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Evolution by Natural Selection “Bean” Lab
Background:
Natural selection was a theory proposed by Charles Darwin that can explain how species may change
over time. Natural selection can also help scientists to explain the fossil record of ancient life forms and
the similarities that we see among diverse organisms. Species evolve over time. There are four things
that drive or allow evolution by natural selection to occur:
1.
2.
3.
4.
Organisms tend to reproduce/increase in population
There are naturally variations among organisms
There is a limited supply of resources available in the organisms’ environment
The offspring that are better able to survive (more “fit”) leave offspring of their own with
similar inherited traits
The driving force of number four (above) is the primary emphasis of this activity
Survival of the Fittest:
Why do some organisms survive while others die?
The successful survival and reproduction of an organism depends on several environmental factors.
These factors may include (1) predator-prey relationships, (2) resource shortages, (3) change of habitat.
In any generation, only a small percentage of organisms survive. Survival depends on the DNA (genes)
of the organism and the inherited traits that will, given circumstances such as limited resources, give a
greater chance (probability) of survival and reproduction.
Purpose:
In this activity, you will experience one mechanism for evolution through a simulation that models the
principles of natural selection and helps answer the question: How might biological change (evolution)
have occurred and been reinforced over time?
Pre-lab:
Complete the pre-lab questions on the next page and get approval from Mr. Tran prior to grabbing any
materials or beginning any simulations!
Materials:
1 plastic bag labeled “beginning population”
3 plastic bags (1 each of black, red, and white beans)
2 forceps
Timer
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Pre-lab Questions:
1) Who first proposed the theory of evolution by natural selection?
2) What evidence from long ago can explain why very different looking organisms may actually share a
common ancestor?
3) What four things drive evolution by natural selection?
1.
2.
3.
4.
4) What are three examples of factors that may affect the successful survival and reproduction of an
organism?
1.
2.
3.
5) What does survival under the above conditions ultimately depend on?
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Procedure:
1) Write a hypothesis
We know that organisms are tightly tied to their environments. Based on the background color of
your habitat, what color bean do you predict will be the predominant variation after four
generations? Use an “if… then…” statement (ex. If the number of red beans is greater than the
number of white or black beans by the end of round 4, then the red variation of bean is the best
variation for the pink background environment)
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2)
Simulate!
 Each pair of forceps represents a predator
 Each generation will be simulated by 30 seconds of predation
 After each round, each surviving bean will have 3 offspring of the same variation added to
the habitat to simulate reproduction
Procedure:
1. In your group, pick a “game warden” and two members to be the predators.
2. The game warden will pick up one bag containing the prey (bean types) to use in this experiment. Also
pick up 2 forceps for the predators to use.
3. Pick 10 beans from each bag and add them to the plastic bag labeled, “Beginning Population”. Each
type represents a different species. Record the total number of prey in your data table.
4. The game warden will tell the predators to turn away from the habitat. The game warden will then
spread the prey in the “Beginning Population” across the habitat. He/she then tells the predators to turn
around and gather prey, ONE AT A TIME, using a forceps. The predators must stop when the game
warden says, “STOP” after 30 seconds.
5. After the hunting is stopped, students should determine how many prey are left in the habitat. Count
the number of each type of prey that the predators have captured. Subtract the number of captured
prey from the starting number; this is the number left in the habitat. The game warden is responsible for
recording these data in the data table 1.
6. To simulate reproduction among the prey, add 3 beans for each remaining bean of every type. These
beans, obtained from the bags containing extra beans, represent offspring. (surviving number X 3 =
offspring to be added to the environment)
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7. Repeat the predation using the second generation of beans (Start # for Gen. 2 = survivors from 1st
generation plus new offspring). Again, record the number of remaining (surviving) prey for the second
generation.
8. Repeat the simulation of reproduction among the surviving prey as before until you have a beginning
number of prey to start round 4. Instead of having the predators hunt again, you may simply calculate
the number of individuals that would be in the fourth generation’s start population.
9. Share your data on the board, so that the class can get your data. Copy this data in the second lab
table.
10. Re-sort the types of beans into the appropriate bags.
3) Collect Data
Group Data for ____________________________________ colored environment
Species
Start for
round 1
Black
10
Red
10
White
10
Surviving
at end of
round 1
Start for
round 2
Surviving
at end of
round 2
Start for
round 3
Surviving
at end of
round 3
Start for
round 4
Start for
round 2
Surviving
at end of
round 2
Start for
round 3
Surviving
at end of
round 3
Start for
round 4
Class data for all environments
Species
Start for
round 1
Surviving
at end of
round 1
Black
Red
White
To calculate number to start each round:
# surviving at end of round x 3 new offspring = # of that variation to start next round
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4) Analyze the Data
Create two graphs in Microsoft excel:
a) Bar graph of the number of prey surviving at the beginning of each generation for your group’s
habitat
b) Bar graph of the average number of each type of prey surviving after each round for the entire
class’s data set
All graphs must be properly labeled including: title, x axis (horizontal) title, y axis (vertical) title,
legend/key. See class page for help!
5)
Write a conclusion
Your conclusion must answer the following questions:
-Was your hypothesis correct for your group’s given environment? Why or why not?
-Which types of prey survived better than others in the second and third generation populations?
Why might these prey have been more successful/fit?
-What effect did capturing a particular type of prey have on the numbers of that type in following
generations?
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6) Draw your group’s evolved species
Based on your group’s data, imagine which of the three variations of beans your species would
evolve into after 10,000 generations of offspring. Then draw this version of the bean in color below.
Species Name:
Habitat Color:
Adaptations:
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