Name ____________________________________ #______
Date ___________________
Ms. Geithner-Marron Bio 300
Period _________________
“Natural Selection: For the Birds” lab
Problem: How can variation in a population lead to natural selection (of certain phenotypes) and evolution within a
population?
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
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 not. This change in populations (and species), over time, is
evolution; natural selection is the mechanism (or driving force) behind evolution.
Materials:
 copies of concept map, lab, and exit ticket (1 per student—concept map & exit ticket can be projected or copied)
 wipe boards
 dry erase markers
 dry erase board erasers (or tissues/paper towels)
 computer (optional)
 graph paper (or graphing software)
 tray (1 per group) (or just mark off an area on the table using tape)
 timers (1 per group)
 “food” (kidney beans or similar—approximately ½ -1 bag per group)
 “stomach” (small bathroom cups or similar—1 per student)
 “beaks” (several different types of tools—Have at least as many of each type as there are students in the class.)
o Examples: pipette/dropper, straw, dissecting needle/nail/toothpick, drink stirrer, spoon, popsicle stick,
tweezers/forceps, tongs, clothes pins, test tube clamp, (safety) scissors
 containers to hold “beaks” (optional)
Procedure
1. Obtain “beaks” from containers in materials area (or these may already be left for students at the lab tables… If there are
7 students in each group, there should be seven of each type of “beak” at the table.)
a. Initially, there should be an equal number of each “beak” phenotype represented in the “parent” group (if
possible). (If there are more beak types than students, ask the teacher which should not be used.)
b. Create a data table similar to the examples below and 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 generation on table 1.
2. Spread “food” over the feeding area. (Tray on table or marked off area.)
Name ____________________________________ #______
Date ___________________
Ms. Geithner-Marron Bio 300
Period _________________
“Natural Selection: For the Birds” lab
3. Hypothesize: Which “beak” phenotype do you think will be “naturally selected” for in this simulation. Explain your
reasoning… ______________________________________________________________________________________
_________________________________________________________________________________________________
4. Placing one hand behind their backs and keeping both feet on the ground (without pushing, hitting, etc.), everyone will
have 30-60 seconds (as directed) to obtain “food” from the feeding area using only their “beaks” (in the way that was
demonstrated) and place the seeds into their “stomach”. (One person should be responsible for timing each round.)
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”. If the “food” falls in the feeding area, it can still be “eaten” if it is caught again.
b. Any “food” that is not in the “stomach” when time is called does not count.
c. Food can be “stolen” from another “bird” only within the feeding area.
5. The pieces of food “eaten” by each individual will be counted, recorded in table 2 (under the corresponding generation),
and then returned to the common area.
6. To determine which “beak” phenotypes will be represented in the next generation:
a. The individual that “ate the least” will not survive.
i. The individual that did not survive will become the “offspring” of the individual that “ate the most” and
was able to successfully reproduce. (The individual that did not survive will return their unsuccessful
“beak” to the materials area and take the tool representing the new “beak” phenotype they will have in
the next generation.)
b. The organisms with the other “beak” types will reproduce “offspring” with the same “beak” phenotype. (For the
next round, they will have the same “beak” and will not change which tool they are using.)
c. Fill in the number of individuals with each “beak” phenotype for the upcoming “offspring” generation (F1, F2,
etc.) on table
7. Repeat steps 2-5 until time is called, you should, however, have at least five generations of data (parent and F1-F4
offspring).
a. If you get to a point, where there is only one “beak” phenotype. Make a new set of data tables and label them
“Trial 2”, then run the simulation again from the beginning.
Sample Data Tables
Table 1: # of Individuals with Each “Beak” Phenotype in Population
Table 2: # of Seeds Eaten by Each “Beak” Phenotype per Generation
Name ____________________________________ #______
Date ___________________
Ms. Geithner-Marron Bio 300
Period _________________
“Natural Selection: For the Birds” lab
Data Analysis:
1. Graph the number of individuals with each “beak” phenotype over time (generations) using a different line for each “beak”
phenotype. If you have more than one trial, use the trial that had the most generations.
a. What is the independent variable? On which axis should this variable be plotted?
b. What is the dependent variable? On which axis should this variable be plotted?
c. What variables are controlled (kept constant)?
2. On a separate set of axes, graph the number of seeds over time (generations) using a different line for each “beak” phenotype.
If you have more than one trial, use the trial that had the most generations.
a. What is the independent variable? On which axis should this variable be plotted?
b. What is the dependent variable? On which axis should this variable be plotted?
c. What variables are controlled (kept constant)?
3. Which “beak” phenotype was best adapted for the type of “food” that was available (in our simulation)? Explain your
reasoning.
4. Which “beak” phenotype was least adapted for the type of “food” that was available (in our simulation)? Explain your
reasoning.
Discussion Questions (Answer on a separate sheet of paper. Incorporate the question wording into your answer.):
1. How does genetic variation allow a population to survive during environmental changes (such as a change in the type of food
available)?
a. An environmental change causes nectar to be the only available food source.
i. What would happen to the “beak” phenotype (from our simulation) that originally was the best adapted?
Defend your answer.
ii. In the new conditions, which “beak” phenotype would NOW be best “adapted” (to feed on nectar)?
Why?
2. What causes genetic variation in a population? Name at least 2 different sources of variation and explain how they contribute
to genetic variation.
3. What happened to the genetic variation of the population in our simulation? Describe why this happened.
4. 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?)
5. How might natural selection result in extinction?
6. What are some of the benefits of this simulation? What are some of the drawbacks of this simulation?
7. What are some errors that might have affected the outcome of this simulation? What could be done to minimize them?
8. Did the simulation help you understand natural selection and evolution better? Explain your answer.
Conclusions:
1. Write at least one paragraph explaining how this simulation and its results demonstrate the process of natural selection and
support the theory of evolution.
Name ____________________________________ #______
Date ___________________
Ms. Geithner-Marron Bio 300
Period _________________
“Natural Selection: For the Birds” lab
Natural Selection Concept Map
Theory of
Natural Selection
Exit Ticket
The diagram to the right shows four species of birds that evolved from an ancestral species that had a
small, pointed beak. Today, all four species inhabit the same island.
1.
Which statement best explains the variation in the beaks of these four species?
(A) Over time, an abundance of seeds for food led to increased similarities between the species.
(B) Over time, an abundance of seeds for food led to increased differences between the species.
(C) Competition for limited food resources led to selection for similar traits.
(D) Competition for limited food resources led to selection for different traits.
Base your answers to questions 2 and 3 on the diagram below that shows variations in the
beaks of finches in the Galapagos Islands and on your knowledge of biology.
2.
The diversity of species seen on the Galapagos Islands is mostly due to
(A) gene manipulation by scientists
(B) gene changes resulting from mitotic cell division
(C) natural selection
(D) selective breeding
3.
State one reason why large ground finches and large tree finches can coexist on
the same island.