Activity Template
Subject Area(s)
Life Science
Associated Unit
None
Associated Lesson
Activity Title
None
Natural Selection In Action: Tadpoles vs. Crayfish
Header
Image 1
ADA Description: ___?
Caption: ___?
Image file name: ___?
Source/Rights: Copyright © ___?
Grade Level _7 (6_-_8)
Activity Dependency
Time Required
None
3 class periods of 52 minutes
Group Size 28
Expendable Cost per Group US$20
This does not include the costs of laminating the cards since most schools have
laminators available.
Summary
The purpose of this activity is to simulate evolution by natural selection. Students will
participate in a game in which predators (crayfish) and prey (tadpoles) face off; tadpole
tail size is the trait under selection in this simulation. Students will make predictions
about what will happen after several rounds of predation and reproduction, play the
game, reassess their predictions, and graph the distribution of tadpole tail sizes after
predation.
Engineering Connection
Engineers use models to simulate natural phenomenon, as students will do in this
exercise. Further, students practice graphing and interpreting data, crucial skills in
engineering and science.
Engineering Category
Choose the category that best describes this activity’s amount/depth of engineering
content: (1) relates science concept to engineering, (2) relates math concept to
engineering, (3) provides engineering analysis or partial design, or (4) provides
complete engineering design process. Or (5) does not include any engineering content.
1 or 5
Level of Inquiry
Level 2: Structured Inquiry: students investigate a teacher-presented question through a
prescribed procedure.
Keywords
adaptation, evolution, game, graph, natural selection
Educational Standards
1) CA State Standards addressed:
7th Grade Science
Genetics
7.2b. Students know sexual reproduction produces offspring that inherit half of their
genes from each parent.
7.2c. Students know an inherited trait can be determined by one or more genes.
Evolution
7.3a. Students know both genetic variation and environmental factors are causes of
evolution and diversity of organisms.
7.3b. Students know the reasoning used by Charles Darwin in reaching his conclusion
that natural selection is the mechanism of evolution.
7.3e. Students know that extinction of a species occurs when the environment changes
and the adaptive characteristics of a species are insufficient for its survival.
Investigation and Experimentation
7a. Select and use appropriate tools and technology (including calculators, computers,
balance, spring scales, microscopes, and binoculars) to perform tests, collect data, and
display data.
7c. Communicate the logical connection among hypotheses, science concepts, tests
conducted, data collected, and conclusions drawn from the scientific evidence.
7d. Construct scale models, maps, and appropriately labeled diagrams to communicate
scientific knowledge.
7e. Communicate the steps and results from an investigation in written reports and oral
presentations.
Math
Statistics, Data Analysis, and Probability 1.0
Students collect, organize, and represent data sets that have one or more variables and
identify relationships among variables within a data set by hand and through the use of
an electronic spreadsheet software program:
1.1 Know various forms of display for data sets, including a stem-and-leaf plot or boxand-whisker plot; use the forms to display a single set of data or to compare two sets of
data.
2) National Standards addressed:
Science as Inquiry Standards Levels 5-8
Abilities necessary to do scientific inquiry
Understanding about scientific inquiry
Life Science Standards Levels 5-8
Populations and ecosystems
Diversity and adaptations of organisms
Science in Personal and Social Perspectives Levels 5-8
Populations, resources, and environments
Pre-Requisite Knowledge
Students should have learned about the concepts of evolution and natural selection
already. They should also be familiar with how to calculate an average.
Learning Objectives
After this activity, students should be able to:
 Describe how natural selection works
 Relate the environmental conditions to whether or not a trait is adaptive
Materials List
To share with the entire class:
 Color print outs of tadpole cards, crayfish signs, and other signs indicating stations
 Laminating machine to laminate cards and signs
 2 quarters
 Calculators for 2nd and 3rd days (or have students bring their own or borrow from
math teacher)
 Clipboard for data recorder
 Paper for handouts (see attachments)
Introduction / Motivation
I had previously described my research to the students. In the Santa Monica Mountains,
there are non-native crayfish in the streams that are eating the native tadpoles. I am
researching whether the tadpoles are adapting to the crayfish and whether they are
evolving any anti-predator traits to help them avoid being preyed upon by crayfish.
Before beginning the game, I reminded the students about the tadpoles and crayfish in
the Santa Monica Mountains and told them about how the introduced crayfish are eating
the tadpoles. I started by asking the students about what traits they thought might be
important for tadpoles to have to avoid being eaten by crayfish. I also asked students to
define natural selection and we discussed that concept.
Vocabulary / Definitions
Word
Definition
Natural
The process by which individuals that are better adapted
selection
to their environment survive and reproduce more successfully than less
well adapted individuals; theory to explain the mechanism of evolution
Adaptation A characteristic that improves an individual’s ability to survive and
reproduce in a particular environment
Evolution
The process in which inherited characteristics within a population change
over generations such that new species sometimes arise
Trait
Native
species
A genetically determined characteristic
A species that is found in a particular region as the result of only natural
forces, without human intervention
Non-native
invasive
species
Crayfish
A species that is found in an area outside of its natural range due to
human activity – frequently that species has negative impacts
Crustacean that lives in fresh water – looks like a small lobster
Procedure
DAY 1
Tell the students that you went to a stream in the Santa Monica Mountains and
collected tadpoles and you found that they had very different sizes of tails. You also
noticed that there were crayfish in the streams (not native) that were eating the
tadpoles. You then wondered if tail size might be important for determining whether a
tadpole could escape predation by a crayfish.
