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Chapter 19:
MacroEvolution and the Evidence
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2006-2007
Macro-evolution
 Looking at the big picture.
 Looking at what drives the diversity
and unity of life
cells
DNA
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One form of evidence in the unity of life…..
Anatomical evidence
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Science sees structural similarities as evidence that
organisms evolved from a common ancestor.
Homologous
parts are similar
in structure, but
may be very
different in
specific function.
Structural features with a common evolutionary origin
are called homologous structures.
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The body parts of organisms that do not have a close
evolutionary origin but are similar in function are called
analogous structures.
Analogous parts
are very different in
structure, but
perform similar
functions.
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Vestigial organs
Thesewhales
are
Why would
remnants
of
have pelvis
& leg bones
ifstructures
they were that
alwayswere
sea functional
creatures? in
ancestral species
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These are structures that used to have a
function, but no longer do….therefore
suggesting evolution based on new behaviors
Video clip
or environments
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Embryology is the study of organisms in embryonic
stages.
The embryo is one of the earliest stages of growth and
development of both plants and animals.
The shared
features in the
embryos
suggests
evolution
from a distant
common
ancestor.
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Shared Common Features:
• a tail posterior to the anus
• spinal cord
• muscles arranged in bundles
• cartilage dorsal notochord (becomes the vertebral column)
• Pharyngeal gill slits
Pharyngeal
pouches
Pharyngeal
pouches
Tail
Fish
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Tail
Reptile
Bird
Mammal
BIOCHEMISTRY
All living things have A,T,C,G in their DNA and use
the same codon chart to code for the same amino
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acids.
The biochemistry (DNA) of a bat is much
closer to that of a whale, than that of a
bird.
Why?
The same technology used to determine
paternity can be done to determine
shared ancestry.
Because bats and whales are
mammals!
Therefore, more closely
related…..
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Bat
Whale
Bird
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Another form of evidence that evolution occurs….
Fossil record
550
500
Body size (kg)
450
Equus
400
350
300
250
Merychippus
200
150
Mesohippus
Hyracotherium
100
50
Nannippus
60 55 50 45 40 35 30 25 20 15 10 5 0
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Millions of years ago
Fossils are usually formed when an organism is covered by
sediments that then harden into sandstone, slate, mudstone or flint.
Most of the time, organisms die in locations
that are not conducive to fossilization.
Most organisms do not fossilize and
those that do are usually destroyed by
geological processes or they never
surface for examination.
We have only discovered about 250,000
fossilized species. This tells us that there
are many gaps in the fossil record.
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 Fossils are evidence of organisms that lived long ago
that are preserved in Earth’s rocks.
TYPES OF FOSSILS
Fossils Types
Formation
A trace fossil is any indirect evidence
Trace fossils
Casts
left by an animal and may include a
footprint, a trail, or a burrow.
When minerals in rocks fill a space
left by a decayed organism, they make
a replica, or cast, of the organism.
A mold forms when an organism is
Molds
Petrified
fossils
Amber-Preserved
or
frozen fossils
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buried in sediment and then decays,
leaving an empty space.
Petrified-minerals sometimes penetrate
and replace the hard parts of an organism
At times, an entire organism was
quickly trapped in ice or tree sap that
hardened into amber.
 Paleontologists, scientists who study ancient life, are
like detectives who use fossils to understand events
that happened long ago.
 They use fossils to determine the kinds of
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organisms that lived during the past and
sometimes to learn about their behavior.
• Relative Dating Techniques
Law of superposition
(Nicolaus Steno)
You cannot use this
technique to get the
actual
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Most Complex
Most Primitive
The first fossilized fish appear buried below
the first fossilized amphibians which appear
below the first fossilized reptiles which appear
below the first fossilized birds and mammals.
This is consistent with the Darwinian model of
origins which says that birds and mammals
evolved from earlier reptile ancestors, which
evolved from amphibian ancestors which
evolved from fish ancestors.
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Fossil evidence for evolution concerns
transitional fossils.
