Tree of Life #2: Tree Thinking

Authors: Liz Perotti and Guin Wogan

Overview: Building on (and reinforcing) the concepts learned in Tree of Life #1, this lesson asks students to identify characteristics that are shared between different groups of organisms on an evolutionary tree. Through this activity, they learn that these diverse and different groups have similarities because they inherited them from a common ancestor. This lesson uses organisms students observed on a field trip, but the lesson could be adapted to include any organisms. Students will work in pairs.

Lesson Concepts:

  • Students understand that an evolutionary tree is a way of representing relatedness between many species and is one way to represent biodiversity.
  • Students identify and learn features that are shared similarities between different groups of organisms.
  • Students learn that there are many traits that make a species unique, but also many traits they share with other organisms.
  • Students learn that some traits are similar to other species because they are inherited from a common ancestor.
  • Different traits evolve at different times.
  • Students learn that fossils are evidence of past life.


  • Envelope with cards with shared, derived traits (18 per class)
  • Envelope with cards of fossils (18 per class)
  • Handout with evolutionary tree (1 per student; 36 per class)
  • Poster with evolutionary tree and attached pictures (18 per class)
  • Eurypterid casts (2)
  • Insect fossils: larval and adult dragonfly (1 each)
  • Trilobite models (2) and fossils (2)
  • Crustacean fossil (1)
  • Calamites leaf fossils (2), stem fossils (2), coal peels (2)

Time: About 40-50 minutes

Grouping: Students work in pairs

Vocabulary: ancestor, common ancestor, descendent, relatedness, evolutionary tree, node, fossil


I. Introduction (15 minutes)

  1. Students brainstorm organisms observed on the field trip to Alvarado Park or in the school yard. Write list on board and fill in any missing taxa. Taxa should include (plants, fish, amphibians, reptiles, birds, mammals, spiders, and insects).
  2. Draw the Tree of Life (TOL) with these taxa on the board. To reinforce previous lesson, reintroduce terms "ancestor," "descendent," and "relatedness." Ask students to identify the common ancestor for whole tree, etc.
    Assessment: "What would you say if someone asked you if humans came from Neanderthals?" Draw smaller tree on board and reinforce the idea of common ancestry and "sister" groups.
  3. Ask students to identify a few traits that make one of the groups unique. Ask students to identify traits that are similar between sister groups. Demonstrate using plants (i.e., gymnosperms, angiosperms) on the tree. Introduce fossil evidence with the horsetail history (see attached). Emphasize that their common ancestor evolved these traits and each descendent species inherited these traits.

II. Group Activity (20-25 minutes)

  1. Break students into pairs.
  2. Give each group the same tree of life and one envelope with cards of similarities each. Ask students to match them up to the appropriate common ancestors. This should be demonstrated before during introduction to minimize confusion.
  3. Once the group has decided where all the traits go, they should copy them down onto their own TOL.
  4. If a group finishes early, give them a second envelope with three fossils (Ichthyostega, eurypterid, Archaeopteryx) and ask them where they would put them on the tree and to write one sentence about why they made their choice. This was demonstrated before in the introduction with the Calamites sp., ancient relative to horsetails.
  5. Clean-up. All cards should be placed into correct envelopes and collected. Pick up hand-outs.

III. Wrap-up (5-10 minutes)

  1. Assessment exercise with fossils and discussion of their stories.
  2. OR Brief recap of main points. Take a poll with students to see where they put a few of the similarities. Ask students to defend their choices.