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The Beaks of the Finches

Cherry Sprague



Type of entry:

  • class activity

Type of activity:

  • hands-on activity
  • simulation
  • inquiry lab

Target audience:

  • AP Biology


Background Information

Shortly after Peter Grant published Natural Selection and Darwin's Finches, (Scientific American, Oct. 1991) he accepted an invitation to speak to my classes. The students read his article prior to his talk. His lecture included slides and data of his on-going research work with the finches of the Galapagos. Last summer's reading of The Beak of the Finch by Jonathan Weiner brought a greater insight into the Grants' work, and created the link of the article's pictures of beaks being matched to tools. This led to a revision of labs on natural selection and population genetics for the AP biology classes. The ideas created the following lab simulation(s) and the labs received an enthusiastic and critical review by the students in AP biology.

In this simulation students become birds and are given "beak-types". After completing the activity, students will relate results to adaptations and natural selection. Extensions of the simulation allow for comparative results and include population genetics.

Information for the Teacher
It is suggested strongly and enthusiastically that teachers read the article and the book prior to doing the lab. At the end of the procedure, there are additional notes for the teachers' perusal and consideration.

The problems being studied can be stated in different ways. Here are a few:

1. What is the relationship between beaks and seed-gathering?

2. Which beak(s) are the favored type(s)?

3. How does natural selection contribute to adaptation(s)?

4. Are the beaks at the end of the simulation the best-adapted ones?

Required of Students:

  • Complete reading chapter in text that presents evolution by natural selection
  • Read Natural Selection and Darwin's Finches
  • Complete 1/2 page long responses that analyze or interpret the following three quotes.

    Stephen J. Gould, " Ideal design is a lousy argument for evolution...Odd arrangements and funny solutions are proof of evolution."

    Richard C. Lewontin, " The relationship between adaptation and natural selection does not go both ways. Whereas greater relative adaptation leads to natural selection, natural selection does not necessarily lead to greater adaptation."

    Neil Campbell, "Of all the agents of microevolution that change the gene pool, only selection is likely to be adaptive."

Although the students' responses have been shared and assessed in class discussions prior to this lab, the results of the lab will provide remarkable illustrations relative to the quotes, and provide a springboard for more critical thoughts and reflections.

Preparation Time:
One hour to find tools, create a key of tools and buy two bags of different seeds.

Class Time Needed:
Double period lab(88 minutes) and next day's lecture period(44 minutes)


Activity: The Beaks of the Finches

Materials:

  • 10-12 petri dishes
  • 5-6 large Syracuse dishes
  • Two bags of seed types such as, black sunflower seeds and popcorn
  • 12 different tool types-wire cutters, wire stripper, blunt-end pliers, sharp-end pliers, clothes pin, cable attacher, pruning shearers, vise-pliers, long-handled vise, another wire stripper/cutter combo tool, needle-nosed pliers and wire clip

Procedure:

1. Place the numbered tools around the room and allow students to note descriptions. Recommend the students draw these and/or write detailed descriptions. Time 15 minutes.

2. Ask students to evaluate the potential value of the tools to pick up seeds singularly and place in the petri dish (crop).(1)

3. Depending on the class size the students eliminate the excess tool(s). For class discussion, before voting, students discuss reasons to eliminate particular tools, while displaying each tool. Once a tool has been nominated to be eliminated, the discussion is expanded to hear the more varied reasons and arguments. The students vote to decide which tool(s) to eliminate(2). There must be at least one more tool than the number of groups in the class. Time 10 minutes.

4 Pairs(or trios) of students are assigned a tool and allowed a few minutes to practice picking up seeds and moving them to the petri dish. One or two-handed holding of the tools is permitted; decide which during the practice minutes.

5. Place hundreds of seeds into each large Syracuse dish(3). Have two sets (two tool groups) of students work from each Syracuse dish.

6. Each student must work the tool. Each student repeats the trial two or three times depending on size of group. Six trials are averaged for a final value. Each tool is to handle one seed at a time. A seed only counts when it drops and stays in the petri dish. After each twenty second feeding period, all seeds are returned to the Syracuse dish.

7. All the students work during the same time period. Teacher starts and ends time. Twenty seconds is the time period. The critical survival value was set at an average of thirty seeds per 20 seconds.

8. Values less than an average 30 seeds/20 seconds were eliminated after the first round. Values were recorded on the board. Those tools and students which were eliminated are asked to monitor the survivors, insure that the rules are followed by those remaining, record the class data, and to observations about what occurs ( strategies) in the more competitive rounds.

9. The surviving tools and sets of students move into four feeding groups at one large Syracuse dish. The number of seeds in the dish remains the same.

10. Steps 6 and 7 are repeated in the larger groups. Data are collected again. Determine the average # seeds/20 seconds from six trials again. The survival value does not change, just the level of competition for the resources.

11. The last and final round of competition places all the tools and sets of students around the same Syracuse dish. Find a table that allows equal access for all feeding groups(sets) in this final round.

12. At the end of this final round, collect the data again. Have students who have been observing write down their observations. Have students who were winners write down any reflections about their competition and survival with the tool.

13. The class results should be discussed as soon as possible so that observations and ideas are shared about this complete round. (4)

14. If time is limited, then this could end the simulation. If time is available, repeat the entire process using another seed type and compare final results.

15. Another variation is to use colored (popcorn) seeds to learn about the survival value of the seeds. In doing a version that looks at the seeds' survival, one can build the activity as a population genetics simulation of Hardy-Weinberg by using three seed colors derived from two codominant alleles giving the three phenotypes. Also, important here is the background of the table tops and the degree of camouflage offered the various seed types.

Notes about Procedure

(1) Some students during this activity may ask about the seed type. If asked, answer by placing same seeds in a dish. If not, this will quickly become a point of discussion in the next step.

(2) Some nominated tools will remain in the simulation and some students will be disappointed with the assigned tool. This creates some of the more interesting competition.

(3) Measure the seeds by volume, rather than counting. Covering the entire dish with one layer of seeds is adequate.

(4)Focus comments to Darwin's points about natural selection, but avoid any teacher-stated conclusions. The lab reports will be more interesting reading.


Methods of Evaluation (Both Suggested)

  • Post-discussion by groups and by class
  • Individual lab reports.


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