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The Galapagos Finches provides a context in which students investigate microevolution on a Galapagos island. The scenario provides a simplified version of the data and observations collected on the Galapagos island Daphne Major by Peter and Rosemary Grant. This scenario focuses on the drought of 1977 when the finch population dropped by three-fourths. Students are asked to explain why so many finches are dying, and what enables the surviving finches to survive.
Learning About Evolution
Evolution by natural selection is a topic that many students find difficult, and many students maintain alternative conceptions about this topic even after instruction. For example, the scientific model holds that traits become established in a population as the proportion of individuals possessing these traits increases with each subsequent generation. In contrast, some students believe that each individual offspring in a new generation is slightly different on a particular feature than the parents generation. For example, when explaining how Cheetahs evolved to run about 60 miles an hour from ancestors that could only run about 20 miles an hour, some students explain that each individual Cheetah is born able to run slightly faster than its parents, until eventually, over many generations the Cheetahs evolved to run 60 miles an hour.
The Galapagos Finches is designed to help students develop a sound conception of evolution by natural selection, in addition to developing inquiry skills and a general understanding of the nature of scientific argumentation. The scenario emphasizes constructing explanations that are couched in the principles of evolution by natural selection, explicitly prompting students to identify pressures, variability and advantageous traits in their explanations.
Investigating Natural Selection
In the software, students investigate microevolution in a simulation of a Galapagos island ecosystem, based on a twenty year study of finches on the island Daphne Major. Students are asked to explain why some of the finches are surviving while others are dying during a crisis period in 1977, and the implications for future generations. The computer environment provides tools that enable students to gather data, and facilities to help students interpret data and consolidate their explanations. Students may take quantitative measurements of environmental factors (e.g., amount of rainfall), and of the distribution of various structural characteristics of the birds (e.g., weight, beak length). Students can also examine field notes collected about the plants, animals, and environment of the island. The field notes provide students with important behavioral information.
The Galapagos Finches makes explicit and continually reinforces strategies for reasoning about biological data, such as looking for structural and behavioral differences. This is achieved by having data requests made through a question-based interface where students construct questions to retrieve data. These questions reflect the type of questions biologists can ask of their data when they investigate natural selection events.
An example question is: "Are there changes between time periods in the variation of structural traits (see Figure 1)." Figure 2 shows the graph that results from this query, and observations of an individual finch and its behavior that can be made as follow-up observations to the original question concerning variation in structural characteristics.
The Investigation Journal (Explanation Constructor)
The investigation environment is coupled with an investigation journal that enables students to construct an explanation, by typing in free text. The journal structures students explanation by providing a template that consists of the theoretical building blocks of an evolutionary explanation, e.g., environmental pressure, organism affected by pressure, variation of traits in the organism, and selective advantage of a variation. The investigation journal enables and encourages students to directly support the claims they make in their explanations with evidence collected in the investigation environment.
Scientific Explanations in the Classroom
The current scientific explanation is that the finches are dying as a result of lack of food caused by a drought. Normally, the birds' diet consists of small, soft seeds, but due to a prolonged drought those seeds are not readily available, and the seeds that are more available are large, hard, thorny seeds. Finches that have a slightly deeper beak are able to eat the available, larger seeds, and thus are better able to survive the drought. However, students have the opportunity to consider and pursue a range of valid hypotheses. For example, some students conjecture that the finches are dying due to an increase in predation, and they observe owl data in order to investigate this idea. Other students relate the finches' demise to lack of food resources, but speculate that leg size is the selected trait. They can compare graphs of the variation in leg size of live and dead finches and see if there are marked differences in the trends between the two populations, and examine field notes to discern whether leg size affects the foraging ability of the finches. We want students to debate which test is the most sensible to perform, and what constitutes good data.
We interleave the computer activities with whole class discussions where students describe their current questions, hypotheses and investigation plans. One of the main goals of these discussions is to help students reflect and generalize from the specific case they are investigating to the principles of natural selection. We also hope that through these discussions students will develop a better understanding for the methods and strategies that are available and how to apply them, and view science as a process of model building and evidence-based argumentation.
Brian J. Reiser
Investigation Environment Design:
Art and Graphics Design:
Tammy Porter Massey
The computer software described here has been developed for the Biology Guided Inquiry Learning Environments (BGuILE) project, directed by Brian J. Reiser, School of Education and Social Policy, Northwestern University. Although the authors believe these materials can engage students and teachers in a valuable learning experience, neither the authors nor Northwestern University make any warranties regarding the efficacy of these learning materials. These materials are to be used for educational purposes only. BGuILE is funded by a grant from the James S. McDonnell Foundation.
Copyright © 1997-2000, Northwestern University. All rights reserved.
Last updated on April 7, 2003.
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