Transcript Evidence of Evolution

Evidence of
Evolution
In this program, you will learn more about the
evidence that Charles Darwin and scientists since then
have found that shows life has evolved.
Courtesy of Tom Wanamaker, Appleton East High School, Appleton, WI
At several points in the program:
• You will be asked questions to check
your understanding of the concepts.
• To respond, click the correct answer.
• Don’t worry if you get an answer wrong
-- you will still learn something.
Next
Here’s the first question:
Q: Why is it called the Theory of Evolution?
1. It has been thoroughly tested many times
by many people and has gained widespread
acceptance.
2. It has not yet been proven well enough to
satisfy most people.
Correct!
• The term “theory” has multiple meanings.
– People commonly use the word to mean a wild guess.
– In science, though, it means almost the exact opposite!
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Actually, A is correct.
• Don’t feel bad, though -- the term “theory” has multiple
meanings.
• People commonly use it to mean a wild guess.
• In science, though, it has almost the exact opposite meaning!
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Scientific theories are testable hypotheses
that explain observable data.
•
Atomic Theory, Germ Theory, the Cell Theory, the Theory of Relativity,
Plate Tectonics and Gravitational Theory are all examples of accepted
scientific theories.
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Like evolution, each of these theories is the simplest explanation that
fits with the available data. Each has been repeatedly tested by
experts in the field and found to be acceptable.
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People today don’t question the accuracy of these theories, but new
data may force scientists to change them or even throw out them out.
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For this reason, scientists prefer not to say that a theory is proven to
be a fact. (Facts are the observations used to support theories.)
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Testing a Theory is a Rough Business
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For a long time, people accepted the Geocentric Theory. Their observations
seemed to show that the sun, stars, and planets revolved around the Earth.
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Careful observations made by later scientists didn’t fit this model, and it was
eventually scrapped in favor of the Heliocentric Theory.
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This is the Home Page
Fossil
Record
Fossil Record is a
good place to start
Convergent
Evolution
Comparative
Anatomy
Evidence of
Evolution
Molecular
Comparisons
Embryological
Development
From the Home Page, you can
investigate several lines of
evidence that support the
Theory of Evolution.
Click any box to enter that area.
Vestigial
Structures
Fossil
Record
Convergent
Evolution
Comparative
Anatomy
Evidence of
Evolution
Molecular
Comparisons
Embryological
Development
Vestigial
Structures
When you think fossil, what
comes to mind?
• I know what you were thinking…
Fossil Record
• Fossil Facts:
– A fossil is any part or trace of a once-living organism.
• It may be bones, but there are other types of fossils.
– Click one of the items below to learn more about the
different types of fossils.
Trace Fossils
Imprints
Amber
Molds/Castings
Petrified Wood
Fossilized Bones
Frozen Organisms
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Trace fossils include burrows,
tracks, even fossilized poop!
Fossil burrows
Dinosaur tracks
Dinosaur & Fish Poop
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Amber
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Amber is fossilized tree sap. It often traps pollen, insects and
other small animals.
Insects trapped in
amber.
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Petrified Wood
• When wood is buried in ash or sandy sediments, silica can
form within the wood structure, eventually replacing the
organic material.
These petrified logs are found at
Petrified Forest National Park in Arizona.
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Molds/Castings
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Molds and castings form when the hard shell or exoskeleton of
an organism is buried in sediment and the sediment hardens.
The sediment hardens around the body, then the body dissolves or
decomposes, leaving a void or mold.
The mold can fill with minerals to form a cast in the shape of the mold.
Casting of a fossil trilobite
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Frozen Organisms
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In some places, animals and plants get trapped in snow and
are preserved for thousands of years.
This obviously happens only in cold mountainous and polar areas.
Above - Otzi, the famous “Ice Man”
found frozen in the Italian Alps
Left - Dima, a baby mammoth found
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preserved in the Siberian permafrost
by Russian miners.
Imprint Fossils
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When plants and animals fall in fine sediments, their bodies
can sometimes leave an imprint that shows up when the
resulting rock layers are split apart.
Clockwise from left - The
imprints of feathers can be
seen in the Archaeopteryx
fossil. A dragonfly imprint in
the same fine sediment bed.
The delicate imprint of an
extinct fern’s frond.
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Fossil Bones
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Bones and teeth of vertebrates are resistant enough to remain
intact when the rest of the body has decayed.
Dinosaur skeletons are among the most spectacular fossils ever found.
