Name
Period
Date
Lab: Natural Selection with Teddy Grahams
PURPOSE:
Model the process of Natural Selection using Teddy Grahams.
STORY:
Welcome to the land of Teddy Grahams. These bears are a peaceful, herbivorous species that has
long enjoyed life without a predator. Their population size remains around 12 bears. They are limited by
the number of caves in which to hibernate. The bears live in a habitat with lots of shrubs.
There are two general behaviors of teddy grahams. Type A (Happy) bears run around with their
hands up. This was an adaptation for preventing the growth of a deadly mold under their armpits. Type B
(Sad) bears, much more rare than type A bears, run around with their hands down. For the past few
hundred years, the mold has no longer been a problem, so neither type of behavior is better than the other,
therefore this variation is neutral.
The hands-down (sad) behavior is a genetic trait caused by a dominant gene H. Therefore, sad
bears are either HH or Hh. Happy bears are hh.
Recently, a terrible thing has occurred. A new “bear-eating monster” (that’s you!) has emerged.
The predator has developed a taste for teddy grahams. The Happy Bears are easy to see, with their hands
rising high above the shrubs and bushes. Therefore they make easy prey for the predator. The Sad Bears,
however, are nicely hidden and quite safe from the predator. Fortunately, the monster can only manage to
eat four bears a year.
PREDICTION:
What do you predict will happen to the population of the bears over time? EXPLAIN YOUR REASONING!
PROCEDURE:
When the predator first arrives, there are 12 bears: 11 happy bears and only one sad bear. The sad
bear is heterozygous (Hh).
1. Obtain a population of bears.
2. From your population, count out 11 happy bears and 1 sad bear. These 12 will be your first
generation.
3. The predator eats four bears a year. So remove four of the bears (DON’T EAT YET…put them
back with the rest of your bear supply!) REMEMBER: The predator can only catch hands-up
bears.
4. Now it is breeding season. Put the remaining 8 bears from the original population (not the extra)
into a plastic baggy and pull them out two by two. These are their breeding pairs. Each pair will
produce one new bear cub. The phenotype of the cub will depend on the genotypes of the
parents. Use a dice and these rules to determine the genotype and phenotype of each bear cub:
a. Two Happy Bears
hh x hh = all Happy Bears (hh)
b. One Happy Bear and one Sad Bear
HH x hh = all Sad Bears (Hh)
Hh x hh = 50% Sad Bears (Hh) Roll a 1, 2, or 3
50% Happy Bears (hh) Roll a 4, 5, or 6
c. Two Sad Bears
HH x HH = all Sad Bears (HH)*
Mark any bears that are homozygous dominant (HH) by biting off an ear or a toe,
then you know the others are heterozygous.
HH x Hh = 50% Sad Bears (HH) Roll a 1, 2, or 3
50% Sad Bears (Hh) Roll a 4, 5, or 6
Hh x Hh = 25% Sad Bears (HH) Roll a 1
50% Sad Bears (Hh) Roll a 2, 3, 4, or 5
25% Happy Bears (hh) Roll a 6
5. After the bears have reproduced, record the numbers of each in the data table.
6. Repeat steps for the next 9 generations. Record the numbers of each type of bear in the table.
7. Create an appropriate graph of the data by plotting the total number of bears for each
generation, placing time on the x-axis. (You won’t graph the numbers recorded for “After
Predator Eats.”) Use two colors and provide a legend to distinguish between Happy and Sad
Bears.
Data:
Generation 1
After Predator Eats
Generation 2
After Predator Eats
Generation 3
After Predator Eats
Generation 4
After Predator Eats
Generation 5
After Predator Eats
Generation 6
After Predator Eats
Generation 7
After Predator Eats
Generation 8
After Predator Eats
Generation 9
After Predator Eats
Generation 10
Happy Bears
Sad Bears
Population Size
11
1
12
7
1
8
12
8
12
8
12
8
12
8
12
8
12
8
12
8
12
8
12
ANALYSIS:
1. What happened to the population of each type of bear over time?
2. How does this compare with your prediction?
3. Identify the 4 principles of Darwin’s natural selection AND DESCRIBE how this experiment met
each of the conditions. (refer to notes if needed)
a.
b.
c.
d.
4. Did natural selection occur? What is your evidence?
5. Which bear did natural selection select against?
6. Which bear did natural selection select for?
7. How will natural selection of Teddy Grahams affect the predator of Teddy Grahams?
8. Can there ever be Happy Bears again? Why or why not?
9. Look up the term “carrying capacity.” Define AND identify the carrying capacity in this
simulation.
10. Look up the term “limiting factor.” Define AND identify the limiting factor in this simulation.
11. This activity was designed to model the process of life and death that is involved in natural
selection.
a. Do you feel that this model was successful/helpful or unsuccessful? EXPLAIN!
b. What improvements can be made?
Describe the FIVE FINGERS of evolution.
1) How many new bears did you get for each generation?
 Generation 2 Answers will vary.
 Generation 3 Answers will vary.
 Generation 4 Answers will vary.
2) What happened to the percentage of each type of bear over time?
a. Happy? Decreased over time
b. Sad? Increased over time
3) How does this compare with your hypothesis? Answers will vary.
4) List the four conditions necessary for natural selection to occur.
a. Every species contains genetic variation
b. Because organisms produce more offspring than can survive, living things face a constant struggle for
existence
c. Only some individuals survive and reproduce
d. Because each generation consists of the offspring of individuals that successfully reproduced, natural
selection results in genetic change.
5) Describe how this model met each of the four conditions.
a. There are happy and sad bears in the same species of bear.
b. The bears are preyed upon by the bear-eating monster. There are more bears than monsters.
c. The sad bears are better adapted to survive being caught by the bear-eating monster because it is
sneakier, harder to catch and taste bitter.
d. As each generation passes, we can see more sad bears in the population than happy bears.
6) Explain which trait is not favorable.
The happy bear trait is not favorable because they do not possess adaptations that allow them to avoid
the bear-eating monster (predator)
7) Which phenotype is reduced in the population? The happy bear phenotype
8) Explain what would happen if the selection pressure changed and the happy bear was selected for.
The number of sad bears would decrease in the population.
9) Did natural selection occur? What is your evidence?
Yes. Natural selection did occur because the bear with the advantageous trait (sad bear) were more
successfully surviving, reproducing and passing on its favorable traits to its offspring at each successive
generation. Meanwhile the number of happy bears decrease in the population.
10) What was the resulting adaptation from this natural selection?
No, the organisms that had the best adaptations for survival were the ones remaining in the habitat. The
adaptations that were more successful in this population were being sneaky, having a bitter taste, and
being harder to catch (faster?)
11) What was the force driving the natural selection?
The presence of a predator (the student)