Ask the students how tail size might help or hurt a tadpole in escaping predation.
Have them write down their hypothesis on “Hypothesis Handout” (Question1).
Go over how the game will be played generally with an overhead schematic image –
attached file “Game Schematic”
Start by splitting up the class:
1 student will be the game leader
1 student will be the data recorder (will get a data sheet)
16 students to the tadpole group
2 students will be crayfish
remaining students will be next generation of tadpoles
Round 1:
Give instructions to the game leader, have them follow instructions and tell other
students what to do (help them as needed)
16 students that are tadpoles will select a card from the tadpole pile of cards – each
student will be a tadpole with a specific sized tail that will be represented by an
image and by a “tail score”
Tail scores and the distribution of tail sizes are indicated in the tables below:
Tail
Score
2 (worst)
3
4
5
6
7
8 (best)
Number
1
2
3
4
3
2
1
After tadpoles have received their tail sizes have them sit down and have the data
recorder call out the tail scores and record the number of students with that tail score
(can indicate by raising hands)
Students that are crayfish will stand by the crayfish stations (denoted by a crayfish sign)
Simulate Predation:
Tadpoles will split up into approximately equal groups at each crayfish station
When it is their turn, the crayfish student flips a quarter
If the quarter shows heads: the tadpole does not encounter a crayfish and
survives
If the quarter shows tails: the tadpole encounters a crayfish
The tadpole escapes predation and survives if their tail score is 6 or
greater
The tadpole is eaten is if their tail score is 5 or less
Dead tadpoles go to “Dead Tadpoles” area and return their card to the ordered piles
Surviving tadpoles go to “Survivor Tadpoles” area and get ready for reproduction
Reproduction:
After all tadpoles have gone through the predation cycle, the surviving tadpoles
reproduce
If you are a surviving tadpole: you reproduce and create 2 new tadpoles
Since tail size is a heritable trait, offspring are similar but not identical to their
parent (ask the students what is one simplification here? Answer: We are
using only one parent in reproduction)
One surviving tadpole produces two offspring, one with a tail size one
level smaller than the parent, and one with a tail size one level higher than
the parent (for instance, if the parent tail score is 6, they will produce 2
offspring, 1 with tail score 5, and one with tail score 7)
You can get tail scores greater than 8 and less than 2, but not less than
zero
Have each surviving tadpole go through reproduction; the game leader should take the
original card and hand out the new cards; the parent tadpole dies
Two new students become offspring, if not enough students have dead tadpole
or parent come back to life as an offspring or have students hold 2 cards
This is the end of Round 1
Before beginning Round 2, the data need to be recorded
Have all students sit down for the data to be recorded
Have the data recorder write down the numbers of tadpoles with different tail scores as
was done before
Round 2:
All tadpoles go through predation process again with the same rules as before
All surviving tadpoles go through reproduction process as before
Tally number at end of Round – record on data sheet by data recorder
Repeat Rounds 3 times total
At end, have students answer Question 2 from the “Hypothesis Handout”
DAY 2
Pass out Data Analysis Handout
Have students work in pairs – they should:
1. Copy down the raw data – on an overhead of “Data Recorder Sheet”, write in
the data from that class that they collected the previous day and have
students copy the numbers
2. Compute average tail scores for each round (will need calculators) – students
will need help with this – do an example using an overhead of “Round 0
Example”
3. Walk students through this example – you need to start by multiplying the
number of individuals by their tail size for each tail score class, add them up,
and divide by the total number in that round
4. Graph tail size distribution of final tadpoles after Round 3 – students may
need help with this – show how to draw in one sample on an overhead
5. Graph average tail size over time – encourage them to make a line graph
6. Describe how tail size changes with time
7. Reassess their hypothesis
DAY 3
Have students finish the worksheet as many won’t finish on Day 2.
Discuss follow up questions with students as a group. Possible answers are given but
there may be other answers too.
How did the trait of tail size change through the generations?
ANS: tail size should increase over time because tadpoles with bigger tails are
more likely to survive and reproduce
Talk about other possibilities:
Is this what is really happening in the streams? What are some simplifications?
ANS: only one predator, there may be other traits more or equally
important, crayfish is not evolving, etc…
What if crayfish go away?
ANS: there won’t be selection on tail size, will likely see a wider range of
tail sizes after many generations, small tail size is no longer
unfavorable – whether a trait is favorable or unfavorable depends
on the environment
What if another predator comes into the stream?
ANS: if the other predator is very different from a crayfish, there may be
selection on different tadpole traits, or even in the opposite direction as the
selection by crayfish
What if crayfish are such good predators that tadpoles almost never can escape
predation?
