Humans did not evolve to hibernate for many reasons. But genes from our ancient ancestors may mean that the possibility is within us. In fact, human hibernation could help advance medical and astronautical science.

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On long winter days when it feels too icy, gray, and cold to move, you may wonder why humans can’t make like bears and hibernate. Wouldn’t that be a great way to get through a long winter full of too-early, too-chilly mornings?

And couldn’t we use human hibernation to survive trauma or illness or even explore space?

The answer is complicated.

Here’s what to know about why humans do not hibernate (yet) and why some scientists and researchers believe it’s only a matter of time until we do.

There isn’t much good evidence for human hibernation of any kind.

A British Medical Journal story from 1900 claimed to show a form of human hibernation in Pskov, Russia, called winter sleep, or “lotska.” But current researchers say there’s no evidence to show it’s anything more than a story.

The 2000 reprint of the article paints the picture of Russian peasants who spend half the year asleep to avoid the hardships of chronic famine. The unknown author says that family members take turns tending a fire while the other members sleep. They wake up once a day to eat a slice of bread, go back to sleep, and rouse months later when the weather warms.

Avoiding the harsh winter cold does sound pretty good. But not so fast…

Dr. Sandy Martin, an expert on hibernation and professor emerita at the University of Colorado, says she hasn’t seen convincing evidence of human hibernation or the Pskov winter sleep.

She would, she says, love to see a physiological study of this type of practice because it might be vital to reproducing human hibernation.

“If these people are still doing that, yay! Let’s study them,” says Martin. “I’ve never heard of anything like this in 40 years of hibernation meetings. What I have heard of is [Aboriginal people] sleeping naked outside in near-freezing conditions. But that’s not hibernation. It’s one night.”

So, humans don’t hibernate. Yet.

That’s a good question with some evolutionary answers.

Very long ago, one of our prehistoric ancestors did hibernate. This ancestor was the predecessor of all mammals, including humans. Some people believe this means that science can induce humans to hibernate once more.

“In my opinion, hibernation is the primal trait,” Martin explains. “Maybe we survived the great asteroid extinction because our relatives could use hibernation for that time. Maybe we were underground, pre-radiation mammals. Evolutionary genetics say that the common ancestors of all mammals were hibernators.”

Research from 2020 suggests that early humans may have been able to hibernate. While the findings are inconclusive, researchers suggested that these ancestors from half a million years ago may have hibernated to survive extremely cold conditions.

“I think it’s an ancestral trait we’ve lost,” Martin adds. “That means that we have the genes we need to hibernate.”

Martin thinks that means it’s only a matter of time before we can figure out how to hibernate. So why don’t we do it naturally?

According to Martin, humans probably do not hibernate because it was not to our evolutionary advantage. It would not have promoted survival and reproduction.

Here are some reasons why:

  • Being in torpor (shutting down your metabolism) or hibernation (prolonged torpor) would mean you are unable to reproduce.
  • If you’re not reproducing, it means other competitor species are reproducing more than you and possibly taking your place.
  • When you’re in torpor, you cannot defend yourself from predators.

“It’s an evolutionary trade-off. And, you lose in the sense of success unless you are a species using torpor in a very safe place,” Martin said.

Researchers are looking at different ways to usher humans into hibernation.

Controlled hypothermia

Medical professionals already use therapeutic hypothermia, which is a way of lowering your body temperature. This slows down your metabolic processes like blood circulation and breathing.

Healthcare professionals use therapeutic hypothermia to treat at-risk people, such as people who have experienced physical trauma, those receiving a transplant, and some people undergoing surgery.

Martin says medical hypothermia isn’t the same as torpor or hibernation. Yet some researchers believe people might one day be able to hibernate using a form of controlled hypothermia.

Degrees of torpor

Another approach might be finding a way to trigger the same processes other mammals use to reach torpor. But it’s not clear yet how we can do that. Researchers are still trying to identify and understand all the complex mechanisms that enable animal hibernation.

Different animals achieve torpor and hibernation in different ways, temperatures, and circumstances.

