Name: ________________________________________________________________________Date: _________________________ Block: ________
Evolution by Natural Selection
Class Activity and Individual Summative Assessment
Adapted from Jennifer Doherty and Dr. Ingrid Waldron, Department of Biology, University of Pennsylvania
Pre-lab activities
Living things that are well adapted to their environment survive and reproduce. Those that are not well
adapted don’t survive and reproduce. An adaptation is any characteristic that increases fitness. Fitness is the
ability to survive and reproduce.
Examine the image below. Describe what is happening in figures 1-3. Is the population of mice different in
figure 3 than in figure 1? Explain why.
What characteristic of the mice is an adaptation that increased their fitness?
The table below gives descriptions of four female mice that live in a beach area which is mostly tan sand with
scattered plants. According to the definition given for fitness, which mouse would biologists consider the
fittest? Explain why this mouse would be the fittest.
Color of fur
Black
Tan
Cream
8 months
11
Tan and
Black
4 months
3
Age at death
# pups produced by each
female
Running speed
2 months
0
8 cm/sec.
6 cm/sec.
7 cm/sec.
5 cm/sec.
2 months
0
If a mouse's fur color is generally similar to its mother’s color, what color fur would be most common among
the pups?
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A more complete definition of fitness is the ability to survive and produce offspring who can also survive
and reproduce. Below are descriptions of four male lions. According to this definition of fitness, which lion
from the table below would biologists consider the “fittest”? Explain why.
Name
Age at death
# cubs fathered
# cubs surviving to adulthood
Size
George
13 years
19
15
10 feet
Dwayne
16 years
25
14
8.5 feet
Spot
12 years
20
14
9 feet
Tyrone
10 years
20
19
9 feet
Suppose that Tyrone had genes that he passed on to his cubs that helped his cubs to resist infections, so they
were more likely to survive to adulthood. These genes would be more common in the next generation, since
more of the cubs with these genes would survive to reproduce.
A characteristic which is influenced by genes and passed from parents to offspring is called heritable. Over
many generations heritable adaptive characteristics become more common in a population. This process is
called evolution by natural selection. Evolution by natural selection takes place over many, many
generations.
Evolution by natural selection leads to adaptation within a population. The term evolution by natural selection
does not refer to individuals changing during their lifetime, only to changes in the frequency of adaptive
characteristics in the population as a whole. For example, for the mice that lived in the beach area with tan
sand, none of the mice had a change in the color of their fur; however, due to natural selection, tan fur was more
common for the pups than for the mother mice.
The following table shows a population of mice over three generations:
Mouse color
# of individuals in generation 1
# of individuals in generation 2
# of individuals in generation 3
Black
5
8
12
Tan
5
3
1
Cream
5
1
0
How many mice total are there in generation 2?
How many mice are black in generation 2?
What is the frequency of black mice in generation 2? (To do this, calculate the percentage that are black in
generation 2 out of the total number of mice in generation 2).
Complete the following table with the frequencies (percentages) of each mouse color in each generation:
Mouse color
Frequency of color in generation 1
Frequency of color in generation 2
Frequency of color in generation 3
Black
Tan
Cream
In summary, a heritable characteristic that helps an animal or plant to have more offspring which survive to
reproduce will tend to become more common in a population as a result of evolution by natural selection.
From the frequency data table above, what can you conclude about the effect of mouse color on natural
selection in the mouse population?
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Simulation of Natural Selection
We will now play a simulation game to demonstrate how natural selection works.
A simulation is a good way to simplify the problem in such a way that we can observe how evolution by natural
selection may work in a real population. This simulation involves beans that can reproduce. These beans live
out their lives in a Brown Forest or Red Grassland habitat in the middle of the classroom. The only concern our
beans creatures have is the presence of ravenous hunters (that’s you!). All we need is a system that has three
necessary conditions for evolution by natural selection.
A. Variation in characteristics: For natural selection to occur, different individuals in a population must
have different characteristics. In our simulation, beans vary in color; they are brown, red, and white.
The hunters vary as well; hunters have three distinct types of feeding structures: forks, knives, and
spoons.
B. Differences in fitness: For natural selection to occur, the different characteristics of different
individuals must contribute to differences in fitness (i.e. differences in ability to survive and reproduce).
