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Natural Selection
A Critical Thinking Approach
Start Thinking???
(Write answers in your notes)
• Define Evolution in your own words
• How do you think evolution happens?
(What is the mechanism)
• How long do you think evolution takes???
Problem Solving
• Cheetahs are the world’s fastest land mammal.
They have the ability to run almost 70 mph in
pursuit of prey. All other big cats can only run
about 35 mph over very short distances
– Do you think the cheetah’s speed is important to its
survival? Why or why not?
– How do you think a biologist would explain the
cheetah’s speed, based on the fact that their
ancestors (and all other cats) only run 35 mph)
– Remember, you are trying to think of a way that all
cheetahs got faster over time
Georges Cuvier (1769-1832)
Georges Cuvier
• Saw org. as complete wholes, w/ each
body part fully integrated into the entire
org. No single part could be altered w/o
damaging the entire org.
• Also suggested appearance of new org. in
fossil record occurred through special
creation events following natural
catastrophes
Questions
• How do you think Cuvier would explain the
cheetah’s speed?
• Do you think Cuvier’s explanation is
scientific? Why or why not?
• How could test Cuvier’s ideas
• “Same as it ever was”
Jean-Baptiste Lamarck (17441829)
Jean-Baptiste Lamarck-part 1
•
3 basic ideas:
1. A change in the envir causes a resulting change in
the org. behavior
2. The behavior change causes the org. to use or not
use various organs
3. The added use of an organ will cause it to grow &
become more complex, the disuse of an organ will
cause it to atrophy or waste away
For Example, Lamarck thought that giraffes got longer
necks by stretching to reach food. By using all of
the muscles in the neck, their necks got longer. The
giraffes would then pass on the extra height to their
offspring, who would be born just as tall as their
parents.
“Use it or lose it”
Questions
• Do you think Lamarck’s explanation is
scientific? Why or why not?
• How could you test Lamarck’s ideas?
• How do you think Lamarck would explain
the cheetah’s speed?
• How could you test the ideas about
inheritance?
Doberman Tail Docking?
Body Builders?
War Amputees?
Charles Darwin
4 Basic Ideas:
1. There are variations w/in populations of org.
2. Variations can be passed to offspring
3. Each generation produces more offspring than
survive to adulthood
4. The org. w/ the favorable characteristics
survive better and reproduce more often, thus
transmitting their traits to the next generation
Charles Darwin 1809-1882
HMS Beagle
Questions
• How do you think Charles Darwin
explained the cheetah’s speed?
• Do you think Charles Darwin’s explanation
is scientific? Why or why not?
• How could you test Charles Darwin’s
ideas?
“NATURAL SELECTION”
Reflection
• Cheetahs are the world’s fastest land mammal.
They have the ability to run almost 70 mph in
pursuit of prey. All other big cats can only run
about 35 mph over very short distances
– Review your answer to this question: How do you
think a biologist would explain the cheetah’s speed,
based on the fact that their ancestors (and all other
cats) only run 35 mph?
– Which of the 3 evolutionary thinkers does your
explanation sound like???
Classwork
Scientist
Ideas
Scientific Y/N Hypothesis
Supported/Refuted
Cuvier
Darwin
Lamarck
Who Said This???
• “The fennic’s ears grew large b/c the heat of the
desert caused the fenic to use its ears to release
heat. The ears grew b/c of this new added use.
• After its ears grew it passed the trait for bigger
ears onto its offspring, which also used their
ears more which caused more growth & over
time the fennic’s ears became what we see
today.”
Who said this???
• The viper became wonderfully camouflaged b/c each generation of
vipers has variations in their camouflage.
• The vipers w/ the best camo are more likely to escape becoming
dinner for some predator. Also the vipers w/ the best camo are more
likely to get more food b/c they were better able to sneak up on their
prey.
• Meanwhile the poorly camo’d vipers are more likely to be eaten & to
suffer from lack of food.
• The result is that the better camo’d vipers survive better and
reproduce more often than their poorly camo’d counterparts.
• Each generation of vipers receives its genes from the survivors of
previous generations, so the collection of genes is being filtered, in a
sense, w/ the genes for poor camo being removed & genes for good
camo being maintained.
Who
said
this???
Feathered feet are an advantage for a bird in a cold climate.
•
• In the past the snowy owl pop. Had lots of variation in the amount of
feathers on their feet, but in each generation the owls w/ the most
feathers on their feet (& therefore the best insulated feet) had the
best chance of surviving the cold & enetually reproducing.
• The owls w/ less insulated feet would have difficulty in surviving the
cold and consequently reproduced less than other owls.
• Over many generations of owls, the characteristic of highly
feathered feet became prominent