Name _________________ # ____
Mrs. Geithner-Marron Bio 200
Natural Selection: For the Birds
Period _______
Date ________
Purpose: To discover the advantages and disadvantages of phenotype variation, by
simulating natural selection (and subsequent death or reproduction) in a population of birds
(with different types of beaks) that are competing for a common food source.
Background: Charles Darwin was amazed by the variation in the characteristics of plants
and animals he encountered on his journey (especially the finches on the Galapagos
Islands). In any habitat, resources such as food are limited and the types of resources
(foods) available may vary, so there will be a “struggle to survive” (competition).
Individuals that have beneficial variations that enable them to take advantage of available
resources (foods) will be more likely to survive (“survival of the fittest”). These
beneficial variations that increase an organism’s chance of survival are also known as
“adaptations”. Those individuals with the most helpful adaptations will be the most likely
to live long enough to successfully reproduce and pass on their genes to the next
generations (natural selection). This process causes changes in the allele frequencies (%
of a gene) in a gene pool over time and ensures that beneficial adaptations will continue in
future generations (making up a larger percentage of the population), while
disadvantageous characteristics will decrease or “die out”. This change in populations (and
species), over time, is evolution; natural selection is the mechanism (or driving force)
behind evolution.
Name _________________ # ____
Mrs. Geithner-Marron Bio 200
Natural Selection: For the Birds
Period _______
Date ________
Materials:
 tray (or just mark off an area on the table using tape)
 timer (1 per group)
 “food” (kidney beans or similar—approximately ½ -1 bag per group)
 “stomach” (small bathroom cups or similar—1 per student)
 “beaks” (Have at least as many of each type as there are students in the class.)
o Examples: dropper, straw, toothpick, drink stirrer, spoon, popsicle stick, tweezers, tongs,
clothes pins, test tube clamp, (safety) scissors
 containers to hold “beaks” (optional)
Procedure:
1. Obtain “beaks”.
a. At the beginning, each person should have a different beak phenotype.
b. Fill in the name of each “beak” phenotype on both table 1 and table 2.
c. Fill in the number of individuals with each “beak” phenotype for the parent/starting
generation (generation 0) on table 1 ONLY.
2. Hypothesize: Which “beak” phenotype do you think will be “naturally selected” for in
this simulation. Explain your reasoning…
_________________________________________________________________
_______________________________________________________________
3. Spread “food” evenly over the feeding area. (Tray/marked off area on table.)
4. Place 1 hand behind your back & keep one foot on the floor. (NO pushing, hitting, etc.)
Name _________________ # ____
Mrs. Geithner-Marron Bio 200
Natural Selection: For the Birds
Period _______
Date ________
5. Everyone will have 30 seconds to obtain “food” from the feeding area using only their
“beaks” (in the way that was shown) and place the seeds into their “stomach”.
a. If the “food” falls outside the feeding area before it is placed in the “stomach”,
that piece of “food” is lost and cannot be “eaten”.
b. If the “food” falls in the feeding area, it can still be “eaten”.
c. “Food” can be “stolen” from another “bird” ONLY IN the FEEDING AREA.
d. Any “food” that is not in the “stomach” when time is called does not count.
6. At the end of the round, count & record the (average) number of pieces of food “eaten”
by each beak type AND record it on table 2 (under that generation).
7. Return the “food” to the “feeding” area.
8. To determine which “beak” phenotypes will be represented in the next generation:
a. The “bird” that “ate” the least will not survive & gives back his/her beak.
i. He/she should then take the same beak as the person who “at the most” (since
that bird was able to successfully reproduce).
b. Fill in the NEW number of individuals with each “beak” phenotype for the upcoming
“offspring” generation (1, 2, etc.) on table 1.
9. Repeat steps 3-8 five (5) more times, thus accumulating six generations of data (parent
and offspring generations 1-5).
Name _________________ # ____
Mrs. Geithner-Marron Bio 200
Natural Selection: For the Birds
Period _______
Date ________
This page intentionally left blank.
Hand in only pages 5-10. (Keep pages 1-4.)