ANS: tadpoles would go extinct in those streams with crayfish
Do you think there are other traits of the tadpole that are under selection?
ANS: yes, possibly behavior (hiding), camouflage, size, speed, etc…
Do you think there are traits of the crayfish under selection?
ANS: yes, likely – ability to catch tadpoles, speed, vision, ability to smell
tadpole chemical cues, claw size
Is there any random process in this game?
ANS: the flipping of the coin is the random process – organisms with a
“bad” trait do not always get killed, they can survive and reproduce if they
happen (randomly) to never encounter a crayfish – in this game,
organisms with the “best” trait do always survive and reproduce which is
an over simplification and not very realistic – in the real world, they may be
subject to random events such as a drought or disease and die
Background
Before the Activity
 Before Day 1:

Print out tadpole cards in color and laminate them – I printed 4 cards for tail









scores 0-2 and 9-11 and 12 cards for tail scores 3-8 (however, I did run
out a few times of specific cards so suggest printing more if possible – in a
pinch, have a dry eraser marker and write the needed tail score on an
unused card)
Print out signs in color and laminate them – 2 crayfish signs, 1 of the others
Make photocopies of handouts (Hypothesis and Data Analysis) and Data Sheets
Make overhead of “Game Schematic”
Before Day 2:
Record data in from the game in a spreadsheet, make calculations
Make overhead of data recorder sheet and fill in data for each class
Make overhead of “Round 0 example” to show students how to calculate the
average tail score for each round
Make overheads of “Data Analysis” Handout to help students and show them
example of how to graph if necessary
With the Students
1.
Image Insert Image # or Figure # here, [note position: left justified, centered or right
justified]
Figure 1
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Caption: Figure 1: ___?
Image file name: ___?
Source/Rights: Copyright © ___?
Attachments
Game Schematic
Hypothesis Handout (Day 1)
Data Analysis Handout (Day 2)
Instructions for Game Leader
Data Recorder Sheet
Round 0 Example
Tadpole Cards and Signs
Safety Issues

Troubleshooting Tips
Day 1 can get a little chaotic and loud. Try to stay as organized as possible – having the
students sit back down after the reproduction stage really helped regain a bit of order.
The game works better for larger classes when you start out with 16 tadpoles in Round
0. By the end of Round 3 or even before, if you don’t have enough students, you will
need to have students play the role of 2 or more tadpoles. If they do this, make sure to
have them flip the coin once for each tadpole card they have. Having more tadpoles
than students at the end of the game occurred in nearly all of the 9 classes in which this
game was tested.
If the class is very small, you could start with fewer than 16 tadpoles – for instance you
could use 9 students to start with the tail distribution as below:
Tail
Score
2 (worst)
3
4
5
6
7
8 (best)
Number
0
1
2
3
2
1
0
Investigating Questions
See Day 3 questions.
Assessment
The questions on Day 3 will give you an idea as to whether the students got it. As well,
grading the worksheets will help you to assess the students understanding of the
concepts. I found that many students confused tadpole tail growth over generations for
tadpole tail growth in individual in one lifetime. This might be something to focus on in
discussion also.
Pre-Activity Assessment
Title: ___?
Activity Embedded Assessment
Title: ___?
Post-Activity Assessment
Title: ___?
Activity Extensions
Activity Scaling
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For lower grades, ___?
For upper grades, ___?
Additional Multimedia Support
References
Gendron, Robert P. “The Natural Selection Game”, Indiana University of Pennsylvania.
Accessed November 5, 2008. http://nsm1.nsm.iup.edu/rgendron/LabsDownload.shtml
Holt, Rinehart, and Winston. Life Science. Austin, TX: Harcourt Education Company,
2007.
Photo/Image credits:
Hypothesis handout and Data Analysis handout
Tadpole image: http://www.pwrc.usgs.gov/TADPOLE/tadmorp.htm
Crayfish image: http://www.freewebs.com/siganurme/seapea.htm
Cards
All photos by Katherine Pease
Signs
Reproduction: Photo by Gary Nafis from
http://www.californiaherps.com/frogs/images/pregillaeggsbu308.jpg
Dead Tadpoles: photo by Katherine Pease, photo by Mike Benard from
http://www.mister-toad.com/PacificTreeFrog.html
Survivor Tadpoles: photos by Katherine Pease
Crayfish:
http://www.malibuwatershed.org/2ndLevel/creaturefeature/creature_redsw
ampcrayfish.html
Schematic
Tadpole: http://clean-water.uwex.edu/pubs/clipart/critters.tadpole.htm
Crayfish: http://www.freewebs.com/siganurme/seapea.htm
Other
Redirect URL
[For TE submissions only]
Owner
Katherine Pease, UCLA Science and Engineering of the Environment of Los Angeles,
NSF GK-12
Contributors
This activity has been classroom tested in the 7th grade classrooms at Emerson Middle
School within the Los Angeles Unified School District under the guidance and help of
teachers Elvia Park and Brian Gabrich.
Copyright