IS THE gloomy weather wearing you down? Does every cheesy, Christmassy jingle send your festive spirit plummeting? Is that health kick abandoned in favour of comfort food and a meaningful relationship with your duvet? Don鈥檛 worry-you鈥檙e in good company. It鈥檚 winter. Perhaps your body鈥檚 trying to hibernate.
Some people get the winter blues on a monumental scale. Sufferers of seasonal affective disorder would rather cosy up to a television set than another human being. They shun sex for some quality time with a pizza, snooze for maybe 16 hours a day, and are often irritable and moody-the holiday atmosphere just passes them by.
Small wonder that SAD sufferers compare their condition to hibernation. When animals prepare to overwinter, they slow their metabolism, retract their gonads, and hunker down in cosy dens, surviving till spring on a comforting layer of fat. The theory that seasonal depression is an atavistic form of hibernation has been doing the rounds for years. Most hibernation researchers and psychologists agreed it was rubbish. But recent research has reawakened interest in the theory.
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It鈥檚 true there are big differences between seasonal blues and other forms of depression. Clinically depressed people usually lose interest in food, finding it tasteless or even unpleasant. They often shed weight and have great trouble sleeping. Sufferers of seasonal depression are just the opposite, eating and sleeping with gusto. While SAD affects just a few per cent of the population, many researchers believe that most of us are susceptible to seasonal overeating, oversleeping, and a general bodily go-slow. Some even say it鈥檚 the extreme end of a spectrum of adaptive responses to winter weather. 鈥淲e want to establish whether SAD is part of our genetic background,鈥� says George Wilson of the University of Tasmania in Hobart. 鈥淚t could be a programmed reaction to shorter daylight hours in winter.鈥�
Two recent studies have uncovered hibernation-like physiology in people with SAD. Margaret Austen, one of Wilson鈥檚 colleagues in Hobart, where winter nights average 15 hours long, looked at SAD-related changes in the autonomic nervous system. These nerves regulate the functions we don鈥檛 think about, like breathing and heart rate, and are deeply involved in hibernation. And it turns out that they could be just as prominent in seasonal depression.
There are two parts to the autonomic nervous system, which work in opposition to control bodily functions. The 鈥渟ympathetic鈥� system boosts metabolism, while the 鈥減arasympathetic鈥� system damps down bodily functions. Just before animals hibernate, they experience a spike in the activity of their parasympathetic nervous system, which slows their heart rate and decreases their body temperature and metabolic rate.
Austen found a similar parasympathetic response in people with SAD. As a result, her patients had slower heart rates and low energy levels. 鈥淎nimals prepare for winter by fattening up and then sleeping through it,鈥� says Austen. 鈥淚n humans that is not practical, so instead we eat more and gain weight through the winter, and we lack energy and sleep more.鈥�
Another study by Arcady Putilov, a researcher at the Russian Academy of Sciences in Novosibirsk, Siberia, also found hibernation-like activity in his SAD patients. They consumed less oxygen and had lower resting metabolic rates than people who weren鈥檛 depressed-very similar to the slowed physiology of hibernating animals during the winter.
Putilov says there is no doubt that the symptoms of SAD are our way of coping with winter. The binge eating, the fat deposits that form on your thighs, the feeling you could sleep for 24 hours-all are signs of an adaptive mechanism aimed at conservation of energy.
A fizzling winter sex drive is an adaptation to the winter chill too, says Thomas Wehr of the National Institute of Mental Health near Washington DC. Historical and experimental evidence shows that human responses to seasonal changes may have been more pronounced before electric lighting was common. Low sex drive in winter could have served both to conserve energy through the winter and ensure that your offspring are born at a time when food is available. Babies conceived in winter would be born in autumn, when food is starting to become scarce. Babies conceived in summer would be born in spring, when food is starting to be plentiful. 鈥淭here are definite parallels between SAD and seasonal influences on human reproduction,鈥� says Wehr.
