A number of leading dance companies and schools, including Ballet Theater, have begun new efforts to increase diversity in classical ballet, but there is a long way to go. Jennifer Homans, the author of “Apollo’s Angels,” a history of ballet, said that ballet had fallen far behind other art forms, like theater, in that regard — making what she called the “phenomenon” of Ms. Copeland all the more important.

“What she has come to represent is so important in the dance world, and in the ballet world in particular,” said Ms. Homans, who is the director of the Center for Ballet and the Arts at New York University. “I think it’s about time. But I don’t think it’s enough.”

This history made Ms. Copeland’s chances for promotion a much-discussed topic in the dance world, and put a rare public spotlight on Ballet Theater as it weighed the kind of personnel decision that, in the rarefied world of ballet, is seldom talked about openly. That race could still be such an issue in 2015 — and that African-Americans could remain so rarely seen in elite ballet companies — has been depressing to many dancegoers, and has led to impassioned discussions in the dance world and beyond about race, stereotypes and image.

The dearth of black women in top ballet companies has been attributed to a variety of factors, from the legacy of discrimination and lingering stereotypical concepts of what ballerinas should look like to the lack of exposure to ballet and training opportunities in many communities.

Image Ms. Copeland was featured on one of the five different covers for Time magazine's “100 most influential people” issue.

More than a half-century has passed since the pioneering black dancer Arthur Mitchell broke through the color barrier and became a principal dancer at New York City Ballet in 1962, and a generation has elapsed since Lauren Anderson became the first African-American principal at Houston Ballet, in 1990. But City Ballet has had only two black principal dancers, both men: Mr. Mitchell and Albert Evans, who died last week. Ballet Theater officials said that the company’s only African-American principal dancer before now was Desmond Richardson, who joined as a principal in 1997.