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Evolution through natural selection: A simple simulation
What your lab notebook should contain:
1. Name of Lab, your name and your partner’s name
2. Objective
3. Collected data
4. Evaluation questions
5. Conclusion
Objectives: This is an observational lab, wherein you will do simulations that help to understand the
Basic principles of evolution through natural selection.
When you finish this lab, you should:
1. Understand how prey phenotype, predation and the environment interact to determine prey
fitness (natural selection)
2. Understand how differences among prey in fitness produces, across generations,
differences in mean phenotype (evolution)
I. Background:
By the mid1800s, the term "evolution" was already in use to describe observed changes in
heritable phenotype across generations, but natural historians of the time disagreed about the cause
(forces) of these changes. Darwin and Wallace's great breakthrough was to recognize that evolution
could be explained by individual differences in reproductive success (number of offspring). Darwin's
term for this was "natural selection," parallel to the already accepted term of "artificial selection"
used to describe breeding programs for domesticated plants and animals.
For populations to evolve, they must possess two attributes:
a. there must be variation in phenotype among individuals
b. the variation among individuals is heritable (due to genetic differences - variation)
If there is no variation in a particular characteristic, such as number of legs, then no matter how
favorable it might be to have six or eight legs, that trait cannot evolve. Similarly, a change in a trait
can only evolve if the variation is genetically determined. Tattoos are not genetically determined and
so the frequency of tattooing cannot change through biological evolution. Note that any observed
phenotype can be tested for evolutionary change; quantitative (number of legs) and qualitative (color)
traits can both evolve. If there is no correlation of phenotype to number of offspring, any
evolutionary changes will be random. We call this genetic drift.
By adding a third criterion to our list, evolution becomes non-random:
c. individuals with a particular phenotype leave more offspring
We are now proposing that selection favors some phenotypes over others. In natural selection, the
environment presents challenges that some individuals overcome more easily than others as a result
of their traits. Individuals with particular phenotypes may leave more offspring than others for a
variety of reasons: they are more efficient at gathering resources and growing, they survive longer,
they have more opportunities to mate, or they have healthier offspring. This is differential fitness,
meaning that some individuals produce more offspring than others. Over successive generations, the
phenotypes of individuals with higher fitness will become more common in the population.
Differential fitness, favoring one phenotype over another, will produce a change in the average
phenotype of the population; this means evolution has occurred. Importantly, note that selection
occurs among individuals in one generation, while evolution occurs in a population across
generations.
Darwin sorted selective forces into two categories. Natural selection is imposed by the environment
on the individual. Sexual selection is imposed strictly by the behaviors and conditions surrounding
mating. In this lab, we are going to focus on natural selection as the mechanism for evolutionary
change in a population of beans of three colors.
Bean Population Part 1
You will simulate natural selection in a bean population and test the following hypothesis.
Hypothesis: Organisms (beans) that blend into their environment will possess greater fitness than
organisms that are more visible.
Procedure Part 1:
1) Choose one student to be record keeper.
2) Count out 20 of each color of bean and mix them together into a container.
3) The record keeper distributes the beans on the cloth while everyone else looks away.
4) Each "predator" has 30 seconds to capture beans with a set of tweezers and transfer them
to a container.
5) At the end of 30 seconds, all predation must stop. Beans in process of being captured
"escape".
6) Count up the total number of captured beans in each color, and subtract from the original
20. The remainders are the ones that survived, and they are allowed to produce 2
offspring each. Record your totals in Table 1.
7) Add the surviving beans along with their offspring to the cloth and repeat the procedure
for two more generations.
8) After each generation, perform the same calculations and record your totals in Table 2
and 3.
Sample calculation:
For generation 0: 20 white beans
Number captured by predators: 12 white beans
Number of survivors: 20-12 = 8 white beans
Number of offspring: 8 survivors x 2 offspring each = 16.
For generation 1, add 24 white beans: 16 white beans (offspring) + 8 white beans (surviving).
Predictions: (RECORD your answers on a separate page.)
Considering your selective environment, what differences in fitness do you expect between
individual beans of different colors?
Data Tables
Table 1
Background:
Generation 0
Captured 1
Surviving 1
Offspring 1
Generation 1= Surviving +
Offspring
Color 1
20
Color 2
20
Color 3
20
Color 4
20
Captured 2
Surviving 2
Offspring 2
Generation 2= Surviving +
Offspring
Captured 3
Surviving 3
Offspring 3
Generation 3= Surviving +
Offspring
Table 2
Background:
Generation 0
Captured 1
Surviving 1
Offspring 1
Generation 1= Surviving +
Offspring
Captured 2
Surviving 2
Offspring 2
Generation 2= Surviving +
Offspring
Captured 3
Surviving 3
Offspring 3
Generation 3= Surviving +
Offspring
Table 3
Background:
Generation 0
Captured 1
Surviving 1
Offspring 1
Generation 1= Surviving +
Offspring
Captured 2
Surviving 2
Offspring 2
Generation 2= Surviving +
Offspring
Captured 3
Surviving 3
Offspring 3
Color 1
20
Color 2
20
Color 3
20
Color 4
20
Color 1
20
Color 2
20
Color 3
20
Color 4
20
Generation 3= Surviving +
Offspring
Evaluation:
What did you observe for the bean population as a whole? For each type of colored bean?
Do your results support the hypothesis or not? Explain what has happened in your own words.
Compare your results to one other group with the same environment. Did you see the same pattern of
evolutionary change? Why or why not?
Make a list of ALL factors you can think of that could influence the evolution of the bean population.
Conclusion:
Write a conclusion for the lab activity; be sure to include the following:
 Describe the lab
 Explain why the lab was performed
 Describe the procedure
 Analyze your results (Did the support your hypothesis?)
 Any questions that were answered/any questions that you might have now that you
done the experiment
Remember the conclusion should be in complete sentences and should not have any bullet points or
lists.