It seems possible that variation in bean color will influence the probability that a bean is snatched up by
a hungry hunter. It also seems possible that different feeding types may vary in their success in
capturing beans. These differences contribute to survival and therefore success in reproducing.
C. Heritability of characteristics: For natural selection to occur, the characteristics that affect fitness
must be heritable (i.e. passed by genes from one generation to the next). In our simulation, a bean that
is born into the bean population is the same color as its parent and a hunter that is born into the hunter
population has the same feeding structure as its parent.
Before the simulation, make two hypotheses, one about bean survival and one about hunter survival.
Remember that a hypothesis should be written in the “if…, then…” format. Your hypotheses should be specific
and answer the following questions:
1. Which color bean do you think will be more likely to survive in each habitat? Why?
2. Which feeding structure do you think will do better in each habitat? Why?
Here is exactly what we will do:
1. Your class will be split into two groups which will carry out the simulation using two different habitats:
Brown Forest and Red Grassland.
2. Beans come in three colors: brown, red, and white. Your teacher will “plant” an equal number of each color
on the Brown Forest and on the Red Grassland at the beginning of the simulation.
3. Now it is time to arm the hunters. There are three different feeding types: forks, knives, and spoons. Your
teacher will distribute the feeding structures so that there are equal numbers of each. You will also be
given a cup. This cup will serve as your “stomach”. To capture a bean, you must use only your fork, knife or
spoon to lift the bean from the habitat and put it into your cup. You may only capture and eat 1 bean at a
time.
4. Your teacher will record the initial numbers of each type of bean and each type of hunter in each habitat.
5. At your teacher’s signal, start feeding according to the following rules.
a. You may not yell, scream, hit, throw, push or behave in any way that inappropriate for the classroom.
b. You may not tilt your cup in any way.
c. You may eat only one bean at a time.
d. Once a bean is on someone’s feeding structure it is off limits (no knocking beans off feeding structures).
Failure to follow any of the rules will result in your immediate death in the simulation and you will
not be allowed to continue hunting.
When your teacher calls time, STOP feeding.
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6. Now count how many beans you have eaten and line up with your classmates who were feeding on the
same habitat, from fewest beans eaten to most beans eaten. Only the top half of the hunters will survive
and reproduce. Your teacher will tell you who lives and who dies. Those who die will be reborn as the
children of the survivors and will now have the same type of feeding structure as their parents had.
7. Your teacher will count how many beans of each color were eaten, calculate how many beans survived, and
help the surviving beans reproduce. Only the beans that were not eaten will reproduce.
8. You will run through the simulation one more time. Your teacher will post on the board the numbers of
beans of each color and hunters of each type at the beginning of the simulation (generation 1) and at the
end of each cycle (generations 2 and 3). Copy down the numbers in your table you are making.
Your 2 bean tables will look something like this:
BROWN habitat
Bean color
# of individuals in generation 1
# eaten
# remaining (survive to
reproduce)
# new (offspring)
# of individuals in generation 2
# eaten
# remaining (survive to
reproduce)
# new (offspring)
# of individuals in generation 3
Red
Brown
White
And your 2 hunter tables will look something like this:
Hunter type
# in generation 1
# in generation 2
# in generation 3
Knife
Fork
Spoon
Prepare your data tables in your notebook now. Remember, you will need four tables: bean populations in both
the brown and the red habitat, and hunter populations in both habitats.
Analyzing your data
After the simulation is finished, you will need to analyze your data in Excel. Remember:
The term evolution by natural selection does not refer to individuals changing,
only to changes in the frequency of adaptive characteristics in the population as a whole.
To calculate the frequency, you will need to calculate the percentage of each color in each habitat in each
generation. Make four new tables in your notebook. Each table will have 9 numbers (for the three variations
and the three generations). Each number will be a percent.
To visually represent this data, you will use these numbers to make four charts (beans and hunters in both
brown and red habitats). Decide which type of chart will best represent your data. Remember that your chart
should accurately reflect your data and should include:
1. A detailed and descriptive chart title
2. Descriptive Axis Labels
3. If necessary, a key identifying your data series
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Post-lab report (individual summative assessment)
After we have finished the simulation in class, you will need to take your information home and individually
complete the summative assessment. This assessment will be in the style of the formal lab report like we did
last semester. Please refer to the formal lab report format and rubric for information on how to write your
report. However, you will not need to include all of the sections in your formal lab report. You only need to
include the following sections:
1. Hypothesis
Two hypotheses, one for beans and one for hunters, in the “if…, then…” format.
