- Hey, smart people.

Joe here.

You ever heard that turtles can breathe through their butts?

- Turtles can breathe through their butts.

- Well, that's not really true.

When turtles are locked under the ice hibernating over winter with no way to surface and breathe air, they actually absorb oxygen through their skin.

There are a tiny handful of turtle species in Australia that can absorb oxygen through their you-know-whats though, so the snowman didn't completely lie to us.

But turtles are an example of how nature's had to come up with some crazy ways to survive harsh winters.

This lemur reduces its heart rate from over 300 beats per minute down to 6 and can go 10 minutes without breathing.

And don't even get me started on bears.

They don't eat for months during winter, so they recycle nutrients in their pee to keep their muscles from wasting away before spring.

What?

Turns out there's a ton of animals that are able to put their biology on slow-mo to survive in the cold or when resources are scarce.

But if all these other animals can fast forward through winter by slowing down or pressing pause, why can't we humans hibernate?

Think of all the potential benefits like extensive nap time, no more shoveling snow, interplanetary space travel.

But seriously, figuring out how to help humans hibernate might be a key to going where no human has gone before.

So let's explore what hibernation is and what it isn't, so that you can appreciate the incredible creativity of nature when it comes to surviving, and to find out if fat bears and sleepy squirrels might hold the secret to becoming an interplanetary species.

(upbeat music) Winter's a tough time to be an animal, okay?

It's really stinking cold, so they have to burn even more calories to stay warm.

But the days are shorter and food is scarce, so if animals are gonna outlive and outlast until spring, they really have three options.

One, they can push through and keep hunting for food throughout the winter months.

Two, they can leave winter behind by migrating or moving to another warmer habitat.

Or three, they can dig in and ride out winter by slowing down the processes of life: hibernation.

Let's get a few things straight before we look at all the ways animals slow down life and go dormant.

Now, pretty much every animal that goes dormant does this by slowing down their metabolism, ratcheting down how much energy they burn inside their cells, and also by slowing down their bodily processes.

That means a slower heartbeat, slower breathing, and a lower body temperature.

Now this sounds like deep sleep, but it isn't.

Think of it like this.

Sleep is like keeping your car's engine running even if you aren't driving it, because keeping the engine warm makes it easier to hit the road again when you wake up.

What these animals do is like turning the engine off.

It saves energy, but it takes longer to rev up.

There are lots of different types of dormancy that can last from days to months.

For instance, many hummingbirds enter a state called torpor every night so they don't starve to death.

Hummingbird metabolism is absolutely nuts, okay?

During the day, hummingbirds have to eat every 10 minutes to stay alive.

The equivalent of a human eating 155,000 calories a day.

What?

But at night, hummingbirds can't really feed, and since it's cooler when the sun's down, they have to burn more energy to stay warm anyway.

So at night, hummingbirds drastically reduce how much energy they burn, sometimes lowering body temperature by as much as 50 degrees.

Other animals enter estivation.

It's a type of slowdown that happens during extremely hot and dry periods, like water-holding frogs which cocoon themselves in mucus and bury themselves alive to slow down water loss.

It's a living.

And then there's brumation, unique to some reptiles.

Ectothermic animals like these scaly boys, they rely on external heat to maintain their body temperature.

And since ectothermic animals can't generate their own body heat, cold temperatures force them into a sluggish, lethargic state, kind of like a teenager on Saturday morning.

Their cells cool and the machinery of life slows down, sort of how it's harder to stir peanut butter out of the fridge versus at room temperature.

Many reptiles use dens or burrows to protect themselves during brumation, but others like wood frogs stay near the surface, basically turning into frog popsicles thanks to special compounds in their blood that work like antifreeze to protect their cells from damage by ice crystals.

But mammals do winter dormancy a little differently: through hibernation.

It's kind of torpor on steroids.

For starters, hibernation is limited to animals that produce their own body heat, so reptiles need not apply, and it's almost exclusively seen in mammals.

Aww.

Hibernation is triggered when the days get shorter, temperatures cool off and food becomes more scarce.

Also, when pumpkin spice lattes hit Starbucks.

Scientists believe this fires up special neurons in the animal's hypothalamus, which controls functions like hunger, metabolism, body temperature, heart rate, breathing, and sleep.

Basically all the bodily functions that change during hibernation.

Now, those neurons send chemical messages in hibernators' blood, telling the body it's time to slow down.

