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En Garde! Animal Structures and What They Mean


Parks Collins
Natural Science
Mitchell Community College


In most animals, the drive to breed and produce offspring is strong. However, most males live their whole lives without having the chance to breed. The events leading up to mating can be very dangerous and also very costly to an individual. Some males have evolved elaborate structures, or weapons, as a result. The structures do help males in both combative situations and with attracting females, but ironically, the structures themselves come with certain costs. This flipped case study provides students with the opportunity to not only see how animal structures and functions are linked, but also to see how certain animal structures are needed and costly. There are videos that students are expected to view before the case. The case was initially designed for a second semester college general biology class for majors. However, it can also be used in non-major biology classes. Students should have some background knowledge of natural selection, specifically sexual selection as well as energetic demands of certain structures.


  • Understand how animal structure and function are correlated and natural selection's role.
  • Understand how physical laws and the environment limit, or constrain, animal structures.
  • Define bioenergetics.
  • Analyze data sets.
  • Explain how elaborate animal structures can be costly.
  • Understand why some animal weapons are the result of sexual selection and some may not be.


Animal structure; function; evolution; bioenergetics; weapons; fiddler crabs; Uca pugilator; moose; elk; bighorn ram; narwhal; sexual selection; fitness;

Topical Areas


Educational Level

High school, Undergraduate lower division, Undergraduate upper division



Type / Methods

Directed, Discussion, Flipped, Interrupted



Subject Headings

Biology (General)  |   Ecology  |   Evolutionary Biology  |   Zoology  |   Anatomy  |   Science (General)  |  

Date Posted


Teaching Notes

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Answer Key

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

  • World’s Weirdest- Narwhals
    A narwhal's tusk is actually a tooth that can reach 10 feet in length, and scientists have numerous theories about its powers and purpose. Running time: 2:14 min. Produced by National Geographic Wild, 2012.
  • How Saber-Toothed Cats Grew Their Mouth Swords
    This video discusses some ideas as to how and why saber-toothed cats had large teeth as weapons. Running time: 5:29 min. Produced by Vox. Uploaded to YouTube on July 1, 2015.
  • Battle of the Fiddler Crabs
    This video shows actual footage of two fiddler crabs (Uca stylifer) fighting on a beach. Running time: 2:27 min. Produced by Michael Rosenberg. Uploaded to YouTube on May 10, 2013.
  • Animal Structures and What They Mean
    This video outlines the relationship between structure and function, which is usually complementary; but since some structures are extreme and require an enormous energy investment, structure may sometimes hinder function. Running time: 8:22 min. Created by D. Parks Collins for the National Center for Case Study Teaching in Science. Date: 2015.