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Natural Selection Scenarios
Bell Ringer
• Write your learning targets at the top of your
notebook page
• Silently complete the exit quiz from last class
Bell Ringer (10 minutes)
Review (10 minutes)
Scenario Practice (10 minutes)
Group Activity (40 minutes)
Independent Practice (10 minutes)
Exit Quiz (10 minutes)
Essential Question
• How does overproduction, inherited
variation and the struggle to survive allow for
natural selection?
“It is not the strongest of the species that
survives, nor the most intelligent that
survives. It is the one that is most adaptable
to change.”
Charles Darwin
Natural Selection
• Natural Selection: the process in nature
where the most fit organisms survives to
reproduce and pass on traits to offspring
• Natural selection leads to evolution
• There are three requirements for natural
selection to occur
1. Overproduction=organisms produce more
offspring than needed and not all offspring
will survive
– Offspring will compete for resources
2. Inherited
Variation=there are
differences among
the organisms in a
population caused by
genetic mutations
and recombination
– Some variations will
be better for survival
than others
3. Struggle to survive= organisms must compete
for resources and fight to stay alive
• Overproduction + inherited variation +
struggle to survive = differential reproductive
• Differential reproductive success=individuals
with certain traits are more likely to survive
and reproduce; those traits will be more
frequent in the population
You should be:
Natural Selection Example
• Which rabbit has a better chance of
surviving in the North Pole? Why?
You should be:
Natural Selection Example
Oh, snap, I just found
Gosh darn it, no
rabbits here.
All the brown rabbits die
Only one white rabbit dies
White rabbits have babies
Now we have ALL white rabbits!
Now assume only fat rabbits can
survive the cold
Now we have all fat white rabbits
- We can say that the rabbits evolved into fat white
- The process is called evolution.
Moth Scenario
In England, a species of moth called the peppered
moth lives on trees. Peppered moths can either look
light with gray spots or can look dark. During the
1800s, the Industrial Revolution changed the landscape
of England. New coal-powered factories spewed tons
of dirty smoke into the air, blanketing the forests with
soot. The tree trunks were darkened by the pollution.
When this happened, the light colored moth form was
easier to spot than the dark form, and as a result more
were eaten. By 1895, dark moths accounted for nearly
100% of the total population in some forests.
How is this natural selection?
Group Activity
• We will simulate natural selection of finches
on the Galapagos islands
• It is crucial that you follow ALL INSTRUCTIONS
• If you are not following instructions, you will
not participate
Sexual Selection Scenario
• Felix always felt a little awkward
with his extra-long trunk. When
he reached adulthood, he found
out that ALL the female
elephants found this once
strange trait, VERY attractive.
• Predict how this trait may
become very common in the
elephant population over
several generations.
Behavioral Selection
• Lemmings are small rodents who
reach sexual maturity a month after
birth and have large litters.
Periodically, when their populations
exceed their resources (carrying
capacity), groups of lemmings will
jump into water. This was historically
thought of as a mass suicide.
• Clearly, suicide is NOT FAVORABLE
explain this behavior as being
advantageous to the ENTIRE
lemming population?
• You and your classmates will simulate the survival of birds called
medium ground finches on Daphne Major, one of the Galápagos
Islands. This bird species has three possible variations in beak
shape: deep, cutting, and pointy. Each “bird’s” ability to acquire
food will determine whether it dies, or whether it survives.
• Medium ground finches typically feed on small, soft fruit and seeds.
The birds prefer soft seeds because they are easier to crack.
However, during periods of drought, food becomes scarce. The
birds are forced to eat more hard seeds that are difficult to break
open. Birds with deeper beaks are better able to crack open hard
seeds than birds with shallower beaks. These variations in beak
depth made it possible for some of the medium ground finches to
get enough food to survive and reproduce during long droughts.
• After simulating changes in the bird population for six generations,
you will analyze data to discover how the frequency of each beak
phenotype in the population changed over the generations
• Independent Variable: what are we
purposefully manipulating in the activity?
• Dependent Variable: what are we going to
measure in the activity?
• Constants: what will be kept the same?
• As a group, form an “If…then…because…”
hypothesis about what will happen in the
• For example:
“If we test (independent variable) then we will
see (dependent variable) because…”
• For each round, use your beak and to pick up as
much food as you can and put it your “nest” (plastic
• You need to collect 10 pieces of food by the time the
timer runs out to stay alive.
• You may only pick up ONE piece at a time.
• If you collect 15 or more, you “reproduce” (get
another of your beak type from Mrs. Franklin).
Practice Round
• Practice gathering “seeds” for one minute
Data Table
Independent Practice
Big Idea: Bacterial Resistance
Exit Quiz
• Finish the group activity worksheet!