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Natural Selection and Galápagos Finches

By Liesl McCormick

Pacific University

A worksheet and accompanying data set that guides students through making and interpreting frequency distributions, selection differentials, and fitness functions.

Listed in Teaching Materials | resource by group HHMI BioInteractive FMN (2017)

Version 1.0.0 - published on 21 Feb 2018 doi:10.25334/Q4339Q - cite this

Licensed under CC Attribution-NonCommercial-NoDerivatives 4.0 International according to these terms

Adapted from: Finch Evolution Collection v 1.0



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.

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.

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.

Materials include:

• Video (“The Origin of Species: The Beak of the Finch”)

• Worksheet (Parts 1, 2, and 3)

• Finches Dataset (from “Evolution in Action: Data Analysis”)


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To modify this resource, I combined parts of and added to three existing resources:

• The Origin of Species: The Beak of the Finch. Students watch this video in its unmodified entirety.

• Effects of Natural Selection on Finch Beak Size (Data Point). I incorporated the entirety of this Data Point, a single figure analysis, into Parts 1 and 2 of the worksheet. I wrote new, related material to introduce the concept of a selection differential alongside analysis of the frequency distribution.

• Evolution in Action: Data Analysis. I used the dataset from this Data Analysis as the inspiration for Part 3 of the worksheet. I used the dataset to write new material to introduce the concept of a fitness function, and wrote step-by-step instructions for how to graph the data in the dataset as frequency distributions and fitness functions. I also wrote new data analysis questions to tie back in to the concepts explored in the video and data point.

The result of this was one new resource that is a hybrid of the Data Point, Data Analysis, and includes some new material.

HHMI BioInteractive FMN (2017)

HHMI BioInteractive FMN (2017) group image

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