A Mini-Lesson

Natural Selection....
a Cumulative Process...
it's in the cards!
or
Natural Selection Among Playing Cards
by Werner G. Heim

Adapted from an article in
The American Biology Teacher, April 2002

EVOLUTION

 SYNOPSIS

A common criticism of natural selection is "how can it produce novel complex useful structures by pure random chance?" Darwin's answer to this "difficulty", (which he actually raised himself), was that selection is NOT a random process, and furthermore, it is cumulative, which he ably explained. Unfortunately, these facts are seldom included in typical classwork on evolution. It should be a required part for every presentation of natural selection.

This lesson provides an elegant, easy way for students to actually compare Darwin's cumulative non-random selection with the non-cumulative version so often erroneously implied. Students working in pairs attempt to produce a full sequence of 13 cards of one suit (ace - to king). This must be done by shuffling the suit of cards for each round, then checking the cards. Half the teams must look for the full sequence each time, and repeat the process until this is accomplished. The other teams start to "build" their sequence by pulling the ace when it first appears as the top card, then adding to the stack whenever the "next" card for the sequence is shuffled to the top. Discussion clearly reveals how the second method mimics Darwinian natural selection, while the first does not.

 CONCEPTS

MATERIALS:
Playing Cards:

Ideally (for teams of 2): 1 deck of cards for every 8 students (4 decks for a class of 32) Acceptable (for teams of 4): 1 deck of cards for every 16 students (2 decks per class of 32)

scratch paper
envelopes (numbered: 1-16 for class of 32)
Background & Instructions (optional, could be handled orally) (pdf, and below)
Discussion Questions (optional; this could be handled orally) (pdf, and below)
Copy of Original Article on which this lesson is based (pdf)
Copy of this lesson (pdf)
FOR PDF VERSIONS OF THESE MATERIALS, FOR EASY DOWNLOADING, CLICK HERE

TIME:
One teaching period (40-50 minutes)

TEACHING PREPARATION & STRATEGY:
1. This is best done in conjunction with your introduction to natural selection. It could probably work as well before students study it, or after. Vary with different classes to see which works best. Let us know your conclusions.

Try introducing this lesson with an engaging STORY , like the one that teacher Rhoda Garcia uses (SEE BELOW)

2. Separate the cards into their 4 suits (all 13 cards for each suit), and place each set of 13 cards into a separate numbered envelope. Be sure you have enough sets for each team (of 2- 4). These sets can be re-used in subsequent periods.
3. Run off copies of instructions and discussion questions if desired (one set per team is fine).
4. Have scratch paper handy.

PROCEDURE:
1. Divide the class into teams (of 2-4 each)
2. Each team has at least a "recorder" and a "player".
3. The Recorder records the number of rounds played (tally mark for each)
4. Player(s): serve as shuffler, card handler, and/or observer.
5. You may introduce the "game" in various ways, depending on their background and experience.

- a. Simply as "an interesting game" .. to be discussed as to its significance afterwards. - b. Announce that this is a "Natural Selection" simulation. - c. Point out that there is often confusion about natural selection being a random process, and many wonder how such a random process could produce useful complex structures in a reasonable time period. - d. Let them read the Background and Instructions, do the activity, then be prepared to discuss the questions in class.

6. Point out that Odd-Numbered teams will follow procedure A, and Even-Numbered teams must do procedure B. When a team achieves the goal (full sequence ace-to-king), the recorder reports the number of rounds taken to do it. One of the players thoroughly shuffles the cards, returns them to the envelope, and hands it in to the teacher. That team goes to work on the questions, preparing for class discussion.

7. About 5-10 minutes after the last B team has turned in its number of rounds played, call a halt to all remaining team activity. Each remaining set of cards is thoroughly shuffled, returned to its envelope, and this is handed in to the teacher. Display the number of rounds taken by each team, and begin to discuss the questions.

8. Above all, it is critical that students come away with a clear understanding that cumulative natural selection (as Darwin postulated) is a primary source for all new characteristics which have arisen since life began. The cumulative aspect of this is critical partly to show how it increases probabilities for increasingly complex or new combinations in relatively short time spans.
The other function of the cumulative feature is that it builds upon already-successful structures. This has also been called "successive selection of adaptive combinations." It's this cumulative feature which is key to its creative potential. Natural selection is often assumed (incorrectly) to be simply an elimination process, removing all the ill-adapted mutations as they appear. However, especially with details of molecular structures and processes being revealed and understood in diverse species, we have a growing body of observations most easily explained by descent with modification: evolution, occurring as a result of cumulative natural selection.

