Speciation

The two theories of speciation (gradualism and punctuated equilibrium) are frequently confused, both with each other and with the concept of evolution in general.

Group: Your Number Group

Goals:

    • Apply the concepts of gradualism and punctuated equilibrium

    • Apply scientific processes to describing, interpreting, and evaluating data on speciation

    • Help explain the differences between the two main theories of speciation

Procedure

    1. Reintroduce yourselves, and make sure everyone knows each other's name.

    2. Within your group, divide into roles as follows.

        1. Member of group with darkest-colored shirt: recorder The recorder will take notes on the group's discussion. If anything needs to be turned in, the recorder will take care of it.

        2. Next darkest shirt: time-keeper The time-keeper makes sure the group stays focused on the activity and completes the steps on time.

        3. Second-lightest shirt: presenter The presenter will speak for the group during the whole class discussion.

        4. Member of group with lightest-colored shirt: leader The leader makes sure every voice is heard, and helps encourage the group to stay on-task

    3. The recorder should write down each person's full name, making sure it is spelled correctly, on the top of a piece of notebook paper.

    4. You will be shown a picture of geological layers with fossil shellfish, showing the evolution of a specific shellfish species. Each layer represents a different time period, with the layers on the bottom representing older time periods and the layers on top more recent time periods. These layers were laid down over several million years.

    5. As a group, take five minutes to describe the variation (differences) that you see in the shellfish. You should describe only, meaning "just the facts", without your interpretations or explanations. What can actually be seen or measured about these shellfish and the geographic layers? The recorder should write down the variation your group describes.

    6. Spend two minutes interpreting the changes that you see in the shellfish through time. Do you believe all the shellfish are the same species throughout the time represented by the layers? If not, when do the shellfish change from one species to the next, and what criteria are you using to decide to split the species?

    7. In five minutes create two hypotheses to account for the change through time that you described. One hypothesis should use the concept of gradualism, and the other should use the concept of punctuated equilibrium. The recorder should write down your hypotheses.

    8. As a group, take ten minutes to discuss what data you would need to test your hypotheses. Think widely and creatively. Do you need to learn more about fossils of other animals at the time? Do you need to learn more about the environment during each time period? Make sure you know how the data would help support or refute your hypothesis.

    9. The presenters will share your hypotheses with the whole class.

    10. As a class, we will discuss what data is needed to test the hypotheses, and why.

Take-home Messages

    • Gradualism and punctuated equilibrium are separate theories to explain the process of speciation

    • More than one hypothesis can be proposed to explain the same data.

    • The process of science involves describing data, creatively considering hypotheses, and testing them by gathering more data.

Reflection

Take five minutes to reflect on the activity. You may reflect on any aspect of the activity, but if you have trouble, consider answering these questions: What is the most important thing you learned from this activity?