An exploration of the genes involved in hibernation indicates that humans certainly possess all the necessary machinery to hibernate. Matthew Andrews at the University of Minnesota at Duluth discovered two genes responsible for shifting metabolism to burn fats from reserves rather than carbohydrates, a vital process for kick-starting hibernation. A host of other genes are involved too. 鈥淎lmost every gene we鈥檝e looked at so far [in animals] is found in humans,鈥� says Andrews. It seems that these genes are common in mammals but that hibernators have found particular ways of harnessing them to ensure their survival under extreme conditions.
Although each animal follows slightly different cues that tell when it is time to hibernate, day length is always a key factor. The shortening period of light tells the body鈥檚 circadian clock that winter is approaching. Even ground squirrels, which seem to have an inbuilt annual clock and go into hibernation regardless of day length, use it as a way calibrating their annual timekeeper. Shorter days also trigger SAD. Treatment of SAD usually includes sessions in front of a strong light source each morning. This phototherapy works by tricking the circadian pacemaker in the brain, and it works well at improving mood and reducing lethargy and food cravings.
But do these many hibernation-like adaptations mean our ancestors actually hibernated? Is SAD an evolutionary leftover? Andrews says that the existence of the genes alone is no proof that humans once hibernated. Still, he says, 鈥淚f there were any vestige of hibernation in humans, it makes sense that it would be something like SAD.鈥�
But if humans had hibernating ancestors, shouldn鈥檛 we all get SAD in the winter? Wehr believes that all humans have the potential to succumb to seasonal affects, but that most of us can ignore changes in day length because we live in a world of artificial lights. People with SAD don鈥檛 seem to be able to use artificial light to set their circadian pacemaker, according to recent work by Wehr. 鈥淚 suspect what we call winter depression has its origins in evolutionary biology,鈥� he says. 鈥淭he symptoms of winter depression might well have been normal behaviour but now we view them as extreme.鈥�
Despite the many biological similarities between hibernation and seasonality in humans, many researchers are far from convinced. Hibernators gorge themselves before they retreat into their dens, not during winter as we do. Hibernating squirrels can drop their body temperatures to just above freezing for weeks at a time, something we couldn鈥檛 dream of. Even bears, much closer to us in size, are capable of surviving up to five months on their own body fat, something few of us could muster.
But lots of non-hibernating animals make it through winter in a somnolent torpor, reducing their body temperatures and whittling their metabolisms down to a minimum. Madagascan lemurs retire to a tree-hole during the winter, where they sit like zombies for days on end. It鈥檚 lack of food, rather than cold, that drives the lemurs to hibernate. Since humans evolved in the equatorial climes of Africa, perhaps our hunter-gatherer ancestors may have evolved a similar ability to survive long periods without food.
Nowadays we just have to survive long nights. Luckily we can load up on holiday sweets and spirits to help us make it through the winter. Crawl under the covers, get the candles lit and the fire roaring, hit the remote control, and let those holiday party invitations pile up. Don鈥檛 feel guilty. After all, you are just doing what comes naturally.
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Let there be light
THAT we are creatures of light is never more obvious than at Christmas. The first people to colonise the inhospitable north got through the long winter nights by inventing festivals of light and of fire. Bonfires, torch-lit processions, roaring hearths and burning candles all lightened the gloom of midwinter.
So it鈥檚 not by accident that our biggest national festival comes slap bang in the middle of the northern winter. For millennia, it has been the perfect occasion to brighten and warm away the seasonal gloom with one helluva party-ever since humans first made it to the temperate zones, anyway.
The timing of the Christian festival of Christmas gives the game away. The shortest day of the year, the winter solstice, falls tellingly close, on 21 December. In the old days, anyone keeping an eye on the solar calendar must have thought-hallelujah, lighter days are on the way, homebrew all round!
Besides the booze, bonfires were the Big Event for midwinter鈥檚 day from prehistoric times, according to the pioneering folklorist James George Frazer, who in the 1920s penned a two-volume study of ancient fire festivals. Apparently, bones were tossed into the flames to create foul odours that would ward off evil spirits. The word 鈥渂onfire鈥� comes from bone fire. Nowadays we have office parties instead.
