each of
which has some function in the organism’s current context.
Examples:
Evolution of feathers from dinosaurs to birds.

First evolved as insulation

Mating displays

thermoregulation

camouflage

First flights were mere hops to pursue prey or escape
predation.

Once flight became an advantage, natural selection
would have remodeled feathers and wings to fit their
additional function.
Penguins are flightless but excellent swimmers

wings became “flippers”

reduced feathers
Phylogeny and the Tree of Life
15.14 Distinguish between homologous and analogous
structures and provide examples of each.
Homologous structures: due to common ancestry and using
“parts available.”
Analogous: When natural selection (environment) favors
similar adaptations. Creates convergent evolution.
15.14 Describe the process of convergent evolution.
see parallel evolution of marsupial and placental mammals.
15.17 Explain how molecular biology is used as a tool in
systematics.
Molecular Systematics: Comparing nucleic acids or other
molecules to infer relatedness.
See activity: “Biochemical Evidence” and its summary below.
The more recently two species have branched from a common
ancestor, the more similar their DNA sequences should be.
The longer two species have been on separate evolutionary
paths, the more their DNA is expected to have diverged.
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