I am at a sold out 10km run in Central Park, New York. I am not sure what I am doing here as I can barely run for 5 minutes before I run out of breath. But this is a special race—the Boomer’s Cystic Fibrosis Run to Breathe 10K—and among the 5,000-plus participants there are some with the deadly lung disease. My family—they are running too—has talked me into this by pointing out that if people with serious health problems can do it then a relatively healthy woman like me can too. I have trained erratically for a couple of months and the best I have done so far is a walk-run mishmash of 9km. As I stand among the throng of runners—a numbered bib on my T-shirt, a timing chip on my shoe—I worry if I will finish. Then I look around and see the girl beside me getting ready with a puff from an inhaler. There are others with a tube going past their nose. I feel humbled. And inspired.

I am happy to report that I completed the race, a small miracle for me. So many pictures flash through my head—the lush green beauty of Central Park, the amazing assortment of people of all ages and ability, the elderly guy who I locked on to and followed faithfully to the end, the misting stations that drenched me with a cooling spray, the uphill portions where I struggled with dangerous thoughts of giving up, the mysterious biker in black who looked me in the eye and said “remember to finish strong", and you know what, from God alone knows where, I found a final burst of energy and did just that.

It’s evolutionary: The answer to the growing popularity of marathons could lie in evolutionary biology. Photo by Kerstin Winterkamp/Wikimedia Commons.

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As I looked around for answers, what surprised me was that “running" itself is becoming a global phenomenon, with millions of new people taking to their feet. Take marathons. In the US, over half a million people finished a marathon in 2010, and an amazing 13 million finished some sort of road race. The New York Marathon, the big daddy on every runner’s wish list, had nearly 45,000 finishers in 2010, up from 38,000 a couple of years ago. 2010 may well be the year when marathons reached tipping point—London, Chicago, Berlin, Paris, Tokyo, all these marathons had 30,000-plus finishers for the first time. The demand is intense—the 2011 Boston Marathon (the “luxury brand" of marathons, you have to pre-qualify) sold out in 8 hours.

In India too, running is gathering momentum. Rahul Verghese, a compulsive marathoner (he has done 36 so far), and founder of Running and Living Infotainment, estimates urban India has 300,000 runners, up from 10,000 a decade ago. The 2011 Standard Chartered Mumbai Marathon—which includes a half-marathon and a 7km run—drew 38,000-plus runners.

I talked to a few runners to understand why they run. Take Penny Minges, who started running in 2007, did the Cincinnati marathon in 2008, San Diego in 2009, New York in 2010, Vancouver in 2011, and then with her son Ben, did the Gobi March—a seven-day, 250km, self-supported (you carry your own supplies) race in the desert with temperatures rising up to 54 degrees Celsius. Phew!

Why running? The excitement in her voice is palpable, and the reasons come tumbling out, but it finally boils down to two things: “the challenge" and “how it makes you feel". Explain? It is about setting a goal and pushing yourself really hard to accomplish it. Then there’s the flood of running-induced endorphins and that seems to create a special feeling. “You feel awake, clear-minded, and charged up—you may be physically tired and spent, but it’s so exhilarating, it just feels so positive," she says. “Even the pain feels good!" It must, because Penny did the Gobi March despite a stress fracture on her foot on Day 3. Incidentally, what she is describing is known as “runner’s high" and recent scientific research backs it.

Why Gobi? “It was a celebration of where we were in life," she says. She had turned 50, Ben had just graduated from college, and they wanted something special to mark it. I ask Ben what it was like? “It feels amazing—you realize you can do anything in life." That’s pretty deep—how many young people get to start life with that realization?

Hedda Fung—she is so petite, you wonder where she finds the energy—started running in 2009 to improve her cholesterol score (which got sorted in six months) and then simply kept running till she did the 2010 New York marathon, and 2011 Tokyo one. “You can’t imagine where your limit is," she says, recalling her first day when she could only do one kilometre.

“Personal challenge" and that heady “runner’s high" are compelling, but there may be a third, more primal reason that makes us run long distances. Research by evolutionary biologists Dennis Bramble and Daniel Lieberman shows that humans evolved some two million years ago into “endurance runners". Our speed may be slower, but on extremely long stretches we can outrun almost any animal (since 1980, Wales has hosted a Man versus Horse Marathon, and believe it or not, a couple of times man has won over horse). Our ancestors were after protein, and that meant running the prey down to exhaustion. Bramble and Leiberman studied fossils which show that our bodies evolved and adapted to help us run better—these adaptations included the Achilles tendon (absent in Australopithecus), the arch of the foot (evolved with Homo habilis), long legs (first appeared with Homo erectus), the ability to balance our head, and even our relatively generous behind (compared with the ape’s flat one) which helps us balance on the run.

I wonder if this recent boom in distance running is a back-to-the-future phenomenon, and hordes of human beings are simply following their evolutionary script. So go ahead, put on your running shoes, and do what you were born to do.

Radha Chadha is one of Asia’s leading marketing and consumer insight experts. She is the author of the best-selling book The Cult of the Luxury Brand: Inside Asia’s Love Affair with Luxury.

Write to Radha at luxurycult@livemint.com