Name _________________ # ____
Mrs. Geithner-Marron Bio 200
Natural Selection: For the Birds
Period _______
Date ________
Table 1: Number of Individuals with Each “Beak” Phenotype in Population
Generation/
Parents
Offspring
Offspring
Offspring
Offspring
Offspring
generation 1
generation 2
generation 3
generation 4
generation 5
# of
# of
# of
# of
# of
# of
Individuals
Individuals
Individuals
Individuals
Individuals
Individuals
(with “beak”
(with “beak”
(with “beak”
(with “beak”
(with “beak”
(with “beak”
phenotype)
phenotype)
phenotype)
phenotype)
phenotype)
phenotype)
# of beaks → generation 0
Beak
Phenotype ↓
Beak 1
__________
Beak 2
__________
Beak 3
__________
Beak 4
__________
Beak 5
__________
Beak 6
__________
Beak 7
__________
Beak 8
__________
Beak 9
__________
Beak 10
__________
Name _________________ # ____
Mrs. Geithner-Marron Bio 200
Natural Selection: For the Birds
Period _______
Date ________
Table 2: Number of Seeds Eaten by Each “Beak” Phenotype per Generation
Offspring
Offspring
Offspring
Offspring
Offspring
amount eaten → generation 0
generation 1
generation 2
generation 3
generation 4
generation 5
Average #
Average #
Average #
Average #
Average #
Average #
of seeds
of seeds
of seeds
of seeds
of seeds
of seeds
Eaten
Eaten
Eaten
Eaten
Eaten
Eaten
Generation/
↓ Beak
Phenotype
Beak 1
___________
Beak 2
___________
Beak 3
___________
Beak 4
___________
Beak 5
___________
Beak 6
___________
Beak 7
___________
Beak 8
__________
Beak 9
__________
Beak 10
__________
Parents
Name _________________ # ____
Mrs. Geithner-Marron Bio 200
Natural Selection: For the Birds
Period _______
Date ________
Data Analysis:
1. Graph the number of individuals with each “beak” phenotype over time (for each generation).
Use a different line for each “beak” phenotype.
a. What is the independent variable? _________________________________________
i. On which axis should this variable be plotted? ______________________________
b. What is the dependent variable? ___________________________________________
i. On which axis should this variable be plotted? ______________________________
(Y-axis) ____________________________________
(title) ___________________________________________________________
(X-axis label) ________________________________________________________
Name _________________ # ____
Mrs. Geithner-Marron Bio 200
Natural Selection: For the Birds
Period _______
Date ________
2. Graph the average number of seeds eaten over time (for each generation). Use a different line
for each “beak” phenotype.
a. What is the independent variable? _________________________________________
i. On which axis should this variable be plotted? ______________________________
b. What is the dependent variable? ___________________________________________
i. On which axis should this variable be plotted? ______________________________
(Y-axis) ____________________________________
(title) ___________________________________________________________
(X-axis label) ________________________________________________________
Name _________________ # ____
Mrs. Geithner-Marron Bio 200
Natural Selection: For the Birds
Period _______
Date ________
Discussion:
1. What type of "food" was available to the birds in this simulation? ____________________
2. Which “beak” phenotype was best adapted for the type of “food” that was available (in our
simulation)? Explain your reasoning. ____________________________________________
_______________________________________________________________________
_______________________________________________________________________
3. Which “beak” phenotype was least adapted for the type of “food” that was available (in our
simulation)? Explain your reasoning. ____________________________________________
_______________________________________________________________________
_______________________________________________________________________
4. Restate your hypothesis from page 2. __________________________________________
_______________________________________________________________________
_______________________________________________________________________
5. Did this simulation (and your answers to questions 2 and 3) support or refute your hypothesis.
Explain your reasoning. _____________________________________________________
_______________________________________________________________________
_______________________________________________________________________
6. The genetic variation of the population in our simulation _____(decreased / increased)_____.
Explain why this happened. __________________________________________________
_______________________________________________________________________
Continue on back.
Name _________________ # ____
Mrs. Geithner-Marron Bio 200
Natural Selection: For the Birds
Period _______
Date ________
7. If only one species is considered to be the “fittest”, why are there still so many variations
among species? (Ex. Why do some birds have very long pointy beaks, while other birds have
short, flat beaks?) ________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
8. An environmental change causes nectar (sugar-water) to be the only available food source.
a. What would happen to the “beak” phenotype that originally was the best adapted (see
question 2)? Defend your answer. __________________________________________
___________________________________________________________________
___________________________________________________________________
b. With the new food source (nectar/liquid sugar), which “beak” phenotype would NOW be
best “adapted” (to feed on nectar)? Why? ___________________________________
___________________________________________________________________
___________________________________________________________________
9. How might natural selection result in extinction? __________________________________
_______________________________________________________________________
_______________________________________________________________________
10. How did this simulation help to improve your understanding of natural selection and evolution?
Explain your answer. _______________________________________________________
_______________________________________________________________________
_______________________________________________________________________