A 12,000 year old mammoth skeleton
Sue, the largest, most complete T. rex fossil ever
found. It resides at the Field Museum in Chicago.
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If evolution had not occurred, click the statement
below that should be true about the fossil record.
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Different rock layers should contain different fossil species.
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Younger (shallower) rock layers should contain fossils that look more
like modern organisms.
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Most rock layers should contain fossils of species that are not alive
today.
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Every rock layer should contain fossils that look exactly the same.
That’s right.
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If every species had always been present in its current form, then we
should be able to find fossils of all modern species -- from bacteria to
humans -- in every layer of rock.
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It wouldn’t matter how deep you dig -- if modern species were living
from the very beginning of earth’s history, then some fossil evidence
should exist even in the oldest rocks. It doesn’t.
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By itself, the fossil record provides strong evidence that evolution has
occurred.
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Actually, this statement should be correct
if evolution has occurred.
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Think about what it means for things to evolve.
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Evolution refers to the change that happens in species over time.
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Go back and try to pick out the statement that should be true if things
NEVER changed.
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Conclusion:
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The fossil record shows a progression from simple life forms to
more complex, modern-looking forms.
•
The only logical explanation is that life has evolved from a single life
form into the diversity we see here today.
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Convergent Evolution
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Convergent evolution refers to the tendency of different
species to evolve similar adaptations in different places
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Convergence happens because these different species face
similar selective pressures as they struggle to survive and pass
on their genes.
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There is no guarantee that similar selective pressures will lead to
convergence, since all adaptations are due to mutations and/or new
gene combinations.
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Click the next button to see some examples of convergent evolution.
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Examples of Convergence:
(Click on the examples below for more information.)
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Whales and Fish
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Marsupials and Placental Mammals
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Counter-shading coloration and other forms of camouflage
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Mimicry
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Hedgehogs and Porcupines
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Beaver and Capybara
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Whales and Fish
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The ancestors of fish evolved to swim in the water, which supports the
body’s weight, but is much more dense than air.
The ancestors of whales were 4-legged mammals living on land.
As ancestral whales evolved to live and move in the water, they faced
the same selective pressures that favor fins and a streamlined shape.
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Marsupials and Placentals
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The first mammals to evolve laid eggs, like their reptilian ancestors.
(Only two species of egg-laying mammals are alive today.)
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Marsupials, pouched mammals, give birth to underdeveloped young,
who then complete development in their mother’s pouch. Nearly all of
them are found in Australia/New Zealand.
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Placental mammals keep their young inside of the mother’s uterus,
connected to her through the placenta. Most of the world’s mammals
are placental.
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Still, because the same types of selective pressures exist in Australia
and different habitats in other parts of the world, we would expect
some convergence to evolve.
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Examples of Marsupials/Placentals:
Marsupial and
placental species may
look the same on the
outside and occupy
similar niches in their
environment, but all of
the placental mammals
are more closely
related to each other
than to any marsupial,
and vice versa.
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Marsupials
Placentals
Camouflage and Coloration
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There is a strong selective pressure for most animals to blend in with
their surroundings. It helps them hide from predators and their prey.
This giraffe and grasshopper are not closely related animals, but the
same selective pressure to blend in has led to similar color and markings.
Octopus video
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Mimicry
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Sometimes, it is good to stand out. Dangerous animals like poison
arrow frogs, bees, and nasty-tasting insects have markings that warn
potential predators. Bright, high-contrast patterns are universal signals
to stay away.
“Leave us alone!”
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Sometimes, it pays just to look tough. See if you can
pick out the wannabes in the examples below.
Click on the dangerous insects.
or…
or…
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The monarch butterfly on the left is poisonous and will
make a bird that eats it sick. The viceroy on the right is
harmless, but the birds that have made the mistake of
eating a monarch won’t touch it.
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The yellow jacket on the right can afford to be aggressive because
it has a stinger to back up its behavior. The hoverfly on the left is
very tame. It flies from flower to flower eating nectar, confident
that its colors will protect it from any nosy predators.
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Hedgehog & Porcupine
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Hedgehogs are insectivores and porcupines are rodents, but both are
mammals that defend themselves with spiny hairs.
Each had ancestors that experienced mutations that produced stiff,
spiky hairs. It turns out that these mutants were successful and
survived attacks by predators.
As a result, they were able to reproduce and pass on these traits to the
next generation.
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Beaver and Capybara
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Beaver and capybara are large, distantly related rodents – the beaver
lives in North America and the Capybara in South America.
They both evolved similar traits living in similar marshy environments
and engaging in similar ecological roles.
