Bears do it. Bats do. Even European hedgehogs do. And now it turns out that early human beings could have been at it too. They hibernated, according to fossil experts.
Evidence from bones found at one of the world’s most important fossil sites suggests that our hominid predecessors may have faced extreme cold hundreds of thousands of years ago sleeping through winter.
Scientists claim that the lesions and other signs of damage to the fossilized bones of the first humans are the same as those left in the bones of other hibernating animals. These suggest that our predecessors coped with the fierce winters of that time, slowing down their metabolism and sleeping for months.
The findings are based on excavations in a cave called Sima de los Huesos – the pit of bones – at Atapuerca, near Burgos, in northern Spain.
Over the past three decades, the fossilized remains of several dozen people have been scraped from sediment found at the bottom of the 50-foot dizzying tree that forms the central part of the Atapuerca pit. The cave is actually a mass grave, say researchers who have found thousands of teeth and pieces of bone that appear to have been deliberately thrown there. These fossils date back more than 400,000 years and were probably from the first Neanderthals or their predecessors.
Map of Burgos
The site is one of the most important paleontological treasures on the planet and has provided essential information on how human evolution has progressed in Europe. But now researchers have produced an unexpected turn of events.
In a paper published in the journal Anthropology, Juan-Luis Arsuaga – who led the team that dug the site for the first time – and Antonis Bartsiokas, of the Democritus University in Thrace in Greece, claim that the fossils found there show seasonal variations that suggest that bone growth was interrupted for a few months of each year.
They suggest that these early people found themselves “in metabolic conditions that helped them survive for long periods of time in cold conditions, with limited amounts of food and sufficient deposits of body fat.” They hibernate and this is recorded as disturbances in bone development.
Researchers admit that the notion “may sound like science fiction,” but point out that many mammals, including primates, such as bushes and lemurs, do so. “This suggests that the genetic basis and physiology for such a hypometabolism could be preserved in many mammalian species, including humans,” say Arsuaga and Bartsiokas.
The pattern of lesions found in human bones in the Sima Cave is consistent with lesions found in the bones of hibernating mammals, including bears in the cave. “A hibernation strategy would have been the only solution to survive, having to spend months in a cave due to frozen conditions,” say the authors.
It also indicates that the remains of a hibernating cave bear (Ursus pa) were also found in the Sima pit, which makes it all the more credible to suggest that humans do the same “to survive freezing conditions and food shortages as cave bears”.
The authors examine several counterarguments. Modern Inuit and Sami people – although they live in equally harsh and cold conditions – do not hibernate. So why did the people in Sima Cave do it?
The answer, say Arsuaga and Bartsiokas, is that fatty fish and reindeer fat provide food for Inuit and Sami people in the winter and thus prevent the need for them to hibernate. In contrast, the area around the Sima site half a million years ago would not have provided anything like enough food. As he states: “The aridification of Iberia then could not have provided enough high-fat food for the inhabitants of Sima during the harsh winter – making them resort to hibernating the cave.”
“It’s a very interesting argument and will certainly stimulate debate,” said forensic anthropologist Patrick Randolph-Quinney of Northumbria University in Newcastle. “However, there are other explanations for the variations observed in the bones found in Sima and these must be fully addressed before realistic conclusions can be reached. I don’t think that’s done yet. “
Chris Stringer of the Museum of Natural History in London pointed out that large mammals, such as bears, do not actually hibernate because their large bodies cannot reduce their base temperature enough. Instead, he falls into a less deep sleep known as drowsiness. In such a state, the energy requirements of the human-sized brain of Sima people would have remained very high, creating an additional problem for them to survive during the torpor.
“However, the idea is fascinating, which could be tested by examining the genomes of the Sima people, Neanderthals and Denisovans for signs of genetic changes related to the physiology of torpor,” he added.