Lv3 Animal B: Hibernation

Onboard（船内での）the spacecraft, the astronauts preset（あらかじめセットしておく）the timer, enclose（閉じ込める）themselves in capsules, and fall into a deep hibernation（冬眠）that'll carry them several hundred years into the future. 

This is a familiar scene in many sci-fi films, but could humans ever actually hibernate（冬眠する）in real life? 

Researchers interested in this question turn to the animal kingdom, where hibernation is commonplace（よくあること）, occurring in over 200 species that we know of. 

Take the Arctic ground squirrel（北極ジリス）. Native（固有の）to the North American tundra（凍土帯） and northern Russia, this animal burrows（穴を掘る）beneath the permafrost（永久凍土帯）and slips into a state of suspended animation（仮死状態）, its body temperature plummeting（急に下落する）to a frigid（厳寒の）-2.9 degrees Celcius. 

Others, like the female black bear, can multitask（複数のタスクを同時に進行する）, giving birth and lactating（乳を出す）while they're hibernating through the winter. The fat-tailed dwarf lemur（フトオコビトキツネザル）prepares for its long dormancy（休止状態）by gorging（むさぼり食う）on food and storing the majority of its fat reserves（備蓄）in its tail, doubling its body weight. After hibernation, it emerges（現れる）looking as svelte（ほっそりとした）as ever. 

So why do these animals go to such extremes? 

Hibernation is a necessity, a survival tactic for making it through the harsh winter months when dwindling（だんだん減少する）food and water reserves threaten（おびやかす） survival. 

For many years, experts believed hibernation happened only in arctic（北極地方の）and temperate（温暖な）environments. But more recently, they've discovered animals hibernating even in arid（乾燥した）deserts and tropical rainforests. 

As hibernation kicks in, animals' heartbeats（心拍）usually slow to about 1 to 3% of their original speed, like the dwarf lemur's, which drops from its usual roughly 180 beats per minute to just around four. 

Breathing also declines dramatically to just one breath every 10 to 21 minutes in the lemur's case. And black bears, like most hibernators, don't urinate（排尿する）or defecate（排便する）the entire hibernation season. Hibernating animals appear to stay alive by having just enough blood and oxygen moving around their bodies.

And scans（精密検査）of hibernating animals reveal that their brain activity has just about flat-lined（死んだ）. But hibernation isn't a long winter's nap. As far as researchers know, in lemurs and ground squirrels anyway, the animals aren't even sleeping for most of it. 

Hibernation is actually made up of regular bouts（一期間）of reduced metabolic（新陳代謝の）rate and body temperature known as torpor（動物の休眠状態）. Animals can be in torpor for a few days to five weeks, after which they resume（再開する）normal metabolic rate and body temperature for about 24 hours, before going back into torpor again. The phenomenon is known as an interbout arousal（中途覚醒）, and why it occurs is still a mystery. 

The behaviors inherent（内在する）in hibernation, like going five weeks without sleep, or dropping to near-freezing body temperatures would be potentially fatal（命に関わる）to non-hibernating species like us. 

To find out how hibernators are able to do this, researchers turned their attention to those animal's genomes（DNAに含まれる遺伝子情報の総体）. So far, they've discovered that hibernation is controlled by genes that turn off and on in unique patterns throughout the year, fine-tuning（微調整する）the hibernator's physiology（生理機能）and behavior. 

For example, ground squirrel, bear and dwarf lemur studies have revealed that these animals are able to turn on the genes that control fat metabolism（新陳代謝）precisely when they need to use their fat stores as fuel to survive long periods of fasting（断食）. 

And the genes in question are present in all mammals, which means that researchers could study hibernating mammals to see how their unique control of physiology might help humans. 

Understanding how hibernators deal with reduced blood flow could lead to better treatments for protecting the brain during a stroke（脳卒中）. Figuring out how these animals avoid muscle deterioration（低下）might improve the lives of bedridden（寝たきりの）patients.

And studying how hibernating animals control their weight with ease（容易さ）could illuminate（解き明かす）the relationship between metabolism and weight gain in humans. And yes, more research in this area might someday make human hibernation a real possibility. 

Imagine our surprise if the key to intergalactic（銀河系間の）travel turns out to be ground squirrels, black bears, and dwarf lemurs.