Teddy Graham Lab:
CLASS SET: DO NOT WRITE ON
Read all INFORMATION below as you complete the Lab:
Natural selection is the process in which organisms that are best adapted to a set of
environmental conditions will survive long enough to reproduce. By reproducing, these
organisms will pass the successful genetic information to the next generation. Those organisms
that are not as well adapted are more likely to die before they have a chance to pass on their
genes. The overall composition of the population will change as the survivors with the more
beneficial genes or adaptations produce more offspring.
As you read through the Lab you will be given a series of assignments that must be done on your
paper to be sure you are reading as you are told to do so. I have learned that throughout the year
that my students are not reading, so those of you who do read and complete the require
assignments will receive a higher grade. Do not tell anyone in your group what is going on, just
do all the assignments correctly and you will get full credit for the lab.
Natural selection is sometimes referred to as “survival of the fittest”. (Write the phrase “survival
of the fittest” above your name on the student date sheet) The organisms that are best adapted
will be the parents of the next generation. It is important to note that the organisms do not adapt
to their environment. (Draw a flower on the back bottom right hand corner of your student data
sheet, in the square provided) For example, in a desert setting, narrow leafed plants survive at a
higher rate than broad leafed plants. The narrow leafed plant is better adapted to the dry
environment because it does not lose as much water through its leaves. The broad leafed plant
would lose too much water and die before reproducing. The broad leafed plant can’t adapt to the
desert environment. The narrow leafed plants DO NOT “become adapted”, rather they possess
adaptations that make them better suited for survival. (Draw a cactus on the back bottom left
hand corner of your student data sheet, in the square provided) An adaptation, then is an
inherited trait that gives an organism possessing that trait a reproductive advantage. When
natural selection is occurring, those organisms that possess the adaptation survive at a higher rate
than those that do not possess the adaptation.
PURPOSE
In this activity, you will simulate the events of natural selection. The population experiencing
natural selection in this simulation is a population of bears. There are two kinds of bears – happy
and sad bears. Happy bears hold their hands high in the air and sad bears hold their hands down
low. Happy bears taste sweet and are easy to catch. Sad bears taste bitter and are sneaky and
hard to catch.
MATERIALS
Teddy Grahams
Paper towels or napkins
Calculators
PROCEDURE
1. Read the follow directions carefully:
Evolution
You are a bear-eating monster. You like happy-bears because they taste sweet and are easy
to catch. Sad bears are not part of your diet because they are bitter, sneaky, and impossible
to catch. For this reason, you eat only happy bears. New bears are born every ‘year’ (during
hibernation) and the birth rate is one new bear for every old bear left from last year.
2. Form a hypothesis about what you expect to happen to the number of Happy and
Sad bears over time. Write your hypothesis in the space provided on the student data
sheet.
3. Establish your generation 1 population of bears by having one partner reach in the box,
without looking, and randomly select 20 bears.
4. Place the 20 bears on a clean paper towel. Count how many happy and sad bears are
present. Record your numbers for generation 1 on the student data sheet (Table 1)
5. Simulate predation by choosing 5 happy bears from the population and eating them. If
you only have 3 or 4 happy bears, eat them first and then consume enough sad bears to
meet your quota. For example, if you have only 3 happy bear, eat them and 2 sad bears.
Remember – you prefer the happy bears.
6. To simulate reproduction in the population, close your eyes, reach into the bag, and
choose 5 bears to add to your paper towel. This should bring the total number of bears to
20
7. Record the number of happy and sad bears that are now present in generation 2 in your
table.
8. The other partners should now take a turn at being the predator. The predator should eat
5 happy bears from the population. If there are not 5 happy bears, follow the procedure
in step 5.
9. Simulate reproduction in the population by repeating step 6. Count the numbers of each
type of bear in the replenished population and record the data for generation three in your
table.
10. Repeat steps 8 and 9 one more time for a total of 4 generations of data.
11. Determine the percentage of Happy and Sad bears for each generation and record the
percentages in Table 2. To determine the percentage take the number of happy or sad
bears and divide by the total number of bears for that generation and multiply the answer
by 100. For example, if there were 12 Sad bears and 4 Happy bears in a generation, then
there were 16 bears total. To obtain the percentage of Sad bears you would divide 12 by
16 and then multiply the answer by 100. To obtain the percentage of Happy bears you
would divide 4 by 16 and then multiply the answer by 100.
12. Graph what happens to the bear population over time. Graph the percentage data for both
the Happy and Sad bears on the same graph. Put the Percentage as the dependent variable
on the y-axis (every other line 10% increments) and the generations as the independent
variable on the x-axis (every 3rd line a generation). Make a line graph, Happy bears in
blue and sad bears in red. (Make sure to include a key and label you graph)
13. Answer the questions after completing the graph.
Evolution
STUDENT DATA SHEET
NATURAL SELECTION
WITH TEDDY GRAHAMS
NAME________________________
PERIOD: ____ DATE_________
HYPOTHESIS
______________________________________________________________________________
__________________________________________________________________
DATA
Table 1. The number of bears for each generation
Generation
Number of
Number of
Happy bears
Sad bears
1
2
3
4
Total Population
of Bears
Table 2. The percentage of bears for each generation
Generation
Percentage of Happy bears
Percentage of Sad bears
1
2
3
4
Evolution
QUESTIONS
1. What was the adaptation of the variation that gave individual an advantage over other in
the population?
2. Explain why his adaptation was an advantage.
3. What was the selective pressure (i.e. types of selection) (disruptive, stabilizing or
directional) that created the advantage of one version of the trait compared to the other
version of the trait and why?
4. What happened to the percentage of each type of bear over time?
a) Happy?
b) Sad?
5. How does this compare with your hypothesis?
Evolution