During the cold months of winter, for most animals, the supply of food becomes scarce, for some animals the food bases even disappear completely.

In order to survive anyway, some species have developed a strategy that allows them to bridge the frosty and barren weeks: in the fall they retreat into caves, holes or foliage and sleep with some interruptions until the temperatures begin to rise again in spring.

To prevent themselves from starving during these months, they lower their body temperature to a few degrees above zero, slow their heart and respiratory rate as well as all other metabolic activities to a minimum and consume exclusively from their eaten fat reserves.

When thinking about hibernation, humans are not the first things to come to mind. Switching to a power-saving mode is not available to us – is it?

Researchers have now discovered evidence in the bones of a primitive species that at least some of our close relatives may have developed a comparable survival method several hundred thousand years ago to make it through extremely cold winter months.

The bones in question come from the Sima de los Huesos in Burgos in northern Spain. Over the past three decades, thousands of teeth and pieces of bone have been uncovered in the cave at the bottom of a 15-metre-deep shaft, including the remains of several dozen early Neanderthals or their immediate predecessors, who may have been deliberately dumped there.

The cave thus is akin to a mass grave more than 400,000 years old and is considered one of the most important paleontological treasuries on earth.

Hundreds of human bones have been found in the Sima de los Huesos in the past. Some of these showed traces that researchers associate with the consequences of hibernation.

What a group led by Juan-Luis Arsuaga of complutense Madrid University discovered when analyzing some of these fossils had previously been known only from the bones of hibernation-holding animals: characteristic lesions and seasonal variations, from which one can conclude that bone growth is disturbed over the course of several months of each year.

One possibility, therefore, is that these early humans repeatedly temporarily reduced their “metabolism in such a way that they could survive for a long time in extremely cold conditions and with very limited food supplies with enough body fat,” as the team reports in the journal L’Anthropologie. In other words, they were in a kind of hibernation, which manifested itself as a disturbance in bone growth.

The researchers admit that this may sound quite adventurous, but point to some primates, such as the fat-tailed lemurs in Madagascar, which regularly hibernate during the dry season between April and October. “This suggests that the genetic basis for such hypometabolism could also exist in humans,” Arsuaga says.

It should come as no surprise that this idea is causing controversy in professional circles: Chris Stringer of the Natural History Museum (London), for example, points to the high energy hunger of the human brain, which would prove to be a problem. “However, the idea is fascinating and should be further studied on the basis of the genomes of primitive humans,” says the paleoanthropologist.