Troublesome concepts such as randomness, probability and temporal scale have been suggested as important for understanding evolution. I e earlier research has shown that learners often fail to grasp the random component of natural selection and tend to conceptualize adaptation as directed or driven by the needs of the organism. There is some evidence in the literature that interventions targeting randomness in evolution might contribute to better understanding of natural selection. Since external representations such as visualizations has the potential help learners grasp difficult concepts in science, we designed an interactive visualization that focus on some of the troublesome concepts of evolution. The aim of the present pilot study was to explore possible effects of the application on students reasoning as part of a guided group exercise. In particular, we were interested in whether the aspects focused on in the application were discussed and if the students were able to transfer the symbolism in the application to the process of natural selection. The empirical data (recorded interviews and written answers) were collected during a biology course for primary teachers (n=14) and subjected to qualitative content analysis. We found that students’ engagement with the task and in the discussions was high. The transcripts revelead frequent analogies between the visualization and examples from evolution. Accumulated and gradual change over time also was a recurrent theme. Thus, our preliminary results add support to reports suggesting that using interactive visualizations in combination with pre-worked tasks and peer-discussion can facilitate students’ cognitive development of troublesome concepts.