Classification Unit

 Phylogenies & Tree-Thinking

 PDF Copy of this page for printout

Your Family Tree versus
a Phylogeny (Evolutionary Tree)
and a Common Misconception

We often think of our ancestors as those that they lie in a linear path over many generations straight to us (our parents, grandparents, great grandparents, etc.). In reality, your ancestors include those lineal generations and their respective offspring branching off along the way (your siblings, cousins, second cousins, etc. - your lateral ancestors. This takes on the form of a branching tree.

In a similar way, evolution is often displayed as a linear path through earlier ancestors in different groups. In fact, as for family trees, evolution produces a branching tree pattern, with different groups branching off from shared common ancestors along the way.

The following stick-figure cartoon was created by Matthew Bonnan of Macomb, Illinois for a stick-figure cartoon contest in the Summer of 2010 by the Florida Citizens for Science. The cartoons were to illustrate common misconceptions in science. Matthew's cartoon was judged #6. With the kind permission of the Florida Citizens for Science, we are sharing that cartoon below. It nicely illustrates the misconceptions described above. Click here for a version in vertical format that you can download and print directly to use for overhead or PowerPoint slide.

 

 WAYS TO PRESENT THIS:
1. Display the entire cartoon - all four panels at once. Ask students to study it and then ask for individuals to "explain" it - to point out why what is NOT right is not right in each case. Get a few or several different versions of this - perhaps exploring questions that may arise in the process. Finally, wrap it up with the essential points described above, especially as they were reflected in the explanations.

2. Remove (or mask) the titles from all 4 parts, and separate the 4 parts (or prepare to mask 3 at a time while showing one of them). First, show the lineal family tree - without its title. Ask "What does this illustrate?" Get several different ideas on that. Then show the branching tree - without its title. Ask "What is this?" After several responses, show them both together (without titles), and ask "How do these compare? Are they just two ways for showing the same thing?" "Is one better than the other? Which one?" "Is one right, the other wrong? Why?" Repeat these steps and questions with the other two frames. Hopefully, students can be guided to see, when showing both pairs together, the similarity of the two "NOT" frames, and the similarity of the two "IS" frames.

3. Say "Draw a diagram of what you think your family tree would look like, showing at least you, your parents and your grandparents." After each student has done this, ask some of them to show their results to the class, pointing out its features. Hopefully, some diagrams will be like the NOT version, some will be closer to the IS version. Carry out a discussion with wrap-up similar to the previous approach.
Then, say "Draw a diagram of what you think the evolution of a whale (or elephant, or giraffe, or whatever) would look like. Hopefully, some diagrams will be like the NOT version, some will be closer to the IS version. Carry out a discussion with wrap-up similar to the previous approach.

4. You might also want to provide copies of an article by T. Ryan Gregory on reading evolutionary trees: "Do You Understand Evolutionary Trees?" They can be downloaded in two parts: Part One and Part Two. If you reduce sizes of the diagrams (click in lower right corner of each and drag diagonally toward center, about 2 cm), and increase font size to 12, you can condense both articles together into about 8 pages.

APPLICATIONS:
FAMILY PLOT IN GRAVEYARD - TO DIGGING FOR REMAINS: It might be helpful to describe the family plot of a longstanding graveyard, with many generations of your family buried there, but with the markers and headstones long since lost or removed. If we were to dig at random to search for the remains of your ancestors, which would we be most likely to find: direct, lineal ancestors, or long lost cousins? [Since there are likely to be many more cousins than direct lineal ancestors, each discovery would most likely be a cousin.

DIGGING FOR FOSSILS: In similar manner, apply the likely results to digging for fossils of a particular group of animals. Would each find most likely be a lineal ancestor, or a lateral ("cousin") ancestor? Right - most likely a lateral ancestor. This is a most important point, and provides the rational for why humans did not evolve from monkeys or even apes, but rather the evidence clearly points to a shared common ancestor that was neither human nor monkey. Furthermore, all the fossils we find or early humans are most likely not lineal ancestors, but rather members of branch groups along the way. However, we do infer that those "cousin" branch group fossils were probably similar to that common ancestor, so each fossil find is a clue to our likely ancestry.

These applications explain the likely status of fossils relative to living groups of organisms. I derived them from a presentation by Eugenie Scott, Director of the National Center for Science Education (NCSE).

 CLICK HERE download a PDF file of the stick-figure cartoon in vertical format.