EPILOG AND COMMENTS:
1. It is important that no religious group (or even "creationists", and certainly no students) be ridiculed for their beliefs which maintain that evolution is wrong. Simply make the general true statement that there are many who misunderstand and may misrepresent evolution, and the point of this exercise is to clearly demonstrate what natural selection IS, and what it is NOT, primarily to clear up the widely held misconceptions. If asked where the misconceptions came from, explain that lots of new ideas can be misunderstood, and if someone writes articles presenting a misconception, many people accept it without questioning, and innocently repeat the ideas to others. This is especially true if the misconception seems to strengthen one's deeply held beliefs.

2. For example, you can mention that some may have heard that an organ such as an eye or an enzyme system could not have arisen by pure chance within a reasonable length of time, therefore evolution could not produce such complex structures or processes, much less complete organisms. The premise is correct, but the conclusion is wrong, because the basic assumption is wrong: evolutionary biology does NOT make this claim. Rather, it claims that such structures and processes arose largely by the accumulation of favorable mutations through the process of cumulative natural selection. Mutation is a chance process (within limits); selection is an anti-chance process. As the card game simulation showed, evolution by cumulative selection of favorable mutations (those that contribute to survival) is a relatively rapid process.

3. If you want to take an even closer look at the evolution of the eye, click here for web sites that do that. Note that there are also many web sites which attempt to discredit these evolutionary explanations for eye evolution, but an element common to all is their total disregard for cumulative selection and how this alone increases probabilities profoundly.

TRY THIS ENGAGING INTRODUCTORY STORY
4. Florida teacher Rhoda Garcia has used this lesson very successfully. She precedes her introduction to natural selection with a delightful and engaging story, and has kindly offered to share it with you here. In fact, you might consider using such stories often in you teaching; kids of all ages enjoy a brief and well-told story, especially one witn a mystery twist.

. Rhoda follows the story with the Natural Selection of Playing Cards lesson (next day), and follows that with the showing of a couple of short video clips from the first show in the PBS Evolution series: Darwin's Dangerous Idea (available in the DVD set, or as a single VHS tape for about $20). First she shows segment 11 (an 11' segment about 58' into program), then segment 13 (a 5' segment about 1hr 25' into the program; called segment 132 on the DVD). In that first segment, Ken Miller discusses eye evolution. In the second segment, biologist Ken Miller talks about his book Finding Darwin's God and his belief that evolution and religion are compatible (he is a practicing Catholic). Miller is also co-author of the popular high school textbook, Biology. Teacher Garcia confirms the importance of the lesson, and says that the video clips help to round it out , answers some questions, and stimulates further discussion. Be sure to get the free Teachers Guide to the PBS series, and the several other excellent tapes, especially the Videos for Students, with 7 6' video clips to get discussion going (VHS tape, or direct viewing online).

EXTENSIONS & VARIATIONS:
1. Further evidence that species are the product of long term accumulated modifications can be found in the existence of pseudogenes. An excellent series of lessons available on this site enables students to experience the existence of pseudogenes by exploring the production of vitamin C in selected organisms and how this points to common ancestry. Take a look at the Pseudogenes Suite . The existence of pseudogenes also suggests that natural selection provides a more parsimonious explanation for the origin of species than does "intelligent design", a fairly recent version of what is essentially "scientific creationism", both of which are pseudoscience.

2. In conjunction with this lesson, provide your students with a natural selection simulation experience which takes them through at least a few generations of selection, e.g. "The Chips Are Down" natural selection lesson, or "Natural Selection of Bean Hunters" .

REFERENCES: In addition to those listed in the article by Dr. Heim:
Dawkins, Richard. 1996. Climbing Mount Improbable. New York: Norton & Co. See especially chapter 5.
A Critical Review of Behe's Darwin's Black Box and the flaws in the author's "irreducible complexity" ideas. Includes examples of complex structures and molecular processes whose probable evolutionary sequence by cumulative selection have been figured out.

 ATTRIBUTION

Some of the ideas in this lesson may have been adapted from earlier, unacknowledged sources without our knowledge. If the reader believes this to be the case, please let us know, and appropriate corrections will be made. Thanks.

