I recently took over teaching “Organisms and Populations,” which is the second half of an introductory biology sequence for majors at my university. The first half of the semester emphasizes the relationship between evolution, form, and function with the running theme of “thinking like a scientist.” The second half of the semester focuses on ecology while weaving in the interconnectedness of the concepts covered earlier in the semester. Ultimately, I try to minimize lectures and instead immerse students in conceptual thinking. This article outlines the evolution module I taught during the first four weeks of the semester. I should note that my course, which averages 20 students per section, is taught in a 3-hour block once per week; however, these activities could easily be split up in two or three shorter sessions per week.

Introduction to the Course

To begin the semester, I explained the overarching plan for the course. On the first day, students were presented with the AAAS Vision & Change core competencies and the basics of scientific disciplinary practice for undergraduate biology education. In addition, students were made aware of the following:

• This course is based on understanding and application to help them practice being a biologist.
• The biological concepts in the class are interrelated: they will be introduced and revisited over the course of the semester in different contexts.

I think it’s essential to provide students with insight as to how the class is designed and what the expectations for assignments will be in order to prepare them for the high demands of the coursework.

Week 1: Experimental Design & Nature of Science

The first week’s class consisted of a basic review of the parts of the cell, taxonomy, and phylogenetic trees, with a major emphasis on the nature of science and experimental design. We started with a species profile activity that has a dual purpose. It acts as a review of taxonomic relationships at a basic level, as well as an icebreaker. I provided students with a table in which they compared two species to see the taxonomic level at which they are most closely related.

The second half of the class period focused on the process of science. Students were provided with the How Science Works diagram as a reference throughout the semester because we revisit the process of science as a running theme in various assignments. I made a printed handout for students using a screenshot of the diagram. I held a mini-lecture on experimental design with a think-pair-share discussion to identify misconceptions about the process of science. This was followed by the video case study for The Effects of Fungicides on Bumble Bee Colonies. It is an excellent resource for introducing experimental design, since it has embedded case study questions with strategic stopping points. Because I did these activities on the first day of class, I had the students answer these questions in larger groups to encourage discussion. This activity engaged students, helping to set the tone on the first day.

Week 2: Origin of Species & Evolutionary Theory Introduction

I began the second week’s class with a 15-minute mini-lecture covering evolutionary theory, which mainly emphasized the timeline of the theory’s development and the major scientific players involved. I followed this with an activity for the short film The Origin of a Species: The Making of a Theory to introduce the concept of a scientific theory, as well as introduce students to Darwin and Wallace. Students completed the worksheet while watching the video and were then given 10 minutes to consult with their elbow partner to discuss and verify their responses. As a group, we discussed the questions to ensure accuracy. I want students to understand that science begins with observation and inquiry, and that good scientific theories begin with a solid foundation of evidence. Scientists then use hypotheses via the scientific method to develop experiments to help support (note the word choice — emphasize “support” vs. “prove”) the theory.

After completing the video activity, we spent the second half of the class exploring the relationship between ecological niches, adaptive radiation, and what defines species. I provided students with a mini-lecture on these topics, which included the animation Reproductive Isolation and Speciation in Lizards, to help further emphasize the point of speciation. We then watched the short film The Origin of Species: The Beak of the Finch. Students were asked to take notes during the video, which they used for a later activity. My aim was to have students start identifying the similarities in the speciation patterns between the finch and the lizard examples. At this point in the lesson sequence, I had not explicitly identified the relationship between ecological niches and speciation, nor had I pointed out that adaptive radiation occurred in both species. 

Each topic was presented in a separate mini-lecture (2-3 slides) so that students could make their own connections by watching The Origin of Species: Lizards in an Evolutionary Tree. Students made lists of similarities and differences in comparison to the Beak of the Finch story and then compared lists with their elbow partner. As students worked with partners, I asked guiding questions to ensure they could make the connections between ecological niches and speciation. The comparison lists and responses to my questions were added to their notebook for use during Week 3 and used as references when completing their culminating case study assessment in Week 4.

Week 3: The Relationship of Evolution to Form and Function

The purpose of this week’s class was to make the connection between speciation and form/function. As preparation for this week’s unit, students were assigned the Great Transitions Click & Learn in advance to provide them with a basic understanding of tetrapod evolution. To maintain student accountability for completion of the assignment, I created an interactive “lecture” that incorporated a quiz over the material using student response cards.

Response cards are a team assessment approach that uses scratch-off cards to record answers. The response cards are similar to a lottery scratch-off card. Each card is numbered with four answer choices: A, B, C, and D. Each letter must be scratched off to see if it is correct. Students work in teams to determine what they think is the correct answer. Once they decide, they scratch off the corresponding letter. If it is correct, a star will be present once they scratch off the answer. If not, they must try again until they get the correct answer. Scoring for this quiz is based on how many tries it takes to get to the correct answer. The scoring system I use for this gives students three points for a correct answer on the first try and a decreasing number of points for each additional attempt. The questions for this quiz were used to assess understanding of concepts covered up to this point and to apply these concepts to the new material on tetrapods.

We then watched a short clip of the Your Inner Fish video about Tiktaalik, the famous transitional tetrapod, and answered two questions using the team response cards. If you would like to expand the module, more resources for Your Inner Fish can be found here. I asked the following questions (answers bolded):

Question 1: Which statement below is evidence that all tetrapods shared a single common ancestor?

