As National Geographic editors prepared an issue dedicated to race, they realized the 130-year-old magazine might face questions about its troubled history on the subject.

So they asked John Edwin Mason, a University of Virginia professor who studies the history of Africa and photography, to dig through the magazine’s archives to examine its shortcomings in covering people of color in the United States and abroad.

He was unsparing.

“Through most of its history, National Geographic, in words and images, reproduced a racial hierarchy with brown and black people at the bottom, and white people at the top,” Mr. Mason said in an interview on Tuesday.