Yesterday was the New York City Marathon, the mecca of long-distance running, which drew over 39,000 contestants and proved that birthing a child need not get in the way of a brisk 26.2 mile tromp through the streets of this fair city. Our very own man on the street, famed podcaster Steve Mirsky, captured the following images of this bizarre urban ritual, for which an evolutionary justification follows. (File under: unweaving the rainbow.)

(Film buffs: A few scenes in The Departed were shot right around here; note the building in the upper right.)

Now maybe I'm just grumpy because the marathon's path through my neighborhood (aka straight up Williamsburg's Bedford Ave) prevented me from reaching my favorite spot for a breakfast sandwich, but to me, long-distance running has zero appeal. I mean, it's boring, it hurts while you're doing it, it hurts when you're done, and it takes up a lot of time that could be spent mastering Wii bowling. And yet people eat it up, including some of my friends of late--and then there's that guy who ran across the U.S.--which has caused me to wonder, why oh why do humans have such an itch to run?

On one level, I'm sure it's cathartic to prove you can go that far without dying like that Greek chap did, and I'm sure there are hormones involved--runner's high and all that--but that's not what I mean. Like any science nerd, I cannot comprehend human behavior without help from an evolutionary just-so story, or plausible adaptive explanation, for how we could have evolved such an ability. Science be praised, there's a good adaptive hypothesis for running that sounds like it could even be true: hunting prey.

From a story last year in Discover magazine:

University of Utah biologist Dennis Bramble and Harvard University paleoanthropologist Daniel Lieberman...argue that not only can humans outlast horses, but over long distances and under the right conditions, they can also outrun just about any other animal on the planet--including dogs, wolves, hyenas, and antelope, the other great endurance runners. From our abundant sweat glands to our Achilles tendons, from our big knee joints to our muscular glutei maximi, human bodies are beautifully tuned running machines. "We're loaded top to bottom with all these features, many of which don't have any role in walking," Lieberman says.

The story notes that temperature regulation (all those sweat glands) is key for running animals such as cheetahs, which won't push themselves past 105 degrees. (Side note: A nifty Wired story on building a better soldier describes a heat-absorbing glove that supposedly boosts muscle endurance drastically.) The researchers also point to humans' big glutes, springy leg tendons, well-balanced noggins and longer legs, which would (they contend) make running--but not necessarily walking--more efficient.

The fossil evidence at least doesn't contradict the notion that endurance-running was a driver of human evolution. According to a 2004 Nature paper by Bramble and Lieberman, humans exhibit a slew of running-related traits lacked by our australopithecine forebears such as the 3.2-million-year-old Lucy, who seem to have been too squat and chimplike to run for long stretches.

And why would we have needed sustained speed? Why, to fuel our growing brains by catching prey rich in protein and fat, naturally. The obligatory anthro evidence comes from run-alongs with Bushmen hunter-gatherers in the central Kalahari Desert in Botswana, who, after being sure to hydrate themselves properly like any good runner, chase a prey animal to exhaustion, maintaining speeds and for distances comparable to those of competitive marathoners.

The caveats (again from Discover):

Functional morphologist Brigitte Demes, at the State University of New York at Stony Brook, notes that the gluteus maximus is absolutely essential for rising from a squatting posture at rest or during foraging, so it might not have evolved just for running. Stony Brook anatomist Jack Stern, famed for analyses of how Lucy walked, says it's a tough call to classify the Achilles tendon as an adaptation for jogging. Longer legs evolved in many animals through the extension of lightweight tendons rather than heavier muscle, thus producing a limb that took less effort to swing - a change that would save energy during walking, Stern says.

None of which strikes me as particularly damning to the endurance running hypothesis, given that evolution would have had to satisfy a set of competing environmental pressures. Here's a link to some other critiques.

In closing, all good behavioral just-so stories end by examining how the long ago-evolved trait fits into modern life. So pray tell, what prey (chortle) are we chasing down today? Mirsky's investigative photojournalism suggests an answer:

Which of course sustains yet another key mammalian behavior...

Consider that territory marked! ...or...

Think about that the next time a marathoner tries to high-five you. ...or...

Aren't you glad I didn't put this post behind a... pee-wall? (Oh snap!)