Unit2: Life Over Time
Chapter 6: Evolution of Living Things
6.1 Earth has been home to living things for about 3.8 billion
years
6.2 Species change over time
6.3 Environmental changes can affect populations
6.4 Many types of evidence support evolution
6.3 Many types of evidence support
evolution
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Before, you learned:
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Natural selection explains how living things evolve
New species develop from earlier species
The survival of a species depends on how well it adapts to
change
Now, you will learn
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How scientists develop theories
About the evidence Darwin used to support evolution
About additional evidence most scientists use today
http://www.pbs.org/wgbh/evolution/library
/11/2/e_s_3.html
There’s a dragon in my garage
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by Carl Sagan
"A fire-breathing dragon lives in my garage"
"Show me," you say. I lead you to my garage.You look inside and see a
ladder, empty paint cans, an old tricycle — but no dragon.
"Where’s the dragon?" you ask.
"Oh, she’s right here," I reply, waving vaguely. "I neglected to mention that
she’s an invisible dragon."
You propose spreading flour on the floor of the garage to capture the
dragon’s footprints.
"Good idea," I say, "but this dragon floats in the air."
Then you’ll use an infrared sensor to detect the invisible fire.
"Good idea, but the invisible fire is also heatless."
You’ll spray-paint the dragon and make her visible.
"Good idea, but she’s an incorporeal dragon and the paint won’t stick." And
so on. I counter every physical test you propose with a special explanation
of why it won’t work.
Now, what’s the difference between an invisible, incorporeal, floating dragon
who spits heatless fire and no dragon at all?
Observations
provide evidence
for theories
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Observations provided Darwin with information he used to
describe his ideas about evolution
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The ideas were already there (de Lemarck), but the observations –
evidence – were not
Took Darwin more than 20 years after the Beagle voyage for the
publication of his theory on natural selection
Scientific Theory: a statement based on observation and
experiment
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With continued observation and experiment, the theory may become
widely accepted
Can be used to explain AND predict natural phenomena
Theories can change as new evidence is discovered
Fossil evidence supports evolution
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Darwin collected specimens of fossils on his
trip
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Noticed that species from the past were very
similar to those of Darwin’s time
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Extinct Glyptodon ~ C./S. America Armadillo
Geographic information about fossils
provides evidence that two species with
a common ancestor can develop differently
in different locations
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Ancestor: early form of an organism from which
later forms develop
*** “common ancestors” are important to the theory of
natural selection and the evidence that supports the
theory
-ex: comparing modern plants and modern algae to
fossils of algae = share a common ancestor
Biological evidence supports evolution
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Scientist are still returning to the Galapagos to follow and record
evolutionary changes as they are unfolding, further investigating Darwin’s
work
Similarities in structure:
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Look at physical structures in different adult organisms
Biological Evidence – Similarities in
Structure
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Vestigial organs: physical structures that were fully developed and functional
in an earlier group of organisms, but are reduced and unused in later
species
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Whales still have a leg bone that is vestigial (whales are mammals that “went
back to the water”), snakes have leg-like structures, our tailbone and appendix
Help to see how modern organisms are related to ancestors that had similar
structures
Biological Evidence – Similar (homologous)
structures with different functions
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Different species may share
similar structures, which may
be used differently
One long bone goes from
shoulder to wrist
- forelimb (like book: lizard,
bat, manatee)
The similarity in structure indicates that these organisms shared a common ancestor
The process of natural selection caused the variations in form and function
The organisms lived in different environments: different pressures
 Land, water, terrain, climate, predators, food supply, etc
Side Note:
Different
structures,
same function!
Biological Evidence – Similarities in
Development
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As far back as the 1700s
scientists were
fascinated by the
similarities of animals in
their early stages of life
As they developed, they
became less and less
alike
A rabbit does not look
like a chicken, but their
embryos do (conception
 fetus)
Side note (not on test!): homologous structures vs analogous structures
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For analogous structures, they are unrelated through evolution, yet serve similar functions
(similar structure are related through evolution yet serve different functions)
The wing of a bird and the wing of a bat are
classified as being analogous structures
since their structures are unrelated.
•Such homology suggests “descent with modification” from a common ancestor: the reason the
forelimbs of these organisms contain the same bones is because they all evolved from a common
ancestor that had these bones.
•Scientists can follow changes in homologous structures through time utilizing the fossil record:
allows biologists to “visualize” evolutionary changes over time.
•A comparison of homologous bones allows scientists to assess the possible evolution of flight