1. All tetrapods live partly in water and partly on land.
2. All tetrapods are warm-blooded.
3. All tetrapod limbs have a common pattern of one bone, two bones, and many bones, then digits.
4. All tetrapod limbs consist of rearranged fish fin rays.

Question 2: The transition from fish to tetrapods is best described as:

1. Like most of the great transitions in evolutionary history, it happened in many small steps leading to many intermediate forms.
2. Like most of the great transitions in evolutionary history, it happened in very few big steps so that there are few intermediate forms.
3. Like no other transition in evolutionary history, it happened in many steps, so there are many intermediate forms.
4. Like most of the great transitions in evolutionary history, it happened in a single step with no intermediate forms.

Next, students completed the Comparative Anatomy of the Domestic Chicken Click & Learn in teams of two on laptops. This is a great activity for students to make connections with evolutionary theory, niches, and the tetrapod assignments. By the end of the Click & Learn, students have created their own phylogenetic tree!

After that, we watched the short film Great Transitions: The Origin of Birds. Students were asked to take notes during the video. These notes became the only reference materials students could consult for the remaining review questions, which I adapted from the accompanying film activity. These questions included the following (answers bolded):

Question 1: Which of the following describes how Dr. Jack Horner’s discovery of dinosaur nesting grounds supported the hypothesis that birds evolved from dinosaurs?

1. It provided evidence that, like birds, some dinosaurs laid eggs.
2. It provided evidence that, like birds, some dinosaurs migrated to reproduce.
3. It provided evidence that, like birds, some dinosaurs cared for their young.
4. It provided evidence that, like birds, some dinosaurs huddled together for warmth.

Question 2: Which of these combinations of characteristics is typical of modern bird species?

1. teeth; claws; fused fingers; long, bony tail; and flat sternum.
2. no teeth; no claws; fused fingers; short, bony tail; and deep-keeled sternum.
3. teeth; claws; fused fingers; short, bony tail; and deep-keeled sternum.
4. teeth; no claws; fused fingers; long bony tail; and flat sternum.

Finally, this class period culminated in a PowerPoint case study from the National Center for Case Study Teaching in Science (NCCSTS) titled “A Whale of a Tale? The Evidence for the Evolution of Whales.” This case has embedded reflection and discussion questions, which help students apply the principles of natural selection to yet another group of species. This final activity served as an excellent review for the quiz over this module, which was embedded into Week 4.

Week 4: Assessment

During the Week 4 class, students took a short quiz, which focused on the major concepts covered in the previous weeks and required them to analyze figures similar to those used as examples in class. Instead of using the “Student Handout” for The Origin of Species: Lizards in an Evolutionary Tree as an assignment or class worksheet, I took screenshots of the graphs and used the questions to create a quiz. I did this because I also created some of my own questions; however, you can just use the worksheet as a quiz in its posted form. Here is an example question:

In 2003, Jonathan Losos and his research team experimentally introduced curly-tailed lizards (Leiocephalus carinatus) to islands populated by trunk-ground anoles that live primarily on the ground and have relatively long legs (Losos, J. B., T. W. Schoener, and D. A. Spiller. 2004. Predator-induced behaviour shifts and natural selection in field-experimental lizard populations. Nature 432: 505-508).

The scientists wanted to know how the presence of the curly-tailed lizards, which are anole predators, would affect the habitat in which the anoles lived. In one experiment, Losos and colleagues measured the “perch height” (or how high off the ground a lizard was perched) for 24 individual anoles. They then placed either a curly-tailed lizard (experimental population) or an inanimate object of the same size (control population) in front of individual trunk-ground anoles and measured the perch height 10 minutes later. They then calculated the average change in the anole’s perch height in the experimental and control populations. The results of this experiment are summarized in Figure 1.

After this in-class assessment, we discussed knowledge vs. memorization as a key factor to meaningful learning. This provided a transition to the take-home assessment for this unit, which consisted of a second case study from NCCSTS: “It’s a Crocodile! No, a Fish! No, a Dolphin!” I used only the first three parts of the case study as the assessment. Part 1 of this case study asks students to review the skeleton of a newly found fossil and then develop a hypothesis using their existing knowledge of natural selection and the evolution of tetrapods. I required students to provide evidence for their hypothesis. Thus, they applied two concepts covered during the first unit: scientific thinking and the theory of evolution. Parts 2 and 3 of the case study delve more into review of the scientific method by asking students to 1) compare the scientific process of fossil collecting to forensic science and 2) identify how the scientific method is applied in both situations. In the end, students reconsider their original hypothesis and must further justify their reasoning. I required them to provide citations to justify their responses.

Overall, I feel that the students from both sections of my course enjoyed the activities, and their quiz scores showed that they had an understanding of the material covered in the module. When I taught this class at another institution early in my teaching career, I had an instructor-centered classroom in which I mainly lectured and gave exams. No pun intended, but my teaching has now evolved over the past 15 years as well. Based on students’ comments, engagement during the activities, and resulting quiz scores, I am happy with this new sequence and new way of teaching this material. When grading the quizzes, I noticed that students were able to actually apply the concepts to an example using another species. This tells me that they were not just memorizing or guessing on multiple-choice questions. In addition, they could use terms appropriately to answer the questions. I’m looking forward to teaching this again next year and tweaking a bit.

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