Natural SelectionNatural Selection

A Critical Thinking ApproachA Critical Thinking Approach

Start Thinking???Start Thinking???(Write answers in your notes)(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 SolvingProblem 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 (1769-1832)

Georges CuvierGeorges 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

QuestionsQuestions

• 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 (1744-Jean-Baptiste Lamarck (1744-1829) 1829)

Jean-Baptiste Lamarck-part 1Jean-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”

QuestionsQuestions

• 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?Doberman Tail Docking?Body Builders?Body Builders?War Amputees?War Amputees?

Charles DarwinCharles 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 Charles Darwin 1809-1882

HMS BeagleHMS Beagle

QuestionsQuestions

• 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”

ReflectionReflection

• 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???

ClassworkClassworkScientist Ideas Scientific Y/N Hypothesis

Supported/Refuted

Cuvier

Darwin

Lamarck

Who Said This???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???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???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