The Sports Gene: Inside the Science of Extraordinary Athletic Performance (25 page)

Suddenly, Mackey’s competitors wanted to copy the marathon style. Overnight his kennel went from home of cheap castoffs to a yard full of coveted bloodlines, with dogs worth four figures each, at least. (According to Tonya Mackey, Zorro’s son Hobo was purchased by another musher and then “tossed all around Norway breeding, at a couple grand for each breeding.”) In 2008, Mackey won the Iditarod again, his second of four straight. In a race a few weeks later, a drunk snowmobile driver rammed his team. Zorro had to be airlifted to Seattle with three broken ribs, a bruised lung, internal bleeding, and spinal damage so severe he couldn’t stand.

Zorro survived, but a veterinarian ordered that he be retired from breeding and racing. Mackey built Zorro a doghouse in the yard, but quickly saw that his relentless runner would whine and tug at his chain if he was passed over while other dogs were taken out on a run. So Mackey built him the “condo on the hill,” his fenced-in area in front of the house. “He’s still the badass in the kennel,” Mackey says. “He’s my main man even though he doesn’t run. He holds a very, very special place in my life and heart.” And, more important, in the gene pool in his front yard.

•

The idea that dogs can be bred to win a race is no revelation. Darwin himself marveled at the ability of dog breeders to cultivate almost any
trait they wanted. Breeding for speed in racing whippets has been so intense that over 40 percent of the dogs in the top division have what is normally an exceedingly rare myostatin gene mutation (the “Superbaby” mutation).

In the late nineteenth and early twentieth centuries—particularly during the Klondike Gold Rush—when the seaports and rivers of Alaska were frozen solid, sled dogs were the main source of transport for everything from mail to gold ore. Breeding for strength, endurance, and resistance to cold proceeded in earnest, until snowmobiles came into fashion. When dogsled racing gained popularity with the rise of prize money following the first Iditarod in 1973, breeding for athleticism became a serious business. Pointers, salukis, and a bundle of other breeds were mixed into a genetic stew that had traditionally included Alaskan malamutes and Siberian huskies. It worked.

The winners of the first two Iditarod races took more than twenty days to finish. Two decades of breeding later, mushers were finishing in half that time. Alaskan huskies morphed into athletes unique on the planet. Even before training, an elite Alaskan husky can move four to five times as much oxygen as a healthy, untrained adult man. With training, top sled dogs reach a VO
₂
max about eight times that of an average man, and more than four times higher than a trained Paula Radcliffe, the women’s marathon world record holder.

Sled dogs were bred for everything from a voracious appetite—they eat ten thousand calories a day during the Iditarod—to webbed toes ideal for traveling atop snow, to a pulse rate that settles quickly at a moment’s rest. Perhaps the most remarkable bit of biology bred into Alaskan huskies is the ability to adapt almost instantly to exercise. As in humans, when sled dogs start training, they deplete the energy reserves in their muscles, undergo an increase in stress hormones, and damage cells. Human athletes experience this as fatigue and soreness, and must rest to allow the body to adapt to the exercise before coming back to training or racing. But the best sled dogs adapt
on the run.
Whereas humans have to alternate exercise and rest to get fit, premier Alaskan
huskies get fit while barely stopping to recuperate. They are the ultimate training responders.

In 2010, Heather Huson, a geneticist then studying at the University of Alaska, Fairbanks—and a dogsled racer since age seven—tested dogs from eight different racing kennels. To Huson’s surprise, Alaskan sled dogs have been so thoroughly bred for specific traits that analysis of microsatellites—repeats of small sequences of DNA—proved Alaskan huskies to be an entirely genetically distinct breed, as unique as poodles or labs, rather than just a variation of Alaskan malamutes or Siberian huskies.

Huson and colleagues discovered genetic traces of twenty-one dog breeds, in addition to the unique Alaskan husky signature. The research team also established that the dogs had widely disparate work ethics (measured via the tension in their tug lines) and that sled dogs with better work ethics had more DNA from Anatolian shepherds—a muscular, often blond breed of dog originally prized as a guardian of sheep because it would eagerly do battle with wolves. That Anatolian shepherd genes uniquely contribute to the work ethic of sled dogs was a new finding, but the best mushers already knew that work ethic is specifically bred into dogs.

