A friend recently turned 30 and at her party — along with the cake, gifts, and general merriment — I felt a responsibility to offer a warning that I would have appreciated when I reached that age.

I told her that she was about to lose many of her close friends to an insidious cultural practice that snakes its way into our lives just as adulthood is waving its hoary hand.

I'm not sure how, or when exactly, it happens, but if you are one of those infected it takes over and pretty soon you can't relate to your friends anymore.

I'm talking about running marathons.

Why is it that seemingly normal people turn 30 and then feel compelled to start training for marathons? They don't run towards or from anything, they just start running.

I can't tell you how many friends I have lost to this obsession. My birthday friend waved off my concerns as, well, insanity. But I've seen too many friends and loved ones give in to this crazy compulsion not to try to hold up a stop sign.

It doesn't make sense — 30 isn't the age to start running, long distances in particular. It's the age you start lying down.

A lawyer who used to represent injured workers told me that 30 is the age where the body starts breaking down — backs give out, knees get wobbly.

Humans actually start to shrink after 30 as muscle tone deteriorates and gravity has its way.

Most of this lawyer's clients had their first injury at around age 30. So why would we start taking up an activity that's so hard on our backs and knees, not to mention the big pump?

Researchers at places like the Mayo Clinic continue to warn that running more than 60 minutes a day can scar the heart.

Big butts

Unless a pack of wolves is chasing me, or there is a sale at Dairy Queen, there's no reason for me to run anywhere, let alone do a marathon.

A marathon runner hits his stride in Vancouver's Stanley Park. (Andy Clark / Reuters)

But I'm having trouble keeping track of all my friends who have taken up this "sport" and, despite all my protestations and my logic, it turns out we human beings are designed to run. Long distances, in fact. And for reasonably long periods of time.

Our gluteus maximus is responsible for this. In other words, as studies have found, we have big butts that do relatively little work when we're walking on flat surfaces but they come in incredibly handy to propel us during running.

According to evolutionary biologist Daniel Lieberman at Harvard University, our huge bumpers give us the balance that other bipedal animals get from tails, and they also aid in making us superior runners.

Our ability to run apparently helped in our evolution as well because while there is no way we could beat one of the other great apes in a fight we could definitely outrun them.

We also had to run to catch some of the animals we wanted to eat.

Even though many animals, like dogs and cats, run faster than us, as the distances get longer we're actually able to catch up and beat some of the fastest creatures on the planet.

Add to this the configuration of our ear canals, which give us the incredible balance needed to run on two legs, and you see why we might make ideal marathoners.

Being relatively hairless also helps. It makes it easy to get rid of excess heat.

'Marathon Boy'

Of course all that evolutionary stuff was clearly useful for our cave dwelling ancestors, but what does running a marathon really mean in our modern world, I want to ask.

Well, I may have to concede that argument as well.

I do recall that when the 9/11 attacks shook the world, New York City especially, in September 2001, the New York Marathon two months later became a symbol of perseverance.

I remember then cabinet minister John Manley going to run that marathon as a show of solidarity with our U.S. neighbours. It was potent reminder that we are in this together, for the long run.

The same can probably be said for all the charity and worthy-cause marathons that keep cropping up and occupying the ambitions of so many of my friends.

I suppose that if you think of running in socio-economic terms, it is also an incredibly democratic and accessible activity.

Unlike so many other sports, there is no expensive equipment required, just some decent shoes, I guess. No hockey-style body armour or graphite rackets, just the open road and the will to push yourself forward.

There was a beautiful and moving documentary last year called Marathon Boy about Budhia Singh, a child from the slums of India, who became a sensation for his ability to run long distances at a very young age.

He ran half-marathons when he was three, marathons and, in the most famous instance, more than 64 kilometres non-stop at four.

Budhia was loved and admired, not just for his abilities as a runner, but because of what the running represented. In a country where most live in abject poverty, to see a young boy, especially from the slums, rise to fame and notoriety for his abilities, is the great American/Canadian/Indian dream.

So maybe the marathon is more than a yuppie rite of passage, or friends going through an early mid-life crisis.

But maybe this summer, when my friends and loved ones take on the selfless task of long-distance running — either for charity or for their own insanity — I'll cheer them on and try to not to mock, from the comfort of the sidelines of course.