Darwinian Snails and Evolution

by Colleen Worrell, Secondary Technology Integration Coordinator

AP Bio students kicked off Semester Two by using SimBio to get crabby. Teacher Michelle Odierna used the hands-on Darwinian Snails virtual lab to help her students understand the range of variables that influence the process of natural selection. SimBio is a digital tool, paid for by an HEF grant awarded to Science teacher Charlotte Shire in 2011. The app enables students “to conduct simulated experiments similar to those performed by practicing scientists, in fields of biology where live experiments are impractical or impossible” (SimBio site).

Students were put in teams to “become a European green crab.” As the lab explains, “You will feel especially crabby if you are not getting enough to eat, and the best snacks available on the coastline are these tasty looking snails. All you have to do is crack their shells by pounding on them with your claw.” The student teams manipulate variables in the population in order to determine how these variables affect the population’s evolution. They make predictions, create models, test hypotheses, and analyze data to explore and further their understanding of population genetics. Students collaborate each step of the way, going through exercises where the crab eats snails using the Claw tool and they try to keep the “Crab Happiness Score” high by eating their snails with the fewest clicks possible. Meanwhile, as the snail population reproduces, the student-biologists track variation in shell thickness as some snails die out and new snails are born. The final exercise asks students to consider bigger questions about “What Makes Populations Evolve," e.g., “What role did the predators play in causing the population of snails to evolve?”

A visitor walking into the classroom would find the AP Bio students hard at work, barely pausing as Mrs. Odierna visits each team to check in on their progress. “Awwww!” one group yells, when they let their crab overeat and too many snails are gobbled up. They laugh as they review the impact, noting that green snails, with softer shells, were eaten, whereas red and yellow snails, with harder shells, tended to survive. “Let me know if the red population goes down as I do this,” one of the trio exclaimed, as they continued on with the snail simulation.

During the wrap up discussion, students shared additional things they learned about natural selection and the factors that make it possible. For instance, one student added “selective pressure” as another criterion that makes natural selection possible. During their discussion Ms. Odierna and her students linked selective pressure back to their study of sickle cell anemia during last term. The students agreed that they liked doing this not only because the experience was more like a fun, video game than a traditional "lab," but also it helped them to experience and better understand how natural selection works.