“Yeah, thirty-eight years ago in the Iditarod there were dogs that weren’t enthused about doing it, and that were forced to do it,” Mackey says. “I want to be out there and have the privilege of going along for the ride because they want to go, because they love what they do, not because I want to go across the state of Alaska for my satisfaction, but because they love doing it. And that’s what’s happened over forty years of breeding. We’ve made and designed dogs suited for desire.”

Several mushers I spoke with suggested that sled dogs may have maxed out their physiological capacity and are no longer getting faster or hardier, and that the improvement in race times is now entirely down to how long the dogs are eager to pull without rest. “The dogs are in control,” says Eric Morris, the biochemist and musher. “That’s why we
breed dogs that want to do it . . . it’s something I had to learn through trial and error, and time, and speaking and working with other mushers, to find out what all the great ones know. The great mushers know how to breed a dog that has drive and the desire to pull, and then they foster and develop that desire.”
*

•

Scientists who breed rodents for their desire to run have proven that work ethic is genetically influenced. One of the leaders in that field has been Theodore Garland, a physiologist at UC Riverside. For more than a decade, he has been offering mice a wheel that they may hop on or shun at their discretion.

Normal mice run three to four miles each night. Garland took a group of average mice and separated them into two subgroups: those that chose to run less than average each night, and those that chose to run more than average. Garland then bred “high runners” with other high runners, and “low runners” with other low runners. After just one generation of breeding, the progeny of the high runners were, of their own accord, running even farther on average than their parents. By the sixteenth generation of breeding, the high runners were voluntarily cranking out seven miles each night. “The normal mice are out for a leisurely stroll,” Garland says. “They putz around on the wheel, while the high runners are really running.”

When mice are bred for endurance capacity—not voluntary running, but when they are forced to run as long as they physically can—successive generations have more symmetrical bones, lower body fat, and larger hearts. In his voluntary-runner breeding program, Garland
saw body changes, “but at the same time,” he says, “clearly the brains are very different.” Like their hearts, the brains of the high runners were larger than those of average mice. “Presumably,” Garland says, “the centers of the brain that deal with motivation and reward have gotten larger.”

He then dosed the mice with Ritalin, a stimulant that alters levels of dopamine. Dopamine is a neurotransmitter, a chemical that conveys messages between brain cells. The normal mice, once doped, apparently derived a greater sensation of pleasure from running, so they started doing it more. But the high runners, when doped, did not run more. Whatever Ritalin does in the brains of normal mice is already occurring in the brains of the high-running mice. They are, quite literally, running junkies.
*

“Who says motivation isn’t genetic?” Garland asks, rhetorically. “In these mice, it’s absolutely the case that motivation has evolved.”

Researchers around the world have begun to explore locations on the genome that differ between marathon mice and their normal counterparts, and specifically to home in on genes related to dopamine processing that might impact the sense of pleasure or reward a mouse gets from a particular behavior.

Of course, they aren’t doing this simply to understand why rodents want to run. The ultimate goal is to learn about human gym rats.

•

Pam Reed was up on top of the parking garage at LaGuardia Airport in Queens, again. Her flight out of New York City was delayed, and she was never one for sitting still. While disgruntled travelers jostled for electrical outlets and cushioned seats, their bags trundling behind
them, the fifty-one-year-old Reed popped in her earbuds and headed for the top deck of the parking garage.

She breathed in the thick summer air. Reed stashed her luggage in a corner and started running. Immediately, a placid calm dripped through her body. For a good hour, she ran around and around in tight circles, each lap no more than 200 meters. It certainly wasn’t because she needed the fitness.

Just the previous day, Reed had finished the U.S. championship Ironman triathlon in New York City in 11 hours, 20 minutes, and 49 seconds, good enough to qualify for the world championship in Hawaii. A week before that, she participated in a relay race in which her leg consisted of eight continuous hours of circling a track. Two weeks before that, she spent 31 hours running en route to becoming the second female finisher at the 2012 Badwater Ultramarathon, a 135-mile race that starts in Death Valley, and that Reed has won, twice.

