Facts About Human Hibernation: Our Ancestors May Have, Will We?

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A preliminary study suggests our ancient ancestors entered hibernation. During the cold winter months, they took to hibernacula in caves and slept through the winter. Now, their fossilized remains have left behind clues showing they may have suffered considerably while hibernating.

This year, most of us might warm to the idea of hibernating through the winter. Due to the Coronavirus pandemic, we’re socially isolating and cooped up indoors. So, the concept of just sleeping until the pandemic subsides might sound ideal.  

However, judging by the scientists’ findings, hibernation was dangerous, leading to many health problems. Nevertheless, scientists are researching hibernation, suggesting that one day we might hibernate. In the future, hibernation could enable us to survive a new challenge: space travel.

Sima de los Huesos, the Chasm of Bones

The Sima de los Huesos is a cave in north-central Spain in the Atapuerca Mountains Translated; it means “the chasm or pit of bones.” The caves have revealed 28 individual hominid fossils now firmly dated to 430,000 years old. However, archaeologists found thousands of hominin skeletal remains.

Thus, it’s the largest and oldest collection of human remains in Europe discovered. Long before modern humans, Homo sapiens, evolved, early hominids such as Neanderthals and Homo heidelbergensis lived in the caves.

In March 2008, a jawbone dating to 1.2 million years ago was found in the area. The jawbone belonged to the species Homo antecessor, or the “pioneer man.” The species might have been a common ancestor of the Neanderthals and modern humans. 

See more about the archaeological site of Atapuerca from UNESCO below:

Hibernation in the Glacial Period

When our early ancestors inhabited the caves, it was during a glacial period. For months, they struggled to get through long, dark winters. Upon studying their remains, the researchers found signs they may have been able to survive through hibernation.

If primitive mammals and primates can hibernate, then perhaps the early hominids could also.

“The notion that humans can undergo a hypometabolic state analogous to hibernation may sound like science fiction, but the fact that hibernation is used by very primitive mammals and primates suggests that the genetic basis and physiology for such a hypometabolism could be preserved in many mammalian species including humans,” the researchers write.

During hibernation, mammals’ heart rate, breathing, and metabolic rate slow down. During this time, no water is required, and the body temperature is lower. By entering hibernation, mammals survive by expending the least amount of energy possible. Sleep continues without breaks to drink or look for food.

Evidence of Hibernation Preserved in Bones 

Although the early humanlike ancestors are long gone, their bones tell their story. After hiding out for months in the caves, abnormalities caused by disease and nutritional deficiencies left their mark.

Studying the bones required many techniques such as macrophotography, microscopy, histology, and CT scanning. 

Some of the health problems indicated:

  • renal rickets
  • brown tumors
  • osteitis fibrosa
  • rotten fence post 
  • beading of ribs 
  • secondary hyperparathyroidism
  • Chronic Kidney Disease
  • renal osteodystrophy 
  • Mineral and Bone Disorder 

In adolescents, there was evidence of annually intermittent puberty and healing due to “non-tolerated hibernation.” While they might have a growth spurt in the warmer months, their bodies didn’t fare well for the cold months.

Thus, it appears that hibernation proved challenging but allowed survival during an inhospitable glacial period. After hibernating, there was damage to bones and the onset of diseases due to poor nutrition and no sunlight exposure. Without the sun, there were vitamin D deficiencies.

Torpor, Brumation, and Estivation

Every year, warm-blooded mammals like bears get through the winters through long periods of extended torpor. During this time, it’s like a long winter nap rather than true hibernation. Usually, bears can respond if disturbed and occasionally takes breaks to drink or eat. On the other hand, hibernating mammals may only awake sporadically until warmer weather arrives.

Nevertheless, if the period of torpor lasts longer than 24 hours, it’s generally considered hibernation. 

Torpor

Some animals involuntarily go into torpor when the weather turns cold. These periods may last only a few minutes or for hours. Animals like birds, raccoons, skunks, and rodents can survive the winter through torpor. Bears are also considered to enter a state of torpor, though most people think of them as champion hibernators.

When animals awake from torpor, they may need to shake to get the muscles working again.

Below, a hummingbird sleeps in a state of torpor via Barticuno:

Brumation

Some cold-blooded animals brumate during the winter. Unlike hibernators, these animals rely on their environment to regulate their body temperature. So, they go into brumation and wake up depending on the outside temperatures. If it gets warmer, they will wake up for a break, regardless of the time of year.

Examples of species that brumate include many frogs, snakes, turtles, and reptiles like the Argentine Tegu and bearded dragons.

Today, reptiles like the Tegu are spreading throughout the American south, brumating in the colder months.

Estivation or Aestivation

What makes estivation, also called aestivation, different? It’s a survival strategy for conserving energy and water during hot and dry months. Thus, the period of dormancy tends to happen in the summertime. By going into estivation, animals can stay cool and prevent drying out, called desiccation.

Diverse animals take advantage of estivation, including some examples of:

  • Crocodiles
  • Snails
  • Fish
  • Frogs
  • Crabs
  • Moths
  • Ants
  • Beetles
  • Salamanders
  • Mosquitos
  • Tortoises
  • Dwarf Lemurs
  • Hedgehogs

As with torpor, animals estivate can wake up faster than if they were hibernating. Sometimes, they can reverse their short nap in only a few minutes.

Should Humans Revisit the Whole Hibernation Idea?

Through hibernation, torpor, brumation, and estivation, animals can survive. Now, it appears our ancient ancestors may have done the same.

Now, scientists must answer the question: Why did our ancient ancestors, which may have hibernated, die out? What allowed Homo sapiens the evolutionary advantage, though we can’t hibernate today? Maybe it’s time we revisit the whole concept?

For example, if we begin journeys into space, hibernation could prove a key advantage. Today, scientists are studying animals like bears to see how they do it. One day, it’s possible they may apply what they learn to induce humans into a state of hibernation.

By hibernating, humans could travel to new worlds.

See more about possible human hibernation during space travel from WIRED:


Featured image: Screenshot via YouTube/WIRED