Many small mammals, such as bats, mice, and lemurs, go into torpor daily. Other mammals can hibernate for 6 months through autumn and winter. In a study from 2007, a marsupial called the pygmy possum was able to hibernate for up to a year in laboratory conditions.

Martin co-wrote a 2015 article on the hibernation continuum. It suggests that there are different stages of metabolic activity. The extremes of this continuum are activity at one end and hibernation at the other.

Another theory is that we can achieve hibernation via slow-wave sleep, which lies in the middle of this continuum. Humans naturally experience slow-wave sleep every night. Slow-wave sleep lowers your metabolic rate and body temperature.

Torpor vs. hibernation

Torpor: This is when an animal shuts down its metabolic processes, such as breathing, circulation, and energy use. A key element of this is lowering their body temperature to below 91ºF (33ºC). Torpor is typically short-term, lasting fewer than 24 hours.

Hibernation: This is a prolonged period of torpor that animals use to survive seasonal changes in temperature or food scarcity. It’s torpor that lasts longer than 24 hours and can range from a few days to several months. Body temperatures can drop to -27ºF (-3ºC) and save up to 90% of their energy.

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According to several studies, human-induced torpor or hibernation could be significant for space exploration and medicine.

Being able to sleep for long periods would cut down on the stress of space flight and stretch valuable life support resources. This would allow humans to travel long distances to distant places such as Mars and its moons.

Being able to hibernate could also help you survive intense surgeries, including organ transplants. Healthcare professionals might better treat cancer tumors if they could put people into a state of torpor. People who have experienced physical trauma might also have a better chance of surviving until medical staff can effectively treat their injuries.

Medical applications

Animals safely lower their blood pressure, body temperature, breathing, and other processes through natural hibernation. Hibernation could help humans survive life threatening emergencies like heart attack, stroke, and blood loss. It could also help organ transplant recipients.

Currently, healthcare professionals can induce hypothermia. Still, that’s not the same as torpor or hibernation.

A 2018 review of research suggests that torpor or hibernation may:

  • increase resilience during transplant surgery
  • prevent muscle wasting and osteoporosis in people with limited mobility
  • prevent entire body or single organ shock
  • cause cancers to be dormant until better treatment options are available

Space exploration

In a 2017 article, researchers considered the potential benefits of torpor for human space flights to Mars and its moons. The authors proposed that torpor induced through therapeutic hypothermia could:

  • cut down on the use of life support and other resources
  • reduce water and food intake by up to 75%
  • reduce waste production
  • protect against radiation
  • ease psychological concerns associated with long-term space flight

Torpor could also act as a buffer to the stress of being confined with several other people over long periods, such as on a crewed space flight.

Getting humans into torpor or hibernation is one thing. Getting them safely out of it is another. Researchers are not yet sure how to do that. Much more research is needed to understand how mammal bodies go into and safely come out of torpor.

In animal studies, brain activity in hibernating mammals differs from sleep, coma, or anesthesia. Some researchers believe we should understand more about this state in humans.

Martin says that there are also possible cardiac issues.

“People’s hearts don’t do well when they get cold,” Martin said. “That’s a real and immediate risk. We have to understand why human hearts fibrillate and can’t make successful contractions.”

A NASA-funded proposed protocol for the use of human hibernation for space travel suggests other risks as well:

Martin cautions, “I think we need to know a whole lot more about the mechanisms that underlie hibernation before we can say humans are capable of hibernation.”

There is no evidence that humans can go into hibernation, an extended state of torpor.

Torpor is the physiological state of metabolic depression, in which your body temperature, breathing, and energy expenditure drop.

But humans have distant ancestors that did hibernate. Some researchers believe we may still have the genes to hibernate. There has been much research into how other mammals hibernate and how we can apply that knowledge to humans.

Science has not unlocked all the secrets yet. Still, some researchers believe it’s a matter of time until humans can safely go into torpor or hibernation. If so, we may be able to explore more distant regions of space and even receive more effective medical care here on Earth.