The Insane Evolution of: Hibernation

The forests of Madagascar are filled with some of the most unusual species in the world. Chameleons crawl between trees and over strange volcanic formations. The carnivorous fossa hunts rodents, birds and ring-tailed lemurs, and perhaps the strangest of all are the fat-tailed flamingos with long tails and enormous eyes, these nocturnal primates only weigh about 160 grams and feed on fruits, insects and small animals, but that's only for half the year; During the other six or seven months, during the forest's dry season, these lemurs hibernate in tree holes and feed on fat reserves in their tail. Their body temperature can fluctuate up to 20 degrees Celsius as the temperature outside From their nests their heart rate rises and falls, their breathing rate and their brain activity levels also fall precipitously and, although

hibernation

is in no way the same as sleep.

In reality,

hibernation

can lead to lack of sleep. These little lemurs seem pretty dead to the world. In fact, scientists recently discovered that two other species of dwarf lemurs that live in the high-altitude forests of eastern Madagascar hibernate in underground holes, protecting themselves from near-freezing temperatures. When scientists discovered their burrows, they found very soft hairballs. Curled up, lemurs in full hibernation, these miniature lemurs are the only known species of primate that hibernates, but this seasonal shift toward a decreased metabolism and reduced body temperature is widespread throughout the animal kingdom in which we see it. freshwater turtles, ground squirrels, bats and of course bears, it is an essential adaptation that allows species to survive frigid winters and reduced food availability, not only that, but hibernating species actually have a hope longer-lived than species of similar sizes that do not hibernate, as humanity has known.

The ability of animals to hibernate for thousands of years dates 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. time and some species of turtles go more than 100 days without breathing, how do these animals achieve such remarkable feats? Where did hibernation come from in its

evolution

ary history? Could humans one day achieve the same? The history of hibernation begins hundreds of millions of years ago. When all of Earth's landmasses were grouped into a supercontinent called Pangea, during this time a strange animal roamed the region that would become Antarctica and extend to what is now India and southern Africa.

The listrosaurus was a four-legged forager with fangs in its upper jaw. It usually grew to the size of a pig, but sometimes reached eight feet 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 periods without sunlight each year, when researchers compared listrosaurus fossils found in Antarctica with those found further afield. To the north, they made a surprising discovery: growth patterns in the tusks of those who lived around the Antarctic Circle showed annual stress marks that are very similar to those we see in modern animals that go into hibernation.

Those researchers hypothesized that this could be evidence of hibernation in some of our earliest mammalian ancestors. The ability to hibernate seems strongly related to the way reptiles manage their body temperature and metabolism, which is completely different from how mammals do it. At Popular Science we think of reptiles as cold-blooded, but the technical term for them is Ectotherms, this means they cannot produce their own body heat and instead rely on the external temperature, which is why you will see lizards and snakes and alligators basking in the sun or moving slowly when the temperature is cold. This strategy has big advantages: they require much less food to fuel their metabolism and can basically shut down their bodies when it gets cold and survive for long periods without many species even having bouts of daily torpor, which is a bit like hibernation, but lasts for periods. much shorter and does not alter the body as much.

Warm-blooded mammals, on the other hand, are endotherms that 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 find it harder to survive cold weather and long periods without food. So how did our ancient ancestors evolve from ectotherms to endotherms? It's a transition. That would have required a huge increase in metabolism and it doesn't seem likely that it would have happened all at once. Researchers now think there would have been an intermediate step, something like listrosaurus, which was an endotherm but could still change its body temperature during cold periods. weather or food scarcity, in other words, hibernation could be a holdover from the days when they were ectotherms, a reptilian remnant of the past that many creatures still use today and reptiles remain some of the most interesting examples of hibernators. who use extreme techniques to allow them to survive in situations where any other animal would certainly die.

Some of the best hibernators among ectotherms are freshwater turtles such as the painted turtle and snapping turtle, although technically their winter torpor is known as brumation because these reptiles live in northern latitudes where winter can include frost. temperatures, they have had to make some incredible adaptations to survive the cold season, when the weather starts to turn icy. Both species will take refuge at the bottom of lakes and ponds. Once there, they will significantly slow their metabolism and begin to absorb any oxygen. It is left in the water through a process known as cloacal respiration, also known as butt respiration, the cloaca is an opening used to remove waste and lay eggs and adjacent to it are sac-like areas that fill with blood vessels when turtles push water into these sacs.

The papillae absorb oxygen almost like gills in some species of turtles. This type of breathing can account for more than 50 percent of the oxygen they get from swimming, but if winter lasts long enough and the body of water remains covered in ice for a long time time. Over time, the oxygen in the water will run out, meaning that even full breathing won't allow the turtles to get air. This is when snapping turtles and painted turtles further depress their metabolism and their heart beats only once every 5 to 10 minutes. slow and your cells barely get enough oxygen to create energy in the form of ATP, but then they do something remarkable: they switch to anaerobic respiration, this means that your metabolism uses glucose for energy without requiring oxygen.

We can do anaerobic respiration, but not in any way. Can it power our entire body to keep us alive? It is much less efficient than aerobic respiration, partly because it leads to a massive buildup of lactic acid in the blood. This could kill the turtles if it weren't for a useful trick that comes with having shells on turtles. They are able to extract calcium and magnesium carbonates from their shells to neutralize lactic acid, protecting themselves from any 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 anal breathing and an ectothermic metabolism.