Original article: "Natural Selection Among Playing Cards" by Werner G. Heim, in the April 2002 issue of The American Biology Teacher, vol. 64, no. 4, pages 276-278. Dr. Heim is Professor Emeritus of Biology, Department of Biology, The Colorado College, 14 East Cache La Poudre, Colorado Springs, Colorado 80903-3294; E-mail: wheim@coloradocollege.edu

Lesson adapted for ENSIweb lesson by Larry Flammer, September 2002, with kind permission of NABT and the author.

Some updating and correcting: 6 April 2007.

BACKGROUND: When studying natural selection, the question often arises "how can pure chance create new complex structures or processes, much less new species?" Implied here is that natural selection is a process of pure chance, which is a common misconception; selection is not a matter of chance. Furthermore, natural selection does not say that all parts of a complex system must come together all at once. Natural selection is a stepwise constructive process which selectively builds new functional complex systems piece by piece, often just modifying previous systems to perform new functions. This truly creative ability of natural selection is often unappreciated or even misunderstood. The purpose of this lesson is for you to experience the effectiveness of cumulative natural selection, both in its creative potential, and in its increased efficiency, as reflected in how it increases the probability of complex systems to form.

PROCEDURE: Working in teams of 2-4 (as directed by your teacher), you will work with one suit of 13 cards (ace to king), shuffling the suit thoroughly for each round, and attempting to produce a particular sequence, following the rules assigned to your team, as follows:

FOR THE "A" TEAM, Odd-numbered sets:
1. Shuffle the cards thoroughly.

2. The recorder keeps track of the number of rounds played, increasing the count by one each time after the shuffling is completed.

3. Examine the cards. Are they in the order ace, 2, 3 ... jack, queen, king?
A. If so, inform the instructor of the recorder's count, i. e. of how many rounds have been played. Then stop as the goal has been reached.

B. If not, play another round, i. e. repeat steps 1., 2. and 3.

FOR THE "B" TEAM, Even-numbered sets:
1. Shuffle the cards thoroughly.

2. The recorder keeps track of the number of rounds played, increasing the count by one each time after the shuffling is completed.

3. Examine the cards. Is the top card an ace? If so, use it to start an "organism" stack. After this stack has been started ask whether the top card is the next one needed to construct the "organism." If, for example, the top (and only) card in the "organism" stack is the ace, then the next card needed is the two. Or if the top card in the "organism" stack is a seven, the next card needed is the eight, etc.
A. If the top card is the next card needed for the construction of the "organism," place it face up on the "organism" stack. Then repeat steps 1., 2. and 3.
B. If the top card is not the next card needed for the construction of the "organism," do not place any card on the "organism" stack. Instead repeat steps 1., 2., and 3.

4. When all the cards are in the organism stack (with the king on top), inform the teacher of the recorder's count, i.e. of how many rounds have been played. Then stop as the goal has been reached.

DISCUSSION: When you have achieved the target sequence (or when your teacher says to stop trying), return the cards to their envelope, and work on answering the discussion questions on a separate sheet:

When you have achieved the target sequence (or when your teacher says to stop trying), return the cards to their envelope, and work on answering the following questions. Be prepared to participate in class discussion of these questions.

1. In what ways is shuffling the equivalent of genetic mutations?

In what ways is it not?

Does the model (card "game") distinguish between phenotype and genotype?

2. What is the one, critical respect in which the actions of the odd- and even-numbered teams differed?

What is the biological equivalent of this difference?

3. What, in the game, represented selection?

4. Why, in the game, was selection cumulative?

5. What was the average number of observed generations needed to evolve the organism by the even-numbered teams?

How does this figure compare to the calculated average number of generations? (Hint: On the average, in each round, the ace has a 1:13 chance of coming up, the "2" has a 1:12 chance, etc. The sum of the numbers from 1 to 13 is 91)

6. What was the average number of observed generations needed to evolve the organism by the odd-numbered teams?

Do we have the data to answer this question?

What would be the calculated number of generations? (Hint: We need to have the ace show up first, with a probability of 1/13, then the "2," with a probability of 1/12 ... to the king with a probability of 1/1. 1/13 X 1/12 X 1/11 ... 1/1 is approximately 1.6X10^-10. 1/1.6X10^-10 is about 6.2X10^9. Shortcut: 13! = 6,227,020,800.)

7. How many times faster is the evolution of our model organism with versus without cumulative selection among the mutations?

8. What new understanding has this lesson taught you?