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Selection on a Case by Case Basis

Co Authors:

Adam R. Irvine
Biological Sciences
University of Denver

Eva S. Horna-Lowell
Biological Sciences
University of Denver

Mathew J. Driscoll
Geography and Natural Sciences
University of Denver

Emily D. Broder
Biological Sciences
University of Denver


This "clicker case" gives students an opportunity to apply their understanding of three different types of selection (directional, stabilizing, and disruptive) to a variety of model systems. The case describes each type of selection in detail, presents a paradigm case of each, and then uses clicker questions to test whether students can identify the mode of selection in other systems (answers included in the teaching notes).  Nine different studies are presented so that students gain a broad understanding of selection and how environmental factors can impact species differently. The case concludes with an optional discussion activity (also discussed in the teaching notes) to deepen understanding. Although designed for a high school classroom, it could easily be used in a lower-level college course as an engaging introduction or review of concepts. The case could be used at the beginning of an evolution unit, but it would be helpful if the students were familiar with natural selection before completing the activity.

  • Understand the three ways selection can act on traits: directional, stabilizing, and disruptive.
  • Understand how both trait distributions and fitness curves shift in response to those selective forces.
  • Be familiar with examples of each type of selection and be able to identify the applicable type of selection.
  • Improve basic graphing skills including understanding the x- and y-axis, histograms, and distribution curves.
Keywords: Natural selection; evolution; selection curves; selection; types of selection; directional; stabilizing; disruptive;
Topical Area: N/A
Educational Level: High school, Undergraduate lower division
Formats: PDF, PowerPoint
Type/Method: Clicker, Discussion, Journal Article, Mini-Case
Language: English
Subject Headings: Biology (General)   Ecology   Environmental Science   Evolutionary Biology   Science (General)  
Date Posted: 9/24/2018
Date Modified: N/A
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.

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