Tiya Miles, a professor of American culture and history at the University of Michigan, believes that Hollywood, fashion and beauty businesses are responding to the popular public movements demanding change in the wider global political and economic landscape.

“In reaction to a sharpening sense of white nationalist identity across America and Europe, there is a growing consciousness of the importance of visibility and vocality for people of color, particularly black people,” Ms. Miles said. “It is no coincidence that this runway model trend and movies like ‘Black Panther’ have arrived at the same time. The two are interlocked, as both have been incubating in what feels a like a growing crusade with many of the hallmarks of the Black Power movement of the 1960s and 1970s. They are part of a pushback against the dominant pressures of European and American white centrality.”

Patrizia Pilotti, a casting director for brands including Lacoste and Valentino, both of which featured higher than average numbers of models of color this season, suggested other factors were at play. In the digital era, she said, the frenetic cycles of fashion don’t apply only to clothes, but also to the models who wear them. The pressure is on for brands to feature new faces, and so modeling scouts have been casting their nets farther afield in recent years, visiting new cities and territories in the quest to bring a more diverse offering to casting agents.

“I have never seen so many different girls on agents’ books as I did this season. But there is one reason I cast so many dark-skinned girls, and one reason only: their beauty,” Ms. Pilotti said. She was also emphatic that she was not adhering to any outside demands or quotas when it came to casting for those shows. “This season, for these collections, these girls are the ones that spoke to me.”