From Sunday's New York Times article Ten Days That Changed the World:
MARCH 2, 1955: Almost a Heroine
When a brave young African-American woman was arrested for refusing to give up her seat on a Montgomery, Ala., bus, local and national civil rights leaders rallied to her cause. Claudette Colvin, 15, seemed poised to become an icon of the struggle against segregation. But then, shortly after her March 2 arrest, she became pregnant. The movement's leaders decided that an unwed teenage mother would not make a suitable symbol, so they pursued a legal case with another volunteer: Rosa Parks.
That switch, says the historian Douglas Brinkley, created a delay that allowed Martin Luther King to emerge as a leader. He most likely would not have led the bus boycott if it had occurred in the spring instead of the following winter. "He might have ended up as just another Montgomery preacher," Professor Brinkley says.