# The Problem of Scale in Evolution

Created by Jillian Banks, Jeremy Brown, Cindy Gordon, Chris Gregg, Travis Marsico, Chris Osovitz, and Rebecca Symula, this activity focuses on the importance of temporal scale and specifically seeks to resolve the common student misconception that evolutionary change is only observable on a single timescale.  It utilizes index cards in an interactive jigsaw.According to the authors, "During the activity, students are paired. Each student pair is given a set of index cards with pairs of organismal pictures. Groups have instructions to rank these pictures by either (A) the amount of morphological change that has occurred since these species diverged from their last common ancestor or (B) the amount of time elapsed since species divergence. After ranking, A groups are paired with B groups and the two ranking types are compared. Students then flip cards over to reveal colors, where they are told that only a single sequence of colors is correct. In resolving discrepancies, students should come to the conclusion that perceived morphological disparity between species may be decoupled from the amount of time since they diverged."

(Text from the Yale Center for Scientific Teaching's Teachable Tidbits).

Here is a sample activity sequence:

Learning Outcome: Students will resolve the misconception that evolution happens at a single time scale.

 Time Required Activity/assessment Explanation, notes, suggestions, tips 2 hrs. - 3” x 5” Index cards – white (5 per group), color (5 cards per group, each card a different color) - Printed paired images reflecting various combinations of divergence time and degree of morphological difference (e.g. wolf and domestic dog, human and sea turtle, etc), small enough to fit 1 pair of images per card - glue stick and scissors - Printed instructions for Group A (morphology) and Group B (time) For each group of cards: - Glue a white card to each color card, so that one side is white and one side is colored (=activity card). - Choose a single color to be the instruction card in each group, and glue the printed instructions to the white side of the card (=instruction card). - Choose a sequence of colors for the activity cards (e.g. pink = 1, green = 2…the sequence is arbitrary on which color is first or second, etc). - Now, generate the sequence of images for both groups: First, rank Group A images from most similar morphology to least similar (e.g. 1 = most similar morphology, 4 = least similar morphology). Next, for the Group B images, assess the relative amount of time that has passed since the divergence of the two species on each image. Rank Group B images from most recent divergence to oldest divergence (e.g. 1 = most recent divergence, 4 = most ancient divergence). - Now glue the images ranked #1 in both groups (I.e. most morphologically similar images for group A and most recent divergence for group B) to the white side of the color card you’ve ranked #1 (e.g. pink in our example). Continue to glue the ranked images to the white side of the remainder of the ranked colors (e.g. image #2 pasted to color #2, image #3 pasted to color #3, etc.). - At this point, you should have an instruction card and a set of four activity cards for both group A and group B, where there is a pair of images on the white side of each card. The color of each card should only be visible once turned over. - It is recommended to write the letter “A” on the color side of all the A group cards, and write “B” on the color side of all the B activity cards to keep the cards organized. 5 min. - The introduction for this activity is intended to be very brief. Simply introduce that this activity will deal with the idea of evolutionary time, and pose pre-assessment clicker question. Then describe the instructions for the activity, and then pass out the cards (described below). It might be advisable to pre-arrange your students in rows/groups, depending on classroom layout. 15 min. - Verbal instructions for students: Before you pass out the materials, explain that the students will need to pair up and follow their specific instructions on their instruction card. - Pass out the cards and monitor progress. (5 minutes) - Once they’ve mostly finished their rankings, get the class’ attention again. Explain now that every A group needs to pair up with a B group. (You may want to notify the students that the two groups have differing instructions.) Have them compare and contrast their rankings and discuss any discrepancies. (2 minutes) - Gain the students attention again, and have them flip over their cards, preserving both groups’ rankings. Explain that there is only one correct color ranking that applies to both groups. Have them discuss. (3 minutes) 10 min. - Elicit discussion outcomes from groups. Engage the class in this discussion. - Show correct answers in powerpoint slides, beginning with most recent divergent pair (in our example, it is a dog/wolf pair). Discuss similarities and differences between the images on each slide with students. Continue though to the slide with most ancient divergence (in our example, it is the moss comparison). - Show and discuss the final composite answer slide (I.e. the slide with both morphology and divergence image ranks and the color rankings). - Pose post-assessment clicker question and discuss how student perceptions may have changed. Explicitly emphasize central learning outcome.