humor:teddy graham evolution

["Jenny Lando" <jenny@amnh.org>]

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Teddy Graham Evolution

While the study of biology and life science encompasses many confusing and
difficult topics, none seems to be as difficult as natural selection.
Students often think that animals consciously adapt to their environment:
the peppered moth changing color, the giraffe stretching its neck, and the
polar bear turning white so it blends in with the surrounding snow are
common misconceptions. Once ingrained in the student's thinking, these
mistaken concepts are often difficult to correct. While we agree that there
is no 'magic potion' that will guarantee that students understand natural
selection, we have developed an activity that models the theory, directly
involves the students as the selecting agent, and incorporates a strong
motivating force: food. (Remember, when working with food, be sure no
chemicals are around and table tops are clean.)

Teddy Grahams are little graham crackers that look like bears. Each box
contains bears with two traits: one with their hands up and one with their
hands down. One trait can be designated as adaptive to the environment, and
the other can be considered non-adaptive. The number of boxes you use
depends on your class size. The total number of crackers can be considered
your population gene pool. How simple or complicated you get depends
entirely upon your own goals for the class. Here are two versions of the
same activity. The first, "Natural Selection with Teddy Grahams," can be
used in any basic life science or biology class. The goal is for students to
understand the basic concept of natural selection and to have them explain
and graph what happens to two populations of bears over time. The second
activity, "Evolution with Teddy Grahams," incorporates the same ideas from
the first activity with the addition of using formulas from Hardy-Weinberg
equilibrium for calculating the frequencies of the dominant and recessive
genes. The students can calculate the specific frequencies of each genotype
over successive generations. These results can lead to a variety of
questions regarding the nature of dominance and recessive traits in
organisms. You can also discuss why a recessive gene with an unfavorable
trait remains in the population. Ultimately, we would like the students to
understand that, in order for evolution to occur, there must be a change,
over time, of the gene frequency of the organisms.

Natural Selection with Teddy Grahams

Divide the students into groups of two and have them read the introductory
story that describes the environmental conditions affecting favorable and
unfavorable traits. After the story is read, have students follow the
prescribed procedure and predict the outcome of each population of bears.
You are a bear-eating monster. There are two kinds of bears: happy bears and
sad bears. You can tell the difference between them by the way they hold
their hands. 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, are sneaky, and hard to catch. Because of this, 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 the last
year.

First, obtain a population of bears, and have your students record the
number of happy bears, sad bears, and the total population for each
generation in a data table. Second, eat three happy bears. (If you do not
have three happy bears, then eat the difference in sad bears.) Obtain a new
generation from the teacher, repeat the steps for two generations, and graph
each population result. Have students write a paragraph explaining what
happened to each population of bears and why. Have them contrast the
conclusions with their original predictions.

Evolution with Teddy Grahams

Use the same story and procedure as in natural selection scenario, but add
the following information. Since the happy trait is recessive, the happy
bears are homozygous recessive. In addition, because the sad trait is
dominant, the sad bears are either homozygous or heterozygous dominant.
Using the two formulas, calculate the gene frequencies for both the dominant
and recessive genes and the genotypes that are represented in the population
(see Figure 1). Begin with calculating the percentage of homozygous
recessive organisms and then use this number for the remaining calculations.
We suggest that you ask your students the following questions:
1. Explain which trait is not favorable.
2. Which phenotype is reduced in the population?
3. What specifically happens to the genotypic frequencies from generation
one to generation four?
4. What occurs when there is a change over time of the genotypic
frequencies?
5. Explain what would happen if the selection pressure changed and the
recessive gene was selected for.
6. What would happen if it were better to be heterozygous (Aa)? Will there
be homozygous bears? Explain.
7. What happens to the recessive (a) gene over successive generations?
8. Explain why the recessive gene (a) does not disappear from the
population.
We have found these two activities to be an effective means for enhancing
students' understanding of Darwin's Theory. Because they are directly
involved with being the actual selective agent, students begin to
conceptualize this theory and realize that environmental and genetic factors
are influential in determining the survival of organisms. Students
eventually form the conceptual link between an organism's appearance and
behavior, and the idea that genetic material determines hose traits.
Ideally, they replace previous LaMarckian thoughts with new ones that
reflect the current understanding of evolution and natural selection.
Students come to understand that genetics determine the survival of an
organism, but these organisms cannot actively change to fit their
surrounding environment. The motivating factor of food appears to enhance
the success of the activity. Any edible product that can represent the two
traits will work. Other suggestions are for the red and green Christmas M&Ms
and Ritz Pieces crackers. (Put the M&Ms in the freezer until needed. Be sure
to use a classroom where toxic chemicals are not used if students are to eat
their 'prey.') We have been successful in using these activities from middle
school life science to Advanced Placement biology, and we believe they would
be equally effective with upper elementary children.



Jenny Lando
Assistant Coordinator/Paleontology of Dinosaurs
Moveable Museum
Education Department:AMNH
Central Park West @ 79th Street
NYC NY 10024
212-769-5189
212-769-5329 (fax)