The Insane Evolution of: Hibernation

the forests of Madagascar are filled with some of the world's most unusual species chameleons crawl through the trees and over strange volcanic formations the carnivorous fossa hunts rodents birds and ring-tailed lemurs and perhaps the weirdest of all are the fat-tailed drawer flemers with long tails and enormous eyes these nocturnal primates only weigh about 160 grams and live on a diet of fruits insects and small animals but that's only for half the year for the other six or seven months during the forest's dry season these lemurs hibernate in tree holes living off the fat stores in their tail their body temperature can fluctuate by as much as 20 degrees Celsius as the temperature outside their nests Rises and falls their heart rate breath rate and brain activity levels also drop precipitously and while hibernation is in no way the same as sleep hibernation can actually lead to sleep deprivation these little lemurs look pretty dead to the world in fact scientists recently discovered that two other species of dwarf lemur living in the High Altitude forests of Eastern Madagascar hibernate in underground holes protecting themselves from near freezing temperatures when the scientists uncovered their Burrows they found tightly curled up balls of fur the Lemurs deep in hibernation these miniature lemurs are the only known species of primate to hibernate but this seasonal switch to a decreased metabolism and reduced body temperature is widespread across the animal kingdom we see it in freshwater turtles ground squirrels bats and of course Bears it's an essential adaptation allowing species to survive frigid Winters and reduced availability of food not only that but species that hibernate actually have longer life spans than species of similar sizes that don't hibernate humankind has been aware of animals ability to hibernate for thousands of years going all the way back to ancient Greece and Aristotle but we're still unraveling the mysteries of how they do it without losing muscle mass bone density and brain cells Bears can survive without food for months at a time and some species of turtle go for over 100 days without breathing how do these animals manage such remarkable Feats where did hibernation even come from in their evolutionary history and could humans someday manage the same thing the story of hibernation begins hundreds of millions of years ago when Earth's land masses were all clumped together in one supercontinent called Pangea during this time a strange animal roamed the region that would become Antarctica and spread as far as present-day India and southern Africa the listrosaurus was a four-legged forager with tusks in its upper jaw generally growing to the size of a pig but sometimes reaching two and a half meters in length they are distantly related to Modern mammals although the planet was much warmer 250 million years ago the southern tip of Pangea was still in the Antarctic Circle and experienced long stretches without sunlight every year when researchers compared fossils of the listrosaurus found in Antarctica versus those found further north they made a surprising discovery growth patterns in the tusks of those who lived around the Antarctic Circle showed annual marks of stress that are very similar to what we see in modern day animals that go into hibernation those researchers hypothesized that this might be evidence of hibernation in some of our oldest mammalian ancestors the ability to hibernate seems strongly related to the way reptiles manage their body temperatures and metabolisms which is completely different from how mammals do it in Popular Science we think of reptiles as being cold-blooded but the technical term for them is ectotherms this means that they can't produce their own body heat and instead rely on the external temperature that's why you'll see lizards and snakes and alligators basking in the Sun or moving slowly when the temperature is cold there are some big advantages to this strategy they require a lot less food to power their metabolisms and they can basically shut down their bodies when it's cold and survive for long periods without sustenance many species even have bouts of daily torpor which is a little like hibernation but lasts for much shorter periods and doesn't disrupt the body quite so much warm-blooded mammals on the other hand are endotherms who generate their own body heat through metabolic processes this means we can get up and go no matter the temperature but we also have to eat a lot more and we have a harder time surviving cold weather and long stretches without food so how did our ancient ancestors evolve from being ectotherms into endotherms it's a transition that would have taken a huge increase in metabolism and doesn't seem likely to have happened all at once researchers now think there would have been an intermediate step something like the listrosaurus that was an endotherm but could still change its body temperature during periods of cold weather or food scarcity in other words hibernation could be a holdover from the days of being ectotherms a reptilian Remnant from the past that many creatures still use today and today reptiles are still some of the most interesting examples of hibernators using extreme techniques to allow them to survive in situations where any other animal would certainly die some of the best hibernators among the ectotherms are freshwater turtles like the painted turtle and the Snapping Turtle though technically their winter torpor is known as brumation because these reptiles live at Northern latitudes where Winter can include freezing temperatures they've had to come up with some incredible adaptations to make it through the cold season when the weather starts getting icy both species will head for shelter at the bottom of lakes and ponds once there they decrease their metabolisms significantly and begin absorbing whatever oxygen is left in the water through a process known as cloacal respiration AKA butt breathing the cloaca is an orifice used for waste removal and laying eggs and adjacent to it are sac-like areas that are filled with blood vessels when the turtles push water into these sacs the papillae absorb the oxygen almost like gills in some species of turtle this type of breathing can account for more than 50 percent of the oxygen they get while swimming but if the winter lasts long enough and the body of water remains covered in ice for a long time eventually the oxygen in the water will run out which means not even butt breathing will allow the turtles to get any air this is when snapping turtles and painted turtles depress their metabolisms even further with their heart beating only once every 5 to 10 minutes this is slow and their cells are barely getting enough oxygen to create energy in the form of ATP but then they do something remarkable they switch to anaerobic respiration this means that their metabolism is using glucose for energy without requiring oxygen we can do anaerobic respiration but by no means can it power our whole body to Keep Us Alive it's far less efficient than aerobic respiration in part because it leads to a massive buildup of lactic acid in the blood this could kill the turtles if not for a handy trick that comes from having shells the turtles are able to pull calcium and magnesium carbonates from their shells to neutralize the lactic acid protecting themselves from harm thanks to the combination of all these abilities painted turtles and snapping turtles are almost always perfectly fine after a long winter although they can still freeze to death if their bodies are covered