What's important about that date, about 770,000 years ago, is that this was a glacial period on Earth, and Peking Man was found in far northern China.
That suggests he was probably the oldest cold weather inhabitant in human ancestry, said study co-author Darryl Granger, an atmospheric scientist at Purdue University whose research appears in Thursday's edition of the journal Nature. The average yearly temperature at the time in that part of China - at Zhoukoudian near Beijing - hovered around the freezing mark, but it was too dry for an ice sheet, he said.
Think of living in a "dry windy cold" much like winters in Calgary, Canada, without warm close-fitting clothes and well-made buildings to keep you warm, he said. And these inhabitants may not have even been able to warm up with a fire whenever they wanted either.
"They may have been freezing their buns off," said Rick Potts, a Smithsonian Institution human origins expert who wasn't part of the research. The research also demonstrates just how "wimpy" modern humans are, he said.
This raises a fundamental question. How did Peking Man survive the cold weather?
Potts raised three possibilities:
-Fire. Early findings showed signs of a fire in Peking Man's cave. But there has been debate about whether the fire was accidental or controlled, and evidence doesn't point conclusively either way.
-Fur. There is no evidence that this human ancestor used crude tools to make more form-fitting clothes. Loosely worn animal fur is more likely.
- Homo erectus had evolved to handle the cold.
It's that last part that is the most intriguing, Potts said. Just like the more modern Neanderthal, Peking Man may have had physiological changes that allowed more blood to flow to his extremities, he said.
"People in general who live in colder climates tend to be shorter and squatter," Potts said.
These aren't the oldest human ancestors in Asia, but it's the time period and the northern locale that intrigues experts.
The study authors were able to put Peking Man in colder weather because of a new method of dating the cave where the fossils were found. Many of the Peking man specimens were mysteriously lost after World War II. So Granger and his colleagues used quartz and other material that was found buried with the fossils.
The usual methods for dating - carbon-14 or uranium - don't go back far enough time, so the scientists looked at the ratio of aluminum to beryllium, which decay at different rates to come up with the new dates, Granger said.
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