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Unit B: Section 1.3
There’s a dragon in my
garage
 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
 Observations provided Darwin with information he used to describe
his ideas about evolution
 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
 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
 Darwin collected specimens of fossils on his trip
 Noticed that species from the past were very
similar to those of Darwin’s time
 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
 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
 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:
 Look at physical structures in different adult organisms
Biological Evidence – Similarities in
Structure
 Vestigial organs: physical structures that were fully developed and functional in
an earlier group of organisms, but are reduced and unused in later species
 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
 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)


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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
structure,
same
function!
Biological Evidence – Similarities
in Development
 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)