in ice for too long with butt breathing and an ectothermic metabolism these turtles have winter all figured out but how do mammals survive similarly harsh conditions sure they don't need to butt breathe but they still need to eat to keep their bodies warm right how can such an energy demanding creature simply shut down for months at a time unlike reptiles warm-blooded mammals generally need lots of food to fuel their metabolism especially big mammals like bears brown bears need to eat about 5 000 calories a day so how can they survive a winter without eating one part of this is simple when they're preparing for winter hibernation their calorie intake jumps to about 20 000 calories a day this helps them gain enough weight to survive The Long Winter ahead then once the bear enters their winter Den they go for as long as a hundred days without eating drinking exercising urinating or defecating but unlike other hibernators their internal temperature only drops about 5 degrees Celsius and they still occasionally move around scientists have argued over whether bears are true hibernators because this looks so different than what's seen in smaller mammals but a bear's heart rate Slows To only four beats per minute and their oxygen consumption drops by 75 percent so they're clearly still slowing their metabolism down in a way that looks just like hibernation it seems that the problem with reducing their body temperature so drastically would be in warming themselves back up there's such large animals that the energetic cost is much higher than for bats or squirrels that said they still have some wild tricks for surviving The Long Winter while humans experience bone thinning and muscle wasting with prolonged periods of bed rest bears are able to shut down the genes involved with the breakdown of bone while in hibernation this means they emerge from hibernation weighing a lot less than when they started but most of that weight is fat not muscle and bone on the other end of the spectrum from bears are the Arctic ground squirrels since they live in Canada Alaska and Siberia they spend about seven months of the year in nests buried below the tundra their body temperature falls to the lowest level ever measured in any mammal as low as negative 2.9 degrees Celsius and when their plasma was sampled during this frigid temperature researchers found it had remained liquid despite not having any anti-freeze chemicals in it how is it possible for their very liquid blood to not freeze at these below freezing temperatures scientists have hypothesized that they use supercooling a process in which water goes below freezing temperatures without forming ice because there are no impurities to start the crystallization process but the squirrels don't stay in deep hibernation for the entire winter they go through inter-bought arousals every two to three weeks shivering their body temperature back up to 36.4 degrees Celsius which lasts for about 12 hours hibernating mammals expend about 70 percent of their energy stores for these brief periods of arousal which help them regulate normal body functions like Bears Arctic ground squirrels come out of hibernation without any muscle wasting or brain damage which has led scientists to wonder could we harness some of the same tricks and apply them to humans for those of us who don't love freezing during the winter months hibernation might sound like an ideal way to get through the cold weather but the possibilities for human hibernation go far beyond comfort and convenience imagine what might be possible with long distance space travel if Rockets didn't have to be equipped with so much food and water for astronauts because they'd be in hibernation for most of the voyage it could help them avoid interpersonal conflicts and the mental strain of being in a tiny metal box for months at a time and it might even have health benefits too researchers found that rats placed in a medically induced torpor experienced less harm from radiation which could be a promising development for humans and if we could avoid brain damage as well as muscle and bone loss like other hibernating mammals that would be a huge development for astronauts who already deal with some of those problems on relatively short space missions while this concept might sound like something out of Science Fiction it's already being adapted in more limited ways for medical purposes by cooling the body and the blood of patients doctors are able to perform more extreme heart surgery without killing the individual this therapeutic hypothermia can protect the brain from damage caused by reduced oxygen and allows patients to make a faster recovery and there are even some examples of people who have survived prolonged freezing such as a hiker who was found after 24 days of exposure and whose body temperature had dropped to 22 degrees Celsius or 77 degrees Fahrenheit his body had entered a state of torpor and after being found he was able to make a full recovery and just as it is for bears and Arctic ground squirrels the keys to hibernation May lie hidden in our genome if hibernation is a Remnant from our ancient mammalian ancestors most experts agree that it's an ability that most mammals have simply lost over time the genetic underpinnings may still very much be in our DNA by sequencing and understanding the genomes of today's hibernators scientists are getting closer to understanding how they activate the groups of genes needed for hibernation this all offers a tantalizing possibility not only that we may be able to travel further into the solar system but also that we could extend our lives and survive Strokes heart attacks and severe injuries if little primates like dwarf lemurs can do it and enormous mammals like Bears can do it who's to say that it will never be possible for humans maybe one day we'll be able to pass the winter away from the quiet peacefulness of our own hibernation pods but we can only begin to guess at what comes next for our species if we understand our evolutionary Journey what our future holds is shaped by our past a past so bizarre that it caused humans to become basically the weirdest animals to ever walk the earth we're the only creatures to walk on two legs besides kangaroos sort of the only primate to lose basically all of its fur the only animal to throw but to speak to write down its language where an animal that became so smart with brain so giant that we basically shouldn't be able to exist and yet here we are why did we get so weird how did we diverge so drastically from the other primates why did Evolution Select us to become emotional walking monkeys equipped with a supercomputer for a brain the complexity of human evolution blows my mind and is the subject of our new series becoming human available exclusively on nebula this is our most ambitious project yet and we wouldn't have been able to do it without nebula nebula is a streaming platform that was created by us by the educational YouTube content creators who are tired of worrying about if their ideas would suit the YouTube algorithm's desires sometimes the content we want to make is experimental too long too short or contains themes that would get it demonetized instantly on YouTube sometimes we want to make content that doesn't exactly fit 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Channel: Real Science

Views: 407,592

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Id: 8WaIycNrQMs

Length: 18min 4sec (1084 seconds)

Published: Sat Feb 18 2023

Reddit Comments

[u/Aurelius_Red]

There's only one way to find out.

<climbs into bed>

[u/constant_mass]

What’s the point?