Just like the American black bear and the European hedgehog, early humans may have hibernated to endure severe winter months.

Animals hibernate to survive cold weather and reduced food access by decreasing their metabolic rate and body temperature for months at a time. Accustomed to our modern-day central heating and abundance of supermarkets, the prospect of human hibernation seems like science fiction. However, 430,000 years ago, Earth experienced a period of extreme glaciation — otherwise known as the Ice Age. New research from scientists in Spain suggests evidence that these brutally cold times may have led to hibernation.

Animal hibernation causes high levels of the hormone parathyroid in the blood. This chemical damages bones, leaving long-lasting tell-tale signs. In this study, paleontologists examined human specimens for hyperparathyroidism from the Sima de los Huesos cave — Spanish for "pit of bones." The burial site is home to over 7,500 human fossils, from 29 individuals, between 300,000 and 600,000 years old — making it the largest and oldest collection of human remains to date.

The team studied the bones using a combination of microscopy and CT scans — the same as those used in hospitals. They discovered a plethora of lesions and bone damage indicative of disorders such as rickets, Chronic Kidney Disease — Mineral and Bone Disorder (CKD-MBD) and hyperparathyroidism. The authors propose that these diseases were caused by poor toleration to hibernation.

They argue that these ancestors may have hibernated for up to four months at a time. This strategy was imperative for survival during frigid and food-scarce periods, such as the extreme glaciation 430,000 years ago where these individuals lived.

While this discovery is certainly exciting, it is not entirely conclusive. Fossil experts will likely continue gathering more research to determine whether early humans really did hibernate, or not.