When Christianity took hold, traces of these ancient practices lived on. In Britain, the 11th-century Danish rule over England introduced the colloquial Scandinavian term for Christmas, 鈥淵ule鈥�. In medieval times, the Yule log-the largest possible that could be communally dragged into the hearth-was ceremoniously lit on Christmas Eve. Today, the mighty Yule log is remembered by the chocolate Swiss roll cake. It seems to have lost something in the translation.
All the same, today鈥檚 urbanites still yearn for light, greenery, warmth and joy in midwinter, says Ronald Hutton, professor of history at the University of Bristol and a leading scholar of modern festivals. We will happily flash our credit cards to procure the means to create domestic versions of our ancestors鈥� unruly bonfires. Functional fireplaces and wood-burning stoves are fashion statements these days.
Even the humble candle is big business. John Terrell Fry of Little Rock, Arkansas, the author of The Candlelit Home, now works as a 鈥渃andle consultant鈥� all over the world. Meanwhile, in Sydney, Australia, Amanda Hammond, author of Illuminate Living with Candles, reminds us that these small incendiary devices may no longer be a practical necessity but remain a 鈥減owerful symbol of inner enlightenment鈥�.
The electric light bulb, invented in 1879, soon drove candles to near extinction. But as the 20th century drew to a close, candles miraculously revived, undergoing what Hammond calls an 鈥渦nprecedented renaissance鈥�. Today, she opines, candles are widely appreciated as 鈥渁 symbol of relaxation, celebration, romance and ceremony鈥�.
Such talk is calculated to irritate fire ecologist Stephen Pyne of Arizona State University. This is 鈥渟heer symbolism鈥�, he says. Our dependence on fire has become hidden in machines and delivered along electricity wires. In Europe, burning candles once bedecked Christmas trees-to furnish light, it was said, for the woodland spirits sheltering in evergreens after deciduous trees have lost their leaves. But the elves and pixies were in for a shock. Electric tree lights first appeared in 1882 in New York, only three years after Edison鈥檚 invention of the light bulb. By the 1930s, electric fairy lights-with the bulbs hand-blown in Germany in the shape of snowmen, Santas and fairies-were the norm. Now you can buy fibre-optic Chinese-made Christmas lights, or 鈥渕ulti-function鈥� tree lights that operate in eight modes: 鈥渃ombination, in waves, sequential, slo-glo, chasing/flash, slow fade, twinkle/flash and steady on鈥�.
It鈥檚 tempting to mock our enthusiasm for such decorations, but might some ancient spirit of midwinter celebration endure all the same? Reassuringly, Hutton thinks it does. 鈥淲hen all is said, a vigorous seasonal festive culture survives and continues to develop among the British,鈥� he argues.
Yet what鈥檚 most noticeable about our celebrations these days is their privatisation, says Hutton. A century or two ago, the great annual celebrations revolved round community groupings-the clan, say, or the great household, the manor, the parish and the church. But today鈥檚 festivals centre on the family or the couple, and are typically celebrated at home or at private parties.
We still do notice changing day lengths, but that natural fact no longer acts as the prime signal for communal celebration. Our lives revolve around our closest associates-our families, lovers, friends and workmates. 鈥淗umanity has come to replace the natural world at the centre of the wheel of the year,鈥� says Hutton. This state of affairs has its advantages: now we can party whatever the season. All the same, we still find ourselves staring at the light from open fires and naked flames-in recognition, perhaps, of what we have lost.
Fire rites evolved out of fire鈥檚 practical biology, Pyne says-its capacity both 鈥渢o purge and to promote鈥� in the living landscape. But in the industrial city of the 21st century, fire rites have shrunk to votive candles and eternal flames over memorials. 鈥淲hat has been lost is the daily interplay between people and flame,鈥� he laments. For as we鈥檝e hidden fire鈥檚 ecology in machines, we鈥檝e gradually lost the knowledge that our livelihoods ultimately depend on the energy of combustion. Once, he argues, humans knew that what made our species unique was our ability to control fire. Now, we risk the very future of the world鈥檚 biosphere in a profligate orgy of hidden fire. And to think it all started with those blasted prehistoric bonfires-happy Christmas, everyone!