Hibernation: Not Just for Animals?

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Why isn’t crawling into bed like a well-fed grizzly bear and sleeping away the world’s problems on our list of options for surviving life? I imagine my hibernation pod would be kind of like the COVID-19 pandemic’s “stay-at-home” orders, but with a lot more sleep and a lot less pizza delivery (though adequate snacks would still be essential).

Every year when the season is unseasonable, scores of animals find safe places to slow their bodies down to a torpor—an extended sleep-like state in which body temperature and metabolism decrease to help animals survive times when food is scarce.

When I think of animals that undergo torpor, I picture fat bears hibernating through the winter or Southern Arizona’s desert spadefoot toads burrowing deep into the desert floor. The toads brumate—brumation is a form of torpor that amphibians and reptiles go through—for most of the year until the monsoon rains signal that they can come out for a few weeks to eat, drink and mate. Many of us know that bears, toads, bats and turtles practice torpor, but we don’t usually picture humans on the list of known hibernators. However, the study of a 500,000-year-old population of extinct ancestral humans called hominins suggests that they may have hibernated to survive times when resources were limited.

This hominin population—found in Sima de los Huesos (the Chasm of Bones) in Atapuerca, Spain—lived during a time when Earth was covered in glaciers. This climate caused seasonal periods of cold and limited food availability. Study of the fossils reveal a tell-tale signature on the bones that suggest the Sima de los Huesos population had diseases associated with torpor, such as reduced calcium in the bones. When nutrient stores were not enough to support proper bone and tissue growth during torpor, there were periods of slowed bone growth sandwiched in between periods of growth and healing.  

Marks of these nutrient deficiencies are permanently written on the skeletons of our human ancestors and tell a story that suggests our ancestors practiced torpor to survive harsh winters.

Our bodies are equipped to handle periods of long-term stress by making hormones that send signals from the brain to the adrenal glands. The adrenal glands release cortisol, which tells the body to make nutrients such as fats and sugars readily available during long-term stress situations—like long, cold winters.

So, if an animal doesn’t take in enough available nutrients before it goes into torpor, its body will draw from its own reserves. When the sugars and fats are gone, muscles become a source of energy, and bones and teeth are broken down for calcium. This tells us that although humans and animals adapt to hibernation, those adaptations are not without tradeoffs.

Even so, I can’t help but wonder if human hibernation pods could be part of our future.

Lisa Ganser, PhD, is a health communications specialist for the Alaka’ina Foundation Family of Companies in Atlanta. She was formerly a vertebrate physiologist for Kennesaw State University in Kennesaw, Georgia, where she taught human physiology, comparative vertebrate anatomy and ecophysiology courses. Ganser enjoys working with the public—especially indigenous populations and tribal communities—and finding new ways to help her community through science.

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