It's a provocative theory, one that the researchers themselves admit sounds farfetched. But their analysis of ancient bones from a cave in Spain suggests that early humans hibernated—or something close to it—through the winter, reports the Guardian. Scientists poring over skeletal remains dating back 430,000 years found that they bore the same telltale signs of hibernation as the bones of bears and other animals known to slumber through the winter, per Science Alert. Among the clues is evidence that bone growth was disrupted for months-long stretches. Also, hibernation is a tricky feat to accomplish, and when it doesn't go well, hibernators suffer from a particular set of ailments such as kidney disease. The bones show evidence of these, the researchers write in the journal L'Anthropologie.
"The notion that humans can undergo a hypometabolic state analogous to hibernation may sound like science fiction, but the fact that hibernation is used by very primitive mammals and primates suggests that the genetic basis and physiology for such a hypometabolism could be preserved in many mammalian species including humans," they write. The researchers note that in the area where the bones were found, early humans would have faced severe food scarcity and frigid temperatures throughout the winter. Hibernation, then, may have seemed a viable survival strategy. The Guardian talks to a forensic anthropologist who is intrigued and predicts the study will generate debate. But, he adds, "there are other explanations for the variations seen in the bones found in Sima and these have to be addressed fully before we can come to any realistic conclusions." (Read more discoveries stories.)