A Tree of Life Activity
Authors: Nicole VanderSal
Overview: This lesson first introduces a large diagram of the Tree of Life that will be a reference for the evolutionary relationships of California organisms for the rest of the year. Then there is a class-participation activity using traits of organisms on the tree to determine the identity of a mystery organism.
Grade Span: 912 (can be simplified for younger classes)
Time: 50 minutes
Begin by putting up the Tree of Life poster and pass out small copies of the Tree of Life for students to follow along with. Go over organism groups on the tree that the students do not know. Explain that all living things have a place on the tree of life. Organisms are grouped by their similarities and differences. In addition, the branches show how groups of organisms are evolutionarily related to each other.
Explain the concept of "Character" as a trait of an organism that we use to identify the organism and group it with other organisms that are similar. You should emphasize that certain characters of an organism are not useful for grouping things together on a large scale (i.e., bird, bat and insect wings, or red flowers, insects and birds) but can be useful to separate organisms into small groups (species). Starting at the bottom of the tree, work as a class to determine what characters all organisms beyond a branch have in common (see list at bottom of lesson). Remind the students that these are just some of the characters that scientists use to group organisms based upon their evolutionary relationships. Other characters that we cannot directly see are also used to construct the tree of life: DNA sequences, development of embryos, and bone structure.
Give an introduction to the mystery organism activity:
First have the class make a list of organisms or parts of organisms that might be found in the air at some point (naturally). Pass out pictures (or specimens) of the organisms as they are listed and have the students tape the picture where those organisms should be on the tree of life and what characters the organisms have (based upon characters you established from the beginning of the lesson). This activity reaffirms the idea that organisms, though they may look similar or act similarly, are more closely related to other organisms with more similar characters.
Once students have come up with all of the organisms, say that you will start at the bottom of the tree for the mystery organism. You should have the following list covered so that you can show one character at a time:
With each answer, have the students determine which branch on the tree of life you should follow (this helps the students understand that all organisms beyond a branch will share that characteristic). In the end, have the students guess the identity of the mystery organism. Show the picture or specimen. If there is time, you can bring up the concept of body specializations that the flying squirrel has for its nocturnal, gliding lifestyle: skin flaps, long, flattened tail, large eyes and ears.
Throughout the year, you can return to the tree of life to tape photos of animals and plants collected from the school yard and field trips. If the class learns about a group in more detail (i.e., insect orders), the branches of the tree be expanded out to show this new information. In this way, the tree can tie the year's activities together.
Characters on the Tree of Life
This lesson really emphasized characters used for making the Tree of Life, but as with any whole class activity/discussion, some students were more involved than others. From this activity it was difficult to assess whether every student understood the concepts of characters and how/why the animals are related. We used pictures of the animals, and I think the activity would be better if the students could see specimens to really see the characters that are on the Tree of Life. I think that slight modifications of the lesson could make it very salient for the students: perhaps by breaking them up in groups for more discussion, but I am not sure how to incorporate that in the current lesson.