A blueprint for hibernation
Deep inside Atxurra cave, some 300 meters from the entrance, the walls hold ancient art and more. They contain the physical records of a species that disappeared 24,000 years ago: the cave bear, Ursus spelaeus. For thousands of years, these animals used the cave's dark recesses as hibernation dens. In the soft clay and on rock surfaces, they left behind thousands of claw marks as they prepared their nests. These are not random scratches; they are a 16,000-year-old biological dataset.
Analysis of these claw marks reveals the bears' physical condition. Deeper, wider scratches were made by powerful, well-fed bears just entering their winter slumber. shallower, thinner marks show—one of bears emerging months later, emaciated. By measuring these differences, scientists can reconstruct the deep physiological changes the bears underwent. The data indicates a staggering 40% loss of body mass during a single hibernation cycle. This feat was achieved through extreme metabolic suppression, a state of reduced biological activity that modern science aims to replicate.
The cave itself is a significant archaeological site. Though known since 1929, its most important secrets were only revealed in 2015, when archaeologists and speleologists discovered at least 70 distinct works of Paleolithic art. These engravings and paintings of bison, horses, and goats date to between 12,500 and 14,500 years ago, created long after the cave bears had vanished. One panel famously depicts a bison pierced by nearly 20 spears, far more than in typical hunting scenes.
From deep caves to deep space
The metabolic control of the cave bear is of intense interest to researchers planning long-duration human space missions, such as a journey to Mars. An astronaut's body in microgravity suffers from muscle atrophy and bone density loss; for example, astronauts on the Mir space station lost 1-2% of their bone mass each month. Bears, however, can remain inactive for up to seven months without significant muscle or bone degradation. Their heart rate can drop from 55 beats per minute to just 14.
If humans could induce a similar state of hibernation, it would solve multiple logistical and medical challenges of spaceflight. Reducing an astronaut's metabolism would drastically cut down on the required food, water, and oxygen supplies. It would also mitigate the health risks of prolonged immobility and could potentially offer protection against cosmic radiation. The scratches in Atxurra cave are fossil traces; they are a tangible record of a biological superpower that could one day carry humans to other planets. The physiology that allowed Ursus spelaeus to survive icy winters thousands of years ago provides a blueprint for humanity's future in space.