This post was inspired by a conversation with someone, you know who you are – thank you!
I’ve written before about how plants and animals survive the conditions that winter brings, with one well known strategy being hibernation.
A brief period of suspended animation – generally less than a day – is called torpor and researchers are finding that often, what we think of as hibernation, is not the winter long deep sleep that we thought of it as. Instead, hibernation appears to often be made up of a string of periods of torpor, interspersed with periods of non-torpor which seem to be used to sleep. Brain waves have been monitored to find this out and suggests that the periods of torpor are actually periods of sleep deprivation.
During torpor, the animal’s metabolism slows down, their body temperature falls significantly, their breathing rate plummets and so does their heart rate. In bats, for example, the latter can fall from 400 beats per minute down to 11!
But what about humans? Can we hibernate? I know I’d love to…
Before we get into the physiological side of things, let’s consider why humans don’t hibernate. Firstly, our ancestors evolved in tropical climates and so didn’t need to adapt to deal with cold winters and a seasonal dearth of food. Secondly, when we did migrate to colder climates, we developed alternative methods of survival – buildings, fire, clothes, hunting and farming.
Moving on to the biological side of things… A key reason why we can’t hibernate all winter is that our hearts don’t work if they get too cold; they will stop if body temperature falls below 28 degrees Celsius. Clearly this is unhelpful when reduction in body temperature is an important characteristic of hibernation – some animals can survive with a body temperature of just 1 degree…
Whilst some people cite our size as a reason we can’t hibernate:
“The fact that large mammals such as bears and even primates, such as the fat-tailed dwarf lemur of Madagascar, can hibernate means that theoretically humans aren’t too big or energy-hungry to enter torpor. Nor does our evolutionary origin prevent us from doing so, as hibernating animals have been found widely across all types of mammal.”
– Vladyslav Vyazovskiy
However, most hibernating creatures are small – weighing on average 70g – and the exceptions to this, such as bears, don’t tend to hibernate as deeply and their body temperature doesn’t fall as significantly.
In the run up to hibernation, animals must eat a significant amount and in humans this would result in thickening of the artery walls and would lead to heart disease. Further, spending more than a week in bed means that human muscles begin to atrophy and blood clots start to form, putting us at risk of other kinds of awful things such as strokes.
And of course there is the issue of waste. In animals that hibernate, urination and defecation are essentially halted, sometimes through re-absorption which allows for maximum use of nutrients. Humans cannot do this…
Finally, I want to offer just one more reason why we are not physiologically adapted to hibernate. Those animals that do hibernate, remove white blood cells from their blood for the hibernating period, storing them in lymph nodes. This leaves them incredibly vulnerable to immune attacks but it does means that when the body begins to warm up, they will not experience general inflammation. Humans cannot do this and so the warming up period would put us at risk of kidney damage amongst other things.
So, things aren’t looking good for human hibernation… Having said that, research is being carried out into torpor states, primarily for use in medical situations as well as in space travel.
But what about claims that people have hibernated… Firstly, based on the evidence above, it seems unlikely that they have truly, scientifically hibernated. Secondly, we may not actually want to hibernate, given that it actually causes sleep deprivation and many more serious issues.
“There are no known cases of natural human hibernation, according to [Kelly] Drew. But she has heard anecdotes about hibernation-like experiences in her research, including the practice of “lotska,” in which Russian peasants a century ago would supposedly endure the harsh winter by awaking only once per day for 6 months to consume a small amount of bread and ale.”
– Ben Panko
A key reference to the Russian peasants hibernating comes from the British Medical Journal in 1900:
“At the first fall of snow the whole family gathers round the stove, lies down, ceases to wrestle with the problems of human existence, and quietly goes to sleep. Once a day every one wakes up to eat a piece of hard bread, of which an amount sufficient to last six months has providently been baked in the previous autumn. When the bread has been washed down with a draught of water, everyone goes to sleep again. The members of the family take it in turn to watch and keep the fire alight. After six months of this reposeful existence the family wakes up, shakes itself, goes out to see if the grass is growing, and by-and-by sets to work at summer tasks.”
This was said to be a response to conditions which were tantamount to chronic famine and, not having the resources to survive the year, they would use a hibernation like approach in order to eek those resources out.
An episode of QI referenced a group of French peasants who would engage in a hibernation type sleep over winter but all my research into the topic brings me back to the same author. I’m not disputing the factualness of this, but I did want to mention it as this is how urban myths get spread across the internet – one person says something and it gets repeated and repeated without any corroborating evidence.
“Economists and bureaucrats who ventured out into the countryside after the Revolution were horrified to find that the workforce disappeared between fall and spring. The fields were deserted from Flanders to Provence. Villages and even small towns were silent, with barely a column of smoke to reveal a human presence. As soon as the weather turned cold, people all over France shut themselves away and practised the forgotten art of doing nothing at all for months on end.”
– Graham Robb, The Discovery of France: A Historical Geography from the Revolution to the First World War
As much as the idea of hibernation sounds appealing, I’m now thinking I just need to schedule in some duvet days to get through the dark nights and the cold days…