Download Word Splash AP Lesson #60

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AP Lesson #60
EQ: What is natural selection?
What about Darwin’s Finches?
• He thought they were
all different kinds of
birds
• Darwin was amazed to
find out:
Large
Ground
Finch?
Finch
Small
Ground
Sparrow?
Finch
Woodpecker?
Warbler
Finch
Warbler?
Veg.
Tree Finch
– All 14 species of birds
were finches…
• But there is only one
species of finch on the
mainland!
• How did one species
of finches become so
many different
1
Large Ground
Finch
Small Ground
Finch
Descendant
species
Ancestral
species
Common
Ancestor
Warbler Finch
Veg. Tree Finch
Is there a correlation between beak type and food?
Seed
eaters
Flower
eaters
Insect
eaters
Adaptive radiation
So what did Darwin’s conclude?
• small populations of original South American
finches landed on islands
– variation in beaks enabled individuals to gather food
successfully in the different environments
• over many generations, the populations of
finches changed anatomically & behaviorally
– accumulation of advantageous traits in population
– emergence of different species
2
What does this data mean?
• Differences in beaks
allowed some finches
to…
– successfully compete
– successfully feed
– successfully reproduce
• pass successful traits
onto their offspring
• Adaptations enhance
their survival and
reproduction
More observations… Correlation of species to
food source
Many islands also show
distinct local variations in
tortoise morphology…
3
What were Darwin’s basic observations?
• Observation #1: Members
of a population often vary
greatly in their traits
• Observation #2: Traits are
inherited from parents to
offspring
ME
• Observation #3: All
species are capable of
producing more
offspring than the
environment can
support
• Observation #4:
Owing to lack of food
or other resources,
many of these
offspring do not
survive
What did Darwin’s observations tell him?
• Inference #1:
– Individuals whose
inherited traits give them
a higher probability of
surviving and
reproducing in a given
environment tend to
leave more offspring
than other individuals
• Inference #2:
– This unequal ability of
individuals to survive
and reproduce will lead
to the accumulation of
favorable traits in the
population over
generations
4
What is Darwin’s Ideas of Natural Selection?
• Natural selection
– Variation exists in populations
– Over-production of offspring
• more offspring than the environment can support
– Competition
• for food, mates, nesting sites, escape predators
– Differential survival
• successful traits = adaptations
– Differential reproduction
• adaptations become more
common in population
What does it all mean?
• Natural selection does not
create new traits
– edits or selects for traits
already present in the
population
• Local environment
determines which traits will
be selected for or selected
against in any specific
population
Summarizing Strategy
• Explain how Darwin’s ideas
of natural selection can
explain the insects in the
pictures on the right.
5
Assessment
• HW: Chapter 22 Wkst
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