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Darwin's Finches and Natural Selection



Co Authors:

Cheryl A. Heinz
Department of Biology
Benedictine University
cheinz@ben.edu

Eric Ribbens
Department of Biological Sciences
Western Illinois University
E-Ribbens@wiu.edu

Abstract:

In this "clicker case," students learn about natural selection through the research of Peter and Rosemary Grant and colleagues on the finches of the Galapagos Islands. Students are presented with data in the form of graphs and asked to determine what is happening to a population of finches as the changing environment produces changes in the shape of the finches' beaks. This case is suitable for any size course in introductory biology, ecology, or evolution, and does not require any pre-requisite knowledge of evolution or natural selection. The case consists of a PowerPoint presentation (~4.5MB) punctuated by questions that students answer in class using "clickers." It can be adapted for use without these technologies.

Objectives:
  • Understand that natural selection is a mechanism of evolution that requires heritable variation and differential survival and/or reproduction.
  • Realize that evolution by natural selection can be observed within short periods of time.
  • Develop basic graph reading skills.
  • (Optional Epilogue): Realize that the advantageousness of a trait changes as the selective environment changes.
Keywords: Natural selection; finch; finches; birds; beak depth; beak size; beak shape; Galapagos Islands; microevolution; evolution; graph reading; Rosemary Grant; Peter Grant; Charles Darwin
Topical Area: Scientific method
Educational Level: High school, Undergraduate lower division
Formats: PDF, PowerPoint
Type/Method: Clicker, Interrupted
Language: English
Subject Headings: Evolutionary Biology   Ecology   Biology (General)   Botany / Plant Science  
Date Posted: 09/16/08
Date Modified:
Copyright: Copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.

Teaching Notes


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Answer Key


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Supplemental Materials


This case has an optional epilogue that extends the case (the first item listed below). It is available in the form of a separate PowerPoint presentation (~340KB). It describes evolutionary dynamics over a slightly larger time scale on the islands, and would be appropriate for use in more advanced classes that consider evolutionary dynamics in more depth.

We also list below other supplemental materials that could be used with this case.

  Epilogue to Darwin's Finches
  Click-and-Learn: Sorting Finch Species hhmi/
This activity tests students' ability to distinguish between two species of finches living on the island of Daphne Major based on how they sound and look. Download the accompanying PDF worksheet for students to complete as they go through the Click-and-Learn. Produced by HHMI BioInteractive.
  Data Point Activity: Effects of Natural Selection on Finch Beak Size hhmi/
This graph (from an article by Rosemary and Peter Grant) shows the distribution of beak depths in the breeding population of medium ground finches on the island of Daphne Major in 1976 and of the survivors of the 1977 drought. Download the educator guide PDF, which includes questions to guide a class discussion on the graph characteristics and what the data show. The finch presentation PowerPoint is an alternative approach to teaching this data point. Use this presentation to guide students through discussing the components of the graph. Produced by HHMI BioInteractive.
  Evolution in Action: Data Analysis hhmi/
These two student activities are based on morphological measurements provided by the Grants from a sample of 100 medium ground finches on the island of Daphne Major. (The complete data set is available in the Excel spreadsheet available at this site.) In one activity, students are guided through the analysis of the Grants’ data by constructing and interpreting graphs, and calculating and interpreting descriptive statistics. The second activity provides an example of how the data set can be analyzed using statistical tests, in particular the Student’s t-Test for independent samples, to help draw conclusions about the role of natural selection on morphological traits based on measurements.
  Beaks As Tools: Selective Advantage in Changing Environments hhmi/
The Grants were able to track the evolution of beak size twice in an amazingly short period of time due to two major droughts that occurred in the 1970s and 1980s. This activity simulates the food availability during these droughts and demonstrates how rapidly natural selection can act when the environment changes. Students use two different types of tools to represent different beak types to see which is best adapted to collect and "eat" seeds of different sizes. Students collect and analyze data and draw conclusions about traits that offer a selective advantage under different environmental conditions.
  Natural Selection and the Evolution of Darwin's Finches hhmi/
This lesson supports viewing of the short film "The Beak of the Finch" (linked to from under the Video tab for this case). Students watch segments of the film and then engage in discussion, make predictions, create mathematical models of data, and use multiple sources and types of evidence to develop arguments for the evolution of Darwin's finches.

Videos

The following video(s) are recommended for use in association with this case study.

  The Origin of Species: The Beak of the Finch hhmi/
This short film discusses the work of Rosemary and Peter Grant to document the evolution of the famous Galápagos finches by tracking changes in body traits directly tied to survival, such as beak length, and identified behavioral characteristics that prevent different species from breeding with one another. Their pioneering studies have revealed clues as to how 13 distinct finch species arose from a single ancestral population that migrated from the mainland 2 to 3 million years ago. Running time: 15:54 min. Produced by: HHMI BioInteractive.

  Beak of the Finch Film With Quiz hhmi/
An interactive version of the above film, including pause points and quiz questions.




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