Transitional fossils are fossils which are
thought to document the evolutionary
change, or transition, of one species
into another.
The Mesohippus, Merychippus, and
Pliohippus are all thought to be
transitional fossils, documenting the
evolution of the Eohippus into the
modern horse.
Perhaps one of the most famous “transitional
fossils” of all time was the archaeopteryx
[ahr-kee-op-tuh-riks], which shows evidence of
transitioning between a reptile and a bird.
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Evolution of birds
 Archaeopteryx


lived about 150 mya
links reptiles & birds
Smithsonian Museum,
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Washington,
DC
Evolution of land animals
 2006 Fossil Discovery
“Tiktaalik”
 “missing link” from sea to land animals

 from swimming (0 legs) to walking (4 legs)
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Evolution of
marine mammals
Land Mammal
?
?
?
?
But then,
they actually
found my fossil!
At first,
I was just
a joke!
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Biology
Aquatic Mammal
• Radiometric Dating Techniques
To find the specific age of rocks, scientists use
radiometric dating.
By using the radioactive isotopes present in rocks, and understanding the rates
at which these isotopes decay, scientists can determine approximate age of the
rocks.
Atoms of the same element with differing atomic weights can be naturally found
in the environment, and are called isotopes.
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Radioactive isotopes are atoms with unstable nuclei that
break down, or decay, over time, giving off radiation. The
isotope is eventually changed into, or replaced by another
element over time.
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As specific atoms decay they emit radiation and lose
electrons, which causes them to turn into a different
element.
So- these atoms change from one thing into something else
over time- and they do this at a constant rate.
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 If you know what the unstable atom is (Carbon 14)
and you know what it turns into as it decays
(Nitrogen 14).
 And you know the rate at which the unstable atom
decays/turns into something else
It takes 5,730 years for ½ of Carbon 14 to
turn into Nitrogen 14
 You can measure the amount of the unstable parent
atom in the rock….and compare that to the amount
of the new atom
 This will tell you the age of the sample rock.
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 The half-life of a radioactive atom is the time it takes
for half of that atom in a sample to decay and turn into
another element.
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• The element potassium-40
decays to argon-40 and has a halflife of approximately 1.25 billion
years
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• The element carbon-14 decays
more rapidly into Nitrogen-14, and
has a half-life of only 5,730 years.
Because Carbon 14 has such a short half-life, it can only
be used to date things that died recently in geologic
history (under 70,000 years ago).
• You can only date organic remains using carbon 14
If you need to date rocky
material from farther back in
our geologic past, you must
use another method, such as
Potassium/Argon, which has a
much longer half-life.
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Most radioactive isotopes have rapid rates of
decay (that is, short half-lives) and lose their
radioactivity within a few days or years.
Some isotopes, however, decay slowly, and several of these
are used as geologic clocks. The parent isotopes and
corresponding daughter products most commonly used to
determine the ages of ancient rocks are listed below:
Parent Isotope
Stable Daughter
Product
Uranium-238
Lead-206
4.5 billion years
Uranium-235
Lead-207
704 million years
Thorium-232
Lead-208
14.0 billion years
Rubidium-87
Strontium-87
48.8 billion years
Potassium-40
Argon-40
1.25 billion years
Samarium-147
Neodymium-143
106 billion years
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Currently Accepted
Half-Life Values
256 14C atoms
How many carbon-14
atoms and how many
nitrogen-14 atoms
will this rock have in
5,730 yrs.
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After 5730
years
or 1 half-life
128 14C and
128 14N atoms
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After 11,460 yrs
or 2 half-lives
64 14C and
192 14N atoms
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After 17,190 yrs
or 3 half-lives
32 14C and
224 14N atoms
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After 22,920 yrs
or 4 half-lives
16 14C and
240 14N atoms
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After 28,650 yrs
or 5 half-lives
8 14C and
248 14N atoms
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After 34,380 yrs
or 6 half-lives
4 14C and
252 14N atoms
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After 40,110 yrs
or 7 half-lives
2 14C and
254 14N atoms
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