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Comparative Anatomy
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Humans, cats, whales and bats are all mammals, but they engage in
totally different lifestyles. On the outside, their bodies appear to be
perfectly designed to perform different functions.
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Comparative Anatomy
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If all of these mammals evolved from the same ancestral mammal, we would
expect to see underlying anatomical similarities despite the obvious differences.
Underneath the skin, all of these animals share the same skeletal anatomy –
one that was inherited from their common ancestor.
The appearance of design is an illusion produced by the effects of natural
selection.
Home
Vestigial Structures
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Mutations are always producing new body forms each generation.
Sometimes, environmental changes and mutations combine to provide
new opportunities for species.
As species evolve to fill different niches in their changing world, we
would expect their bodies to change over many generations.
Vestigial structures are body parts that are reduced in size and
function. Mutations that reduce the size of such structures are not
harmful and may actually be of a benefit to the individuals that inherit
them.
Click on one of the examples below to learn more.
Fossil whale legs
Human coccyx
Snake leg spurs
Reduced eyes
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Fossil Whale Legs
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Whales are mammals that have no hind legs.
They are thought to have evolved from 4-legged land animals that lived over 50
million years ago.
Paleontologists expected to find whale ancestors that showed reduced and
vestigial legs by looking in sediments that were between 50 and 30 million years
old. Sure enough, they did. Some examples of this transition are shown below.
Ambulocetus
Pakicetus
Basilosaurus
42 million years ago
40 million years ago
49 million years ago
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Coccyx in Humans & Apes
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Humans and other hominiod apes evolved from primates that had an
external tail.
In our hominoid ancestor, it was reduced to a small coccyx or tailbone
that is not visible on the outside of the body.
The coccyx or tailbone
is visible in the chimp
pelvis on the left and
the human pelvis on
the right.
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Snake Leg Spurs
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Snakes evolved from four-legged lizards, but mutations that reduced or
eliminated their legs provided new opportunities for their ancestors.
The genes that produce legs are still there, however, and in some
species of snakes, there are actually vestigial legs.
Leg spurs are visible on the
underside of this female ball
python.
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Reduced Eyes in Cave Dwellers
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Mutations that reduce or eliminate eyes in species that dwell in caves
are not harmful, and may benefit the individuals that experience them.
Many different cave species show these same mutations.
Several examples of eyeless cave-dwelling animals
The fish Astyanax comes in two varieties –
the surface-dwelling varitey is on the left,
the eyeless cave fish is on the right. The
mutation that eliminates eyes also gives
the fish a larger jaw and more taste buds.
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Comparative Embryology
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Species that reproduce sexually start out as a fertilized egg – a
single cell. All fertilized eggs are basically the same. Early
embryos are similar and then they start to differ later in
development.
As the egg divides again and again, master control genes activate to
establish the basic body plan of the organism.
Although these genes were first discovered in fruit flies, they have
been found in all animals.
Other genes that control embryonic development take each species
from the same basic starting point down their own path of
development.
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Home
Comparison of Proteins & DNA
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Darwin didn’t have access to knowledge about DNA and genetics like
we do today, but he did understand that individuals passed down their
traits to their offspring.
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If genetic changes (mutations) have led to the changes that
form new species, then we should expect species that share a
recent common ancestor to have fewer differences.
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Species that share a more distant common ancestor should have more
genetic differences because there has been more time for random
mutations to build up.
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Comparison of Proteins & DNA
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Chimpanzees are humans’ closest living relative – in other
words, we share a more recent ancestor with them than any other
living species. Our genes are 96% identical.
The humans and chimps last shared an ancestor with the gorillas at an
earlier time. Human and chimp DNA is 97.7% identical to a gorilla’s.
Human, chimp, and gorilla genes are 96.3% identical to orangutan
genes.
Orangutan
Gorilla
Human
Chimpanzee
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Comparison of Proteins & DNA
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Even when one considers a species as distantly related to
animals as a yeast, there are still similarities to be found.
Half of the genes in a yeast are also found in humans.
Experiments have shown that mutant yeast can be fixed by inserting
the human version of a gene to replace their defective gene.
These genes have been inherited from our common ancestor, which
lived well over half a billion years ago.
Yeast
Primates
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Comparison of Proteins & DNA
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Cat: 90%
Cow: 80%
Mouse: 75%
Fruit Fly: 60%
Banana: 50%
Banana
Fruit Fly
Mouse
Cow
Cat
Primates
Yeast
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