Reed’s flight out of LaGuardia eventually left, and the next weekend she completed the Mont-Tremblant Ironman in Québec in 12 hours, 16 minutes, and 42 seconds. The weekend after that, she had “only a marathon,” she says, never mind that it was through the Tetons, in her home of Jackson Hole, Wyoming.

This isn’t some masochistic running binge, it’s life for a woman who once ran three hundred miles without sleeping, and in 2009 spent six days running 491 laps around a drab one-mile loop in a park in Queens.

When she was an eleven-year-old in Michigan, Reed was smitten by her first sports love while watching the 1972 Olympics on TV: gymnastics. “I was obsessed,” Reed later wrote in her autobiography,
The Extra Mile.
“I practiced gymnastics every minute that I could, in the basement, off the couch, wherever I happened to be.” In high school, Reed turned to tennis, and, as usual, threw herself into it the way a Navy SEAL throws himself out of a plane—with gusto. Part of her training was a minimum of one thousand sit-ups a day. She went on to play varsity tennis at Michigan Tech. When she later moved to Arizona—she
owns and directs the Tucson Marathon—she worked as an aerobics instructor so that she could have access to the health club’s pool. Naturally (for Reed), she fell in love with her second husband as the pair trained together for an Ironman triathlon. Reed has often wondered about the source of her relentless drive to be in motion.

Her father was tireless. He used to rise at 3:30
A.M
. to head to work at an iron mine, and when he returned home in the afternoon he would go straight to building an addition to the house or tinkering on the car. According to family lore (“absolutely true,” Reed says), her grandfather Leonard once got into an argument at a family gathering in Merrill, Wisconsin, and stormed out in a huff. He kept walking. The entire three hundred miles back home to Chicago.

“Running for three hours every day might put some people in the hospital,” Reed writes in her book, while noting that she finds peace of mind in extreme activity. “I am certain that
not
running for three hours every day would very quickly make me ill. . . . While nobody’s forcing me to do this, it’s not really a choice, either. There’s something in my nature that makes it really hard for me to sit still . . . being temperamentally attuned to perpetual motion makes me pretty uncomfortable on long car trips or in sedate social settings.” (Reed’s son Tim contrasts himself to his mother: “I only like to run for maybe two or three hours max.”) One of Reed’s current goals is to set the women’s world record for running across America, which she plans to do at a pace of two marathons a day.

“When I don’t do this,” Reed says—and by “this” she means running three to five times a day—“I feel horrible. I had C-sections, and three days after them I was running. . . . It’s who I am. I totally love it. As I get older, I have to say, I can sit still a bit longer, but it’s not comfortable.”

In her book, Reed astutely ponders whether she might be the human version of the rodents from an experiment at the University of Wisconsin in which mice bred for voluntary running were restricted from running, and then had their brain activity measured. Brain
circuitry similar to that which is active when humans crave food or sex, or when addicts crave drugs, was activated in the high-running mice that were denied the chance to run, and they became agitated. The researchers presumed that when the mice were deprived of running their brain activity would decline. Instead, it went into overdrive, as if the mice needed exercise to feel normal. The longer the distance a particular mouse was used to running, the more frenetic its brain activity became when it was made to sit still. As with Garland’s mice, these rodents were genetic junkies for exercise.

Pam Reed is an outlier by any measure. But a seemingly compulsive drive to exercise is hardly unique among distinguished athletes. Consider Ethiopian Haile Gebrselassie, who has set twenty-seven distance running world records: “A day I don’t run, I don’t feel good,” he says. Or Floyd Mayweather Jr., the undefeated boxing champion, who has been known to jolt awake in the middle of the night and force his bloated entourage to meet him at the gym for a workout. Or Steve Mesler, a member of the 2010 Olympic four-man bobsled team that won the first U.S. gold in sixty-two years. He retired afterward, but says he “feels anxious” when he takes a break from working out even now. Or Ironman triathlete Chrissie Wellington or high jumper Stefan Holm, both of whom claim addictive personalities that they channeled to their training.