2. Data
Minimum four data tables showing the frequency (percents) of each allele in the population for each
generation.
3. Graphs
Four graphs displaying the change in allele frequencies over four generations in the different populations in
each habitat.
4. Analyses
Within your analysis you must include the answers to the following questions:
 Did evolution by natural selection occur in each bean population? In other words, did one bean
color become more common over time while the other colors became less common? What traits
contributed to the survival of beans that survived to reproduce?
 For each population of hunters, did one feeding type become more common while other feeding
types became less common? What traits contributed to the survival of hunters that survived to
reproduce?
 If we ran the simulation for 50 more generations, what would you predict about the colors of the
beans and the hunter types in each habitat?
However, because this is a lab report do NOT re-type the questions into your report. Do not only answer
the questions, but include all the information that is normally required in an analysis section. The
questions are here to guide you towards including all the required ideas.
5. Conclusion
Within your conclusion you must include the answers to the following questions:
 Explain why evolution by natural selection cannot occur if the variation in a characteristic does not
contribute to differences in fitness. Suppose, for example, that all the hunters in the simulation
were blind-folded and could only find beans by touch. Would you expect evolution by natural
selection in the color of the beans?
 Explain why evolution by natural selection can not occur if the variation in a characteristic is not
heritable. Suppose, for example, a tree limb fell on a young lion and broke his leg, and the leg never
healed normally. Obviously, this would affect the lion's ability to survive and reproduce. However,
if this lion did manage to have cubs, the offspring would each have four normal legs. Explain why
natural selection does not operate on characteristics like this which affect fitness but are not
heritable.
 "Survival of the fittest" is a common expression. What do you think most people mean by this
expression? How would you explain this expression to help someone understand how natural
selection actually functions?
However, because this is a lab report do NOT re-type the question into your report. Do not only answer the
questions, but include all the information that is normally required in a conclusion section. The questions
are here to guide you towards including all the required ideas.
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Your report will be graded according to selected sections from the formal lab report rubric. They are:
CATEGORY
Hypothesis
x2
4
Hypothesized relationship
between the variables and
the predicted results is
clear and reasonable based
on what has been studied.
Data/
Observations/
Results
x2
The results are properly
graphed or grouped. There
is a comparison and
analysis among the results.
All data have units.
The graph correctly and
clearly displays the results
with units. If applicable
there is a trend line.
The analysis summarizes
the data trends on the
results/graph.
Conclusion is clearly
written and insightful, and
goes beyond the required
information to provide
interesting details about
the experiment and future
experiments.
Graph
x2
Written Analysis
x4
Conclusion
x5
3
Hypothesized
relationship between the
variables and the
predicted results is
reasonable based on
general knowledge and
observations.
Results are presented
clearly and accurately
described. All data have
units.
The graph correctly
shows the results with
units but not in a clear
way.
The analysis partially
summarizes the trends
obtained in the results.
Conclusion is clearly
written and includes
whether the findings
supported the hypothesis,
possible sources of error,
and what was learned.
2
Hypothesized relationship
between the variables and
the predicted results has
been stated, but appears to
be based on flawed logic.
1
The hypothesis that has
been stated in the lab is
erroneous or irrelevant.
0
No hypothesis
is stated.
The results of the lab are
partially identified, and are
stated in a somewhat
unclear manner. There are
no units.
The graph does not
correctly show the results
or there are no units.
The results of the lab are
erroneous or irrelevant or
were not done on the
computer.
No results
presented
The graph does not show
the results or was not
done on the computer.
No graph
presented.
The analysis is unclear and
erroneous.
The analysis is irrelevant.
No analysis
presented.
Conclusion is somewhat
unclearly written, but
includes whether the
findings supported the
hypothesis what was
learned from the
experiment.
Conclusions show little
effort and reflection
and/or is not written in a
clear manner.
No
conclusions.
This individual summative assessment is due: _______________________________________________.
You may choose to turn in your report on paper or by email. In both cases it is due when the bell rings for the
start of class on the due date. Any assignments turned in after this date will be deducted 20% each day.
Remember that this is an individual assessment. Any suspected incidences of plagiarism will be referred to the
Dean.
This document, the formal lab report format and rubric can all be found on the class website.
Good luck and have fun!
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