While social psychologists were interested in the uniformity of groups—that is, the way that group members act in concert—some psychoanalysts became interested in the interactions among group members. From working in clinical settings, these clinicians recognized that group dynamics influenced the ways people relate to each other. Specifically, they noticed the ways that group members formed alliances with each other, split into different factions, and aligned with, and then rebelled against, group leaders. Wilfred Bion (1897-1979) was a pioneer in this movement. Another influential clinician in the group therapy movement is the psychiatrist Irvin Yalom (1931-).