Dr. Reich and Dr. Skoglund reanalyzed the findings — but did not reach the same conclusions.

In the original study, Dr. Manica and his colleagues sought to understand how the ancient Ethiopian man (dubbed Mota, after the cave where his body was buried) was related to other humans. The researchers found many unique mutations that linked Mota to a group of Ethiopians who live near the cave today, known as the Ari.

By contrast, the researchers found that Mota was only distantly related to many people elsewhere in Africa. In fact, the analysis suggested that most living Africans shared some DNA with Europeans and Asians that were missing from Mota’s genome.

To explain these intriguing results, Dr. Manica and his colleagues tested out different historical scenarios. In the best-supported one, a group of people migrated from the Near East back to East Africa — a so-called backflow — about 3,000 years ago. In subsequent generations, their DNA spread across Africa.

But some of the implications of this theory were surprising. For one thing, this backflow seemed to have raged like a flood, spreading all the way across the continent in relatively little time.

Those provocative implications drew wide attention in the media, including The Times. Unfortunately, Dr. Skoglund and Dr. Reich couldn’t find any trace of the migration beyond East Africa.

Once Dr. Manica learned of the conundrum, he and his colleagues retraced their steps.

They discovered that they had neglected to take one small but essential step in their analysis. “It was clear human error,” said Dr. Manica in an interview. “It’s just something that should have been done that didn’t get done.”

The DNA in a bone thousands of years old has broken into little fragments. After scientists retrieve those fragments, they must fit the pieces back together like a jigsaw puzzle.