A Long Winter’s Nap: Humans, Hibernation, and Some Really Old Bones

Winter offers endless delights: sledding and snow forts, animal tracks criss-crossing the snowy forest floor, and countless excuses for hot chocolate. But the delights often come with biting wind and painfully cold fingers. Winter can become too much of a good thing, and many of us are eager for spring far before it arrives.
Some animals, like groundhogs, bats or bumblebee queens, skip the season altogether by hibernating. They nestle down in the fall and get ready for a season of inactivity by dropping their body temperature, metabolism, and breathing and heart rates. This allows them to conserve energy—their body fat, as long as they have enough of it, provides them the energy to survive until spring.
So it intrigued me to learn about hibernating humans. Humans! They were a different species from us Homo sapiens (Neanderthals? Homo heidelbergensis? That part’s still being worked out), and they lived over 400 thousand years ago in northern Spain.

Skulls from study site (Sima de los Huesos, northern Spain)

 

The fossilized bones of these ancient humans show patterns similar to those on bones of other hibernating animals. (Like those of the cave bear they found close by!) It appears that bone growth was interrupted each year while these early humans slept the winter away in caves. The fossils also indicate that they were hard-hit by diseases common to hibernating animals, such as kidney disease and bone deformations.
But it’s always been assumed that humans CAN’T hibernate. We’re too big, we need too much food, and we evolved in hot climates that wouldn’t require us to sleep for months at a time. And unlike hibernators, our bodies tend to stop working if they get too cold or stay still for months. And really, why would we bother? Humans have enjoyed fire and hunted large game for millions of years, so we don’t really need to hibernate, especially in an area as gorgeous as Spain. Right?

“Wrong!” say the researchers, who point out that these humans were living in one of the coldest, driest glacial periods of the last million years. The weather was brutal, there was little evidence of fire use (which didn’t become a regular thing for another fifty thousand years), and there wasn’t enough food to survive the winter. By contrast, other Indigenous peoples living in harsh climates, like the Inuit or Sami, could eat fish, seal, or caribou meat all year, so they never needed to hibernate.

The hibernating fat-tailed dwarf lemur shares 98% of our human genes. Its fat tail provides energy while it’s zonked out.

 

Not all scientists are convinced that the bones prove that humans could hibernate. But some other primates—our evolutionary cousins—sure can. The fat-tailed dwarf lemur for instance, with whom we share 98% of our genes. Why the fat tail? To provide it with energy while it’s zonked out for half the year of course! Whatever genetic basis there is for hibernation, it’s probably lurking somewhere in our genes. Convinced or not, many people are interested, and not just because some of us find winters a little long for our liking. NASA is researching the possibility of having astronauts hibernate for weeks at a time, in order to reduce the food and materials needed on long journeys to deep space.

Medical researchers are working on “inducing hibernation” in patients with severe trauma who are on the brink of bleeding to death. This would allow doctors extra time to examine patients, stop the bleeding, and perform surgery before bringing them back to, well, life.
All of this makes me appreciate how fascinating hibernation really is, was, and could be. But also, I’m now feeling awfully grateful that we don’t need to do it ourselves!

Anne Munier is a communications specialist in Ontario who finds wonder everywhere in the natural world. Anne’s writing is inspired by life — from the ecology of forests to the interrelationships of human communities. With a B.Sc. and M.Sc. in Biology, she’s worked in the fields of environmental research, climate change, and food security. When not exploring forest fungus, she might be found germinating seeds from interesting fruit, dancing on the beach with a flock of 9-year-olds, growing giant parsnips, or otherwise avoiding housecleaning.

Skull images used under CC BY-ND-2.0 license. Lemur image (C)
David Haring, used with permission of the Duke Lemur Center.