Now, exactly what kicks off hibernation is still a bit of a mystery, but we know a lot more about what changes happen next.

Leading up to hibernation season, these animals have usually been eating a lot.

Looking at you here, fat bears.

And those extra calories are converted to brown fat.

Brown fat is full of mitochondria- The powerhouse of the cell.

Wow, I didn't know we still had that animation.

Well, all those mitochondria make brown fat better at producing heat when the fat is burned, which helps mammals stay warm without relying on more energy-intensive things like shivering.

Many hibernators drop their body temperatures by an average of 5 to 10 degrees Celsius.

The biggest swing happens in Arctic ground squirrels.

They go from a 37 degree body temperature to as cold as minus three degrees.

Every once in a while during hibernation when things get too chilly, these squirrels and other hibernators briefly stir to shiver, burn more fat, and then it's back to hibernation.

And that's one misconception about hibernation.

Even though it lasts for months, most hibernators do wake up occasionally.

Scientists think maybe their immune systems need to turn on to deal with a germ or because they simply get too cold like our squirrel friend.

Ironically, research shows hibernators don't actually sleep.

So if you ever come across a bear in springtime, keep in mind they're probably pretty cranky.

By now you're probably wondering about bathroom breaks, and I don't blame you.

Since the whole point of hibernation is slowing down metabolism, hibernating animals don't really produce much waste.

Some hibernators may release tiny amounts of waste during their chill, but more often they just recycle that water and waste back into their bodies.

Bears famously don't pee or poop all winter, even building up this hard, dried fecal plug in their colon to act as, well, a lot like what the drain plug in the bathtub does.

Hibernation also comes with some pretty big benefits.

Small mammals are five times less likely to die when hibernating than when trying to last out the winter.

And a lack of movement and smell makes it harder for predators to find hibernating prey, and hibernators even live longer than non-hibernating species of the same size.

While science isn't exactly sure why, studies on marmots suggest that hibernating could slow down the aging process.

So feel free to add that to your self-care routine.

Which brings us to an interesting question: why don't humans hibernate?

And could we?

Now, unfortunately, hibernation is not really in the human repertoire.

Humans evolved in Africa, a continent that's not exactly famous for igloos or skiing.

And because humans are omnivorous, we had year-round food choices.

So with no winters or severe food shortages, hibernation just wasn't something we had to evolve to do.

But the biggest reason humans don't hibernate is our brains.

Instead of evolving to hibernate, we became problem solvers.

Winters get too cold?

We'll make clothes and fire.

Not enough food?

No worries, we'll learn how to store food to eat it later.

And if things get too bad, we'll just pack up and migrate.

No hibernation necessary.

Not only that, hibernation causes cognitive loss.

During hibernation, mammals lose half to two thirds of their brain's synapses.

Like, bears have to relearn certain smells after hibernating.

But while humans don't hibernate now, some of our ancient ancestors may have hibernated around half a million years ago.

That means the genetic programming for hibernation might be lurking around in some ancient part of our DNA.

Scientists are working to crack that code, because figuring out how to put humans in hibernation could help us treat traumatic injuries and severe illnesses by sort of slowing down time inside the body.

It could also help us live longer thanks to the anti-aging benefits seen in some hibernators.

And perhaps most interestingly, it's an important tool we might need for space travel.

The nearest potentially habitable planet to Earth orbits the star Proxima Centauri, and getting there using current technology would require a more than 6,000-year journey.

That's why NASA started researching the possibility of human hibernation in 2014.

The research started with what we already know, that cold temperatures can slow down human metabolic processes just like other mammals.

We already use therapeutic hypothermia in certain health emergencies like heart attacks, but it's a lot trickier and more dangerous to extend that process for weeks, months, or years.

While temperature can help slow down our metabolism, we have to figure out a way to keep our bodies from starving themselves in the process.

Hibernation also slows down our immune systems, making us more susceptible to diseases.

And remember how bears don't poop during hibernation?

Well, we would have to in order to avoid sepsis and other really nasty things.

So if you've got a solution to that, call NASA.

These are obviously big hurdles for science to overcome, and yet NASA's study found that there aren't really any fundamental biological reasons humans couldn't hibernate.

It's just that our technology hasn't caught up with the problem yet.

And maybe when it does, we'll be one step closer to a future napping like fat bears amongst the stars.

Stay curious.

That last one's not yet proven.

What is, what?

What are these words?

What am I doing?