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Modified by Beth Kramer
Adapted by Larry Flammer




Classification can (and should) be used to illustrate more than a mere hierarchical grouping of organisms. This lesson introduces students to the building of cladograms as evolutionary trees, showing how "shared derived characters" can be used to reveal degrees of relationship.


Modern classification is based on evolution theory.


1. Degree of similarity of basic structure suggests degree of biological relationship.

2. Homology: When corresponding structures in different species are alike in basic structure and origin, implying common ancestry.


 Students will.....

1. Given some groups of organisms and some of their distinguishing characteristics, the student will construct a cladogram.

2. Given a cladogram, the student will properly interpret and analyze that cladogram in terms of recognizing the concepts of common ancestry and degrees of evolutionary relationship.

3. Given a cladogram of vertebrates and some new "unclassified" vertebrates, the student will show where the new animals would be placed.


1. Examples of cladograms from a suitable reference, e.g.Strahler, A.N. "Science & Earth History" . 1987 Prometheus Books. Page 328 (here's a pdf copy of this). Make overhead transparency for class introduction, and/or make copies for students, and attach to background sheet. This book (along with many others) is available at discount from Amazon; it's an excellent teacher resource for topics on evolution, creationism, and the nature of science.

Also, compare with "family trees," e.g., in Figure 17.7 of the BSCS Blue Version: Biological Science, A Molecular Approach. 1996 Heath. Page 388. Figure shows a tree based on morphology (visible structures) and another tree based on molecular comparisons (proteins and DNA).

2. Specimens and/or pictures or diagrams of the organisms presented here. Old texts might be a good resource for this.

3, For Appropriate Responses to WS, send email request to Webmaster. Plesae use your school email address, and specify title of this lesson.

4. Optional: Try the "Making Cladograms" PowerPoint donated by ENSI teacher Dan Patrick.


One 45 - 60 minute period.


   (see end of lesson for the formatted handouts).

1. Background and Procedures (two pages; copy back-to-back on one sheet per student/team)

2. Worksheet (two pages; copy back-to-back on one sheet per student/team)
(See PDF version at end of lesson).

3. If the animals (and their diagnostic features) are not presented in your textbook or classroom resources, have your students search the internet. For this purpose, you can use animal name for each keyword. For the purposes of this lesson the, Wikipedia information should be suffiecient. Likewise, search for each trait (e.g., notochord, amnion, etc.) in Wikipedia.


1. This lesson is best presented after an introduction to the concepts and terminology of hierarchical classification and systematics, and the students have had some activity time to practice using this information.

2. It is also assumed that the students have had a chance to survey the major groups of organisms (kingdoms, and at least the major phyla, and classes of animals), their defining features, and common examples of each. Ideally, this was done in an earlier grade, requiring perhaps only a quick review. Otherwise, an overview of those groups at this time would be very helpful.

3. There is no need to have discussed the concept of evolution prior to this lesson. In fact, the casual discussion of degrees of similarity of structure being associated with degrees of biological relationship (analogous to family traits in people indicating relationships) may be a useful way to introduce the concept of descent with modification. You can label this "evolution" now or later, depending on the comfort level for this topic in this class at this time.




1. Hand out the student packets (Background/Procedure and Worksheet) for students to read quietly.

2. When students have generally finished reading the introductory paragraphs, ask for questions. The questions and your responses should lead logically into the next step.

3. Display diagrams showing the features to be used (on overhead, slides, or large charts). These can serve as review, or they may be new to your class. Explain the diagrams as necessary.

4. Display the blank Data Table (on overhead, or large chart). Select any organism, and consider (with class) each of the seven features in turn, marking an "X" in the appropriate box where that organism has that feature.

5. Let students (individually or in teams) complete their tables, and continue with their Venn diagrams and their cladograms.

6. Walk about, checking progress, giving help as needed.

7. Students are to finish assignment as homework, if necessary, to be handed in or discussed next day (see key sheet at end of lesson).


1. Each student or team completes the assignment correctly (see KEY at end of worksheets, for use by teacher, or students for self-checking).

2. Give a test with another set of organisms and a similar set of characteristics for students to analyze, draw a cladogram, and answer questions reflecting their proper completion, interpretation, and application of the diagram (see Assessable Objectives).



1. If the class seems interested, or needs a little more practice, have another set of animals (or members of another kingdom), definitive shared derived characters for the group, and have them build another cladogram.

2. A logical next step would be to do the ENSI lesson "Molecular Biology and Phylogeny", in which amino acid sequences in cytochrome c are compared for these same organisms. Students discover that the results match the cladogram based on anatomy. This lesson serves as an excellent example of "independent confirmation", based on different evidence; this is one of the reinforcing tools of science.

3. This might also be a good time to introduce "Tree-Thinking" as it pertains to ancestry and biological relationships. For example, a common misconception is that ancestral relationships are often thought to be lineal - straight lines back through time. In reality, such relationships are more like a branching tree. Click Here to see how a cartoon can help understanding.


1. See "The De-riving Force of Cladogenesis" by Andrew J. Petto, on this site. It is a clear and concise explanation of the concepts and terms of cladistics. This could be copied and printed as a student handout. (Click on the "Back" button of your browser to return here.)

2. Get the excellent article "Why Cladistics?" (Gaffney, E.S., L. Dingus, and M.K. Smith, Natural History Magazine, 6/95, pp. 33-35.) from your public or university library, and have students read and discuss it. See the Mini-Lesson on this site for sample Reading Guides for this article.

3. Get the essay by Stephen Jay Gould "What, If Anything, Is A Zebra?", found in the author's book Hen's Teeth and Horses' Toes, 1994. W.W. Norton & Co. (available at discount from Amazon). Have students read and discuss it. See the Zebra Mini-Lesson on this site for a sample Reading Guide / Worksheet and key for this article.

4. The UCMP (University of California Museum of Paleontology) has an excellent presentation of cladistics, phylogenies, and modern systematics (what, why, when, and how). Take a look at it: (<http://www.ucmp.berkeley.edu/exhibit/phylogeny.html>).

5. See the excellent online tutorial by the UCMP: "What did T. rex taste like?" It makes an excellent introduction to classification, phylogenetic trees, and cladistics. This could be given as a homework assignment (online).

6. For an excellent tutorial to introduce phylogenetic (evolutionary) trees, see our review of an article in the American Biology Teacher.

7. See the Cladistics is a Zip-Baggie lesson. It uses a series of nested plastic bags as a 3-dimensional Venn diagram to illustrate the hierarchical grouping of organisms based on their shared derived characters, thus forming the basis of a cladogram.

8. See "Reconstructing Trees: Cladistics" (on Understanding Evolution website).


Some of the ideas in this lesson may have been adapted from earlier, unacknowledged sources without our knowledge. If the reader believes this to be the case, please let us know, and appropriate corrections will be made. Thanks.

1. Original Source: ?

2. Modified by: Beth Kramer; Larry Flammer (6/96)

3. ENSI / SENSI original developed by:

4. Reviewed / Edited by: Martin Nickels, Craig Nelson, Jean Beard: 12/15/97

5. Edited / Revised for website by L. Flammer 3/04/98
Removed key 5/20/11.

6. Some revisions: 1/29/14


MAKING CLADOGRAMS Packet (4 pages):
Background, Procedure (2 pages)
Worksheet (2 pages)

 Strahler: Page 328, Figs.33.4, 33.6
Building a Cladogram


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