The world is divided into those who will do anything to get their kicks - like hurling themselves out of aeroplanes or scaling skyscrapers face down - and those who will do anything to avoid these situations.
As someone whose idea of an adrenaline sport is driving around Hyde Park Corner at rush hour, I have no understanding of why pot-holing was ever invented or what anyone could possibly hope to accomplish by bungee jumping. But then I belong to the latter and much larger group of people, who psychologists call risk-averse and who children call scaredy-cats.
There's no doubt about it, though, more and more people are drawn - repeatedly - towards the edges of acceptable risk. Just look at the plethora of activity magazines andbooks on the news-stands extolling the death-defying delights of hang-gliding, parachuting, caving, white-water rafting and bridge-swinging. (You don't want to know, but it involves zip wires, pulleys and great heights. ) While Jane Fonda cajoled us into going for the burn by doing aerobics all those years ago, today it's going for the adrenaline rush.
But there's adrenaline and there's adrenaline. We all have the chemical in us. It's just that we respond to it in different ways. As consultant psychiatrist Raj Persaud puts it: "Adrenaline makes you feel aroused, but how you interpret the arousal depends on thecontext you find yourself in - whether, for instance, you're in love or on a roller-coaster. It's unlikely to be a motivating factor in itself."
Adrenaline is one of two naturally occurring hormones released by the adrenal gland when we are under stress, are frightened or when we exercise. It makes your heart beat faster, widens your airways to improve breathing and increases the flow of blood to the muscles, preparing them for fight, flight or just a whopping good work-out.
You don't have to be in extreme physical or emotional situations to know what adrenaline feels like. Teachers know it well: especially the newly-qualified trying to control the quaking in their boots. And it's certainly there in great dollops when the inspectors call.
It also has its positive side. Professor Tim Wheeler of Southampton Institute explains: "In small, short doses adrenaline is a very positive thing. There's an almost theatrical element of performance for teachers - and adrenaline gives that performance an edge. But there's a big difference between the acute adrenaline buzz you get when you're teaching well or giving a good lecture, and the chronic stress that some teachers suffer, which is debilitating."
Many teachers are seeking bigger buzzes. An all-woman expedition to the North Pole last summer included Sarah Jones, a 30-year-old PE teacher from Kent, who braved 20 days of sub-zero degree temperatures, low rations and cramped living conditions to experience the "exhilaration" of pulling it off. One of her fellow trekkers, recruitment consultant Victoria Riches, was so moved by the experience that she decided to jack in her job and do something more worthwhile with her life. She is now training to be a teacher.
Somewhat closer to home, Berkhamsted music teacher Jane Archer, 29, gets her thrills in a different way. For the past 18 months, she has been smitten with gliding. You'd be hard-pressed to find a less likely candidate. "I'm not a very good traveller," she laughs. But despite bouts of persistent air sickness, never mind a couple of unscheduled landings in fields, she hasn't been put off flying gliders. "It's better than any roller-coaster ride - exciting and scary at the same time. It's a great feeling when you're in control of something that's dangerous, something that could go wrong, like when you do aerobatics. You're pushing the glider to its limits."
The attractiveness of danger in a world in which so many dangers have been eradicated is a pull for adrenaline adventurers like Jane. Robbin Eggar, author of GQ Active's guide, Daring Days Out, explains: "The society we live in is so safe. We're so protected. We're not even so frightened of death anymore because we don't see it. It's resulted in the blanding down of our male, baser emotions. We don't get extremes of fear. But most people have a need for extremes, a need to want to test themselves against something, a need for adrenaline rushes."
But is it true that all people have these needs? Not necessarily, says Raj Persaud. First, he points out that men are more predisposed to taking risks than women. Evolutionary biologists would say this fits in with our evolutionary past, when men had to hunt dangerous beasts while women looked after the children; sociologists would say that men and women were socialised into these roles.
Going beyond the gender divide, Dr Persaud refers to Hans Eysenck's theory that humans are either under-aroused or over-aroused. "Thrill seekers," explains Persaud, "are under-aroused and easily bored while those who are over-aroused don't like too much external stimulation. They tend to be introverts and are more easily absorbed in what they're doing." Contrary to stereotype, it has nothing to do with intelligence. It is, in fact, something that we are programmed with.
There are, of course, other explanations. Raj Persaud says Freud would explain the need of some people to expose themselves to anxiety-producing situations as a need to master things, "pushing ourselves to the edge to see if we can cope".
But there is also something a lot more banal about it all. "Just as people don't buy a Rolex for its function but for what it says about them, similarly people try to buy an identity through these pursuits. It goes back to the evolutionary model: the more rugged and risk-taking the man, the better able he is to pass down his genes."
But what about the women? Jacky McPherson is a science teacher from Chichester in her everyday life; an inveterate skydiver and motorcyclist the rest of the time. For her, "it's the ability to use the adrenaline and control it that keeps me doing it". But she also admits that "the real high that you get from a successful jump makes you want to do it again. It's addictive."
She doesn't see herself as a natural born risk-taker, nor does she see sky-diving as a dangerous sport. "If you're careful and sensible, the chance of risk is very low."
Not so, says Tim Wheeler. "All the evidence shows that we're not very good at assessing risk. And when it comes to dangerous sports, we have no accurate information. Most people don't know, for instance, that you are between 19 and 20 times more likely to be killed on a motorbike than in a car. And for hang-gliding, the question is not so much if you have an accident, but when. But for many people involved in adrenaline sports, there is an illusion of control. They believe that the locus of control is theirs and therefore they are safe."
Some of these people, he believes, develop physiological dependencies on adrenaline hits. And to get their highs, they have to climb that much higher than the time before, or try something altogether different as they become habituated to one sport.
But for the most part, people tend to get their adrenaline rushes in a safe context, like going to a fun fair or amusement park or even, if you're a real wimp, driving around Hyde Park Corner during rush hour. Some of us are made for taking more risks than others, that's all.
THE THRILL-SEEKERS' GUIDE TO DANGEROUS PURSUITS
British Hang-Gliding and Paragliding Association The Old Schoolroom Loughborough Road Leicester LE4 5PJ Tel: 0116 261 1322
British Balloon and Airship Club Wellington House Lower Icknield Way Longwick, Nr Princes RisboroughBucks HP27 9RZ Tel: 01604 870025
Personal Watercraft Federation (for jet-skiing) CSL House 184 Histon Road Cambridge CB4 3JP Tel: 01223 516769
British Sub Aqua Club (for diving) Telfords Quay Ellesmere Port South WirralCheshire L65 4FY Tel: 0151 350 6200
British Surfing Association Champions Yard PenzanceCornwall TR18 2TA Tel: 01736 360250
The English White-Water Rafting Committee co Current Trends Adbolton Lane West Bridgford Nottingham NG2 5AS Tel: 0115 981 8844
National Caving Association Monomark House 27 Old Gloucester St London WC1 British Mountaineering Council 177-179 Burton Road Manchester M20 2BB Tel: 0161 445 4747
British Elastic Rope Sports Association (for bungee jumping) 33a Canal StOxford OX2 6BQ Tel: 01865 311179
British Gliding Association Kimberley House Vaughan Way Leicester LE1 4SE Tel: 0116 253 1051
British Parachute Association (for skydiving) 5 Wharf Way Glen ParvaLeicester LE2 9TF Tel:0116 278 5271
Royal Yachting Association (boat racing, wind-surfing, sailing) RYA House Romsey Road Eastleigh Hampshire SO50 9YA Tel:01703 627400