Final answer:
The shift in the attitudes of a group towards being more strongly against stem cell research best illustrates group polarization.
Step-by-step explanation:
The shift in the attitudes of a group towards being more strongly against stem cell research best illustrates group polarization. Group polarization is the phenomenon where a group's initial attitudes or opinions are strengthened after discussing the topic within the group. In this case, Ashley and her friends started off somewhat against stem cell research, but after their group discussion, their collective opinion became more strongly against it.