These turtles have discovered winter, but how do mammals survive in equally harsh conditions? I'm sure they don't need to breathe but they still need to eat to maintain their bodies. How can such an energy-demanding creature simply sit still for months at a time, unlike reptiles? Warm-blooded mammals generally need a lot of food to fuel their metabolism, especially large mammals like bears. Brown bears need to eat about 5,000 calories a day. Then how? Can they survive a winter without food? Part of this is simple. When they prepare for hibernation, their calorie intake increases to approximately 20,000 calories per day.

This helps them gain enough weight to survive the long winter ahead and once the bear enters your home. In the winter, they go up to one hundred days without eating, drinking, exercising, urinating or defecating, but unlike other hibernating bears, their internal temperature only drops by about 5 degrees Celsius and they still move occasionally. Scientists have argued over whether bears are true hibernators because it appears that way. Unlike what's seen in smaller mammals, but a bear's heart rate slows to just four beats per minute and their oxygen consumption drops by 75 percent, so they're clearly still slowing their metabolism down a notch. way that looks like hibernation, it seems that the problem reducing their body temperature so drastically would be to warm up again, there are animals so large that the energy cost is much greater than that of bats or squirrels, which said they still have some wild tricks to survive the long winter, while humans experience thinning of bones and muscles.

Bears with prolonged periods of bed rest can turn off genes involved in bone breakdown while in hibernation, this means they emerge from hibernation weighing much less than when they started, but most of that weight is fat, not fat. muscles or bones. The other end of the bear spectrum are Arctic ground squirrels, as they live in Canada, Alaska and Siberia. They spend about seven months of the year in nests buried beneath the tundra. Their body temperature drops to the lowest level ever measured in any mammal. as negative 2.9 degrees Celsius and when samples of his plasma were taken during this frigid temperature, researchers discovered that it had remained liquid despite not having any antifreeze chemicals, how is it possible that his very liquid blood does not freeze at these temperatures below zero?

It was hypothesized that they use supercooling, a process in which water drops below freezing temperatures without forming ice because there are no impurities to start the crystallization process, but the squirrels do not remain in deep hibernation all winter. ; They go through wake-ups between purchases every two. to three weeks by bringing your body temperature back up to 36.4 degrees Celsius, which lasts about 12 hours. Hibernating mammals expend about 70 percent of their energy reserves in these brief periods of arousal that help them regulate normal body functions, like bears. Arctic ground squirrels emerge from hibernation without muscle wasting or brain damage, leading scientists to wonder if we could harness some of the same tricks and apply them to humans.

For those of us who don't like freezing during the winter months, hibernation might seem like an ideal way to achieve this. through cold weather, but the possibilities for human hibernation go far beyond comfort and convenience. Imagine what could 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 would be in hibernation. for most of the trip could help them avoid interpersonal conflicts and the mental strain of being in a small metal box for months and could even have health benefits. The researchers found that rats placed in medically induced torpor experienced less radiation damage, 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, It would be a huge advance for astronauts who already face some of those problems on relatively short space missions, while this concept may seem like something out of science fiction.

It is already being adapted in a more limited way for medical purposes by cooling the body and blood of patients. Doctors can perform more extreme heart surgeries without killing the individual. This therapeutic hypothermia can protect the brain. damage caused by reduced oxygen and allows patients to recover faster and there are even some examples of people who have survived prolonged frostbite, 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 lethargy and after beingfound was able to fully recover and, as with bears and Arctic ground squirrels, the clues to hibernation may be hidden in our genome if hibernation is a remnant of our ancient mammalian ancestors most experts agree agree that it is an ability that most mammals have simply lost over time the genetic underpinnings may still be in our DNA by sequencing and understanding the genomes of today's hibernators scientists are getting closer to understanding how they activate groups of genes necessary for hibernation, all of this offers a tantalizing possibility not only that we could travel deeper into the solar system but also that we could extend our lives and survive heart attacks and serious injuries if small primates like dwarf lemurs can do so and Huge mammals like bears can do it, who's to say it will never be possible for humans, perhaps one day we will be able to spend the winter away from the tranquility of our own hibernation pods, but we can only begin to guess what is to come.

Next up for our species, if we understand our

evolution

ary journey, what the future holds is shaped by our past, a past so strange that it caused humans to become basically the strangest animals to ever walk the Earth, we are the only creatures that walk on two legs. kangaroos are the only primate that loses basically all of its fur, the only animal that pulls but talks to write its language, where an animal that became so intelligent with such a giant brain that we basically shouldn't be able to exist and yet here Why did we become so weird?

How did we diverge so drastically from other primates? Why did Evolution select us to become walking emotional apes equipped with a supercomputer for a brain? The complexity of human evolution blows my mind and is the subject of our new Becoming Human series available exclusively on Nebula. This is our most ambitious project yet and we couldn't have done it without Nebula. Nebula is a streaming platform created for us by YouTube educational content creators who are tired of worrying whether their ideas would fit the wishes of the YouTube algorithm. Sometimes the content we want to create is experimental, too long, too short, or contains topics that would instantly demonetize it on YouTube.

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