I knew Eero Mäntyranta had magic blood, but I hadn’t expected to see it in his face. I had tracked him down above the Arctic Circle in Finland where he was—what else?—a reindeer farmer.

He was all red. Not just the crimson sweater with knitted reindeer crossing his belly, but his actual skin. It was cardinal dappled with violet, his nose a bulbous purple plum. In the pictures I’d seen of him in Sports Illustrated in the 1960s—when he’d won three Olympic gold medals in cross-country skiing—he was still white. But now, as an older man, his special blood had turned him red.

Mäntyranta, who passed away in late 2013, had a rare gene mutation that spurred his bone marrow to wildly overproduce red blood cells. Red cells convey oxygen to the muscles and the more you have, the better your endurance. That’s why some endurance athletes—most prominently Lance Armstrong—inject erythropoietin (EPO), the hormone that cues your bone marrow to produce red blood cells. Mäntyranta had about 50 percent more red blood cells than a normal man. If Armstrong had as many red blood cells as Mäntyranta, cycling rules would have barred him from even starting a race, unless he could prove it was a natural condition.

During his career, Mäntyranta was accused of doping after his high red blood cell count was discovered. Two decades after he retired Finnish scientists found his family’s mutation. A niece and nephew also had it; she was a world junior ski champion, he an Olympic gold medalist in the sport. None of the family members who didn’t have it were ski racers. Mäntyranta wasn’t doping, but you would never know that from his physiology. What does “a level playing field” mean for skiers who trained just as hard as Mäntyranta but were left behind him, gasping for air as he won the Olympic 15K race by 40 seconds, a margin never equaled at the Games before or since? Whereas Armstrong became a pariah for blood doping, Mäntyranta’s naturally doped blood is completely acceptable.

So, as the rules stand: having an incredibly rare gene mutation that boosts red blood cells—okay; training at altitude to boost red blood cells—okay; shelling out thousands of dollars to sleep in a tent that simulates altitude—okay; injecting a drug, one approved for other medical uses that causes your body to act as if it’s at altitude—you’re a disgrace. How should we draw the line? Where does a fair advantage end and cheating begin?

In one sense, the answer is simple. Sports have standard rules, not standard genes. Violating the rules, whether or not you agree with them, is cheating. Sports form the ultimate human contrivance: Take agreed-on rules, add meaning. The philosopher Bernard Suits formulated a précis describing the common heart of all sports as “the voluntary acceptance of unnecessary obstacles.” If you circumvent obstacles you voluntarily accepted, core values of the endeavor are lost. Still, as enhancement technology has transitioned from a steady march to a flat-out sprint, it is increasingly difficult to determine what is fair in one’s attempt to overcome those obstacles.

A decade ago, the World Anti-Doping Agency considered banning altitude tents. WADA’s ethics committee said the devices are “probablycontrary to the spirit of the sport.” But WADA’s scientific committees argued against a ban. Thus, today thousands of elite athletes who don’t live at altitude have the pleasure of keeping their significant others awake at night from the buzz of their altitude tent compressors.

The line is fuzzier still when it comes to augmented biology. South African double-amputee Oscar Pistorius competed on his carbon-fiber “cheetah legs” in both the 2012 Paralympics and Olympics. Is he disabled or hyperabled? Pistorius had been barred from the 2008 Olympics after a scientist commissioned by track and field’s governing body decided he had an unfair advantage. Pistorius appealed the decision before the 2012 Games, and a group of prominent scientists who studied him helped Pistorius argue that he had a disadvantage. The initial ruling was reversed. Then, after the 2012 Games two members of that scientific team split from the others and published a paper suggesting that Pistorius had an enormous advantage. In the smallest of nutshells they found Pistorius did not generate nearly the force of a typical elite sprinter but that he made up for it by swinging his ultralight carbon-fiber blades through the air faster than other sprinters could possibly swing their intact legs.

Putting a force equivalent to about five times his own body weight into the ground in a 10th of a second is the primary differentiator between Usain Bolt and you—not the speed of his leg swing, which is actually quite similar to yours. Pistorius’s blades allowed him to circumvent this main biomechanical requirement of nondisabled elite sprinting. Rather than having to put enormous force into the ground very quickly, Pistorius can leave his carbon-fiber blade on the ground longer than other sprinters, generating force all the while, and then—because the carbon fiber is so light compared with an intact limb—whip the blade through the air fast enough to make up for the time he lost while on the ground longer than his competitors. The two scientists who published that result called it the very definition of an unfair advantage. The others argued that Pistorius is still overall at a net disadvantage. For example, he clearly has trouble exploding out of the starting blocks. But science will have a tidy unified field theory before we are capable of tallying all the pros and cons of carbon-fiber blades to alight on a precise net advantage/disadvantage score. Before the 2012 Olympics I went over the data with eight independent biomechanists; all agreed that Pistorius had abnormally fast leg swing times but four felt that it wasn’t clear he had an unfair advantage, and four felt that he certainly did.

When technology replaces training or supplements biology, the lines that limn what is fair will be a bit like Schrödinger’s cat: Our collective gaze will create them. I mean that in the deepest sense. We are long overdue to ask, openly and as a society, just what it is we want from sports. Is it to see superhumans doing superhuman things? Perhaps it is. After all, you were probably aware of the most recent Super Bowl but probably not that the big game’s Most Valuable Player, Von Miller, was once sanctioned for a doping violation that reportedly included conspiring with a urine collector to skirt a positive drug test. (Miller commented that he “made mistakes” but said that his suspension did not “result from a positive test.”) And yet, football fans seem hardly to care. In bodybuilding—which actually created a separate, nondoped division—it would’ve been even less of a story; in baseball it would’ve provoked anger. In an Olympic sport, however, it would have been the apocalypse. But it’s not that fans don’t care about cheating in football, as evidenced by the interminable ripples of “Deflategate”. So let’s get this straight: A form of cheating that was employed by the MVP of the most important game and that would scandalize most sports is essentially ignored, whereas a more novel form of cheating is a big deal even though it didn’t remotely influence the outcome of a game. Make sense?

Not only is it impossible to draw a bright line in many cases regarding what should be fair on basic moral grounds, but even within already placed rules we apply different standards to different sports for reasons that are rarely articulated and difficult to understand. These judgments must be grounded in which of the voluntarily accepted obstacles we deem critical to the meaning of a given sport. We’re in for a lot of arbitrary decisions about fairness. Yes, altitude tents; no, low-friction, full-body swimsuits. The best we can do is start an earnest conversation about what it is we hope to get out of each sport. I hope that is what we are doing right here.