George Orwell was right: all men are equal but some are more equal than others. This is most apparent on cold, dark, winter mornings, when barometers read below zero, hailstones threaten to crack the windows and the early morning larks come into their own.
They're the ones who somersault out of bed, do 10 quick press-ups, then cartwheel across the floor in the direction of the shower.
Meanwhile, the night owls lie motionless, save for the occasional REM-induced flickering of an eyelid, despite the incessant clanging of saucepan lids by a clatter of pyjama-wearing kids, eager to be fed.
By definition, larks wake up to two hours earlier than the rest of the population and are ready for bed between 8pm and 10pm. Owls, on the other hand, naturally wake two hours later than most, and typically become sleepy between midnight and 2am.
If you linger over morning coffee, exercise early, and are at your most alert around noon, then you're probably a lark. If napping is something you rarely do, breakfast is your favourite meal and an alarm clock is not something you need, then you probably are.
Night owls, on the other hand, rise with the aid of multiple alarms, feel sleepy when they wake and nap regularly.
They also exercise in the evenings, stay up later at weekends and on holidays, favour dinner to breakfast and are at their most productive both late morning and late evening.
As to whether you're a lark or an owl, the answer is probably neither, as research carried out at the University of Carolina shows that the two types account for only 30pc to 40pc of the population, with the rest having no real propensity for mornings or evenings.
Interestingly, it also shows that owls outnumber larks by two to one.
The reason why some people are larks and others owls is genetic. Scientists from the Sleep Laboratory at the University of Surrey discovered that the body-clock gene, Period 3, which determines whether we are larks or owls, also controls how we are affected by sleep deprivation. Apparently, there are two types of the gene, a longer and a shorter, and those with the former need more sleep.
Once scientific evidence rubbished the notion that the morning sluggishness typical of night owls originated in laziness, it was inevitable that someone, someday, would speak out on their behalf.
That someone was Camilla Kring, founder of Denmark's B-Society, a 5,000-member pressure group for night owls, which calls for "an uprising against the tyranny of early rising."
"We want to create a flexible society, one which accommodates B-people -- those who are genetically predisposed to wake and work later," she says.
Her ideas are catching on in Denmark, but there's no doubt that here, we live in a culture which doesn't give a whit when we are at our peak. And as the global economy demands more productivity to fuel a 24-hour society, workers are being called upon to labour through the night.
David Dinges, a biological psychologist from the University of Pennsylvania, believes that sleepy workers account for between 60pc and 90pc of industrial mishaps.
In support, he quotes the nuclear accidents at Chern-obyl and Three Mile Island, the chemical disaster at Bhopal and the Exxon oil spill, all of which occurred during graveyard shifts.
Of course, most of us work out of financial necessity, and some of the best-paid shifts don't suit our sleep rhythms.
For those whose jobs take them behind the wheel when they're exhausted, the consequences can be dire -- especially when we consider that driver fatigue is thought to be a factor in up to 20pc of fatal accidents in Ireland.
Naps for night-shift workers could be a good idea. A study for the National Aeronautics and Space Administration, showed that pilots who took 40-minute sleep-breaks during flights were more alert than those who didn't.
The idea makes perfect sense, but until it catches on here, it's best to avoid being caught napping by your employer. Unless, of course, you're planning a more permanent break from the workforce.
The night owl...
Sheila O'Flanagan is a best-selling author. Her latest novel, Bad Behaviour, is published by Headline Review and is in all good bookstores now.
"Writing late into the night suits me well, as it's quiet and there are no distractions, such as phone calls or requests to do other things.
"But while those are practical incentives, the main reason I work best at night is that I get a great burst of energy at around 7pm and another four hours later. Often, I write until 3am in the morning, and while I could go on after that, I usually call a halt.
"Most mornings, I'm up between 8am and 9am at the latest, but I'm cranky and don't talk much until I've had my coffee. Even then, I'm not at my best before 10am. For breakfast, I have fruit and yoghurt, but it's a meal which holds no appeal for me, and I didn't bother with it for years.
"I grew up with two sisters who were also night owls, so mornings were comfortable with the three of us ignoring one other at the breakfast table.
"Our mother is a lark and, while she probably hoped that we'd chat to her over breakfast, we didn't. Funnily enough, she's beginning to show more and more owl-like tendencies as the years go by."