| 1 | <p>Over the past four decades, evolutionary biologists Rosemary and Peter Grant have documented 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 million to 3 million years ago. </p> | 1 | <p>Students first watch the 15 minute video “The Origin of Species: The Beak of the Finch” to give them sufficient background on the Grants’ research on Galápagos finches during the drought of 1977. This sets up the context of the selective pressure these finches were exposed to, and the types of measurements and data that the Grants collected.</p>
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| | | 3 | <p>Students then work through a three-part worksheet and accompanying dataset. The first part of the worksheet works through the graphs using beak depth: It first shows the frequency distribution of beak depth in populations of finches before and after the drought, has students calculate the selection differential for beak depth in this circumstance, and make predictions about the offspring of the finches that survive the drought. The second part of the worksheet introduces students to the four modes of selection, and shows the fitness function of beak depth in the population of finches that survived the drought.</p>
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| | | 5 | <p>Finally, students are given access to a dataset of 100 finches with measurements of weight, wing length, tarsus length, beak length, and beak width, and are asked to select a trait of their choosing and make a hypothesis and prediction about how this trait might be influenced by the selective pressure of drought. To test their hypothesis, they then calculate means, calculate a selection differential, graph a frequency distribution, graph a fitness function, and answer some follow-up questions. Step-by-step protocols are provided for how to use a spreadsheet program to calculate a selection differential, graph multiple frequency distributions on one set of axes, and graph a fitness function.</p>
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| | | 7 | <p>Materials include:</p>
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| | | 9 | <p>• Video (“The Origin of Species: The Beak of the Finch”)</p>
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| | | 11 | <p>• Worksheet (Parts 1, 2, and 3)</p>
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| | | 13 | <p>• Finches Dataset (from “Evolution in Action: Data Analysis”)</p> |
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