It starts with a single gene, out of some 20 to 25,000, coding for the more than 30 trillion cells in a human body. Take the length of the DNA in those cells, unravel it, and you have a distance of more than 400 lengths from the sun to the Earth. The human genome has 6 billion data points of information. Six billion ways for something to go incredibly right — or incredibly wrong. ... Sorting through these possibilities is the job of Stanford University scientist Euan Ashley. The 45-year-old Scotsman is a cardiologist, a systems biologist, and one of the leaders of a new, integrated approach to the science of genetics. He led the first team to clinically interpret a full human genome; he’s involved in attempts to sequence cancer genomes for personalized treatment and to analyze the genomes of individuals who have rare and unknown diseases. But for the last several years, his work has focused on a specific mystery. He is looking for superhero genes ... “We’re interested in truly the fittest people on the planet,” he explained. Though there are many factors that may make someone elite, his team made the decision to select athletes on the basis of a single, objective physiological variable: the maximum amount of oxygen a body can use, or VO2max. VO2max is considered one of the most important markers not only for athletic success, but for overall health: It’s such a crucial indicator of cardiovascular function that it is used to determine whether someone requires a heart transplant. VO2max has also been measured in the same way for half a century, which means it can be a useful comparative point. ... To be a part of the study, men need to test at a VO2max that exceeds 75 milliliters of oxygen per minute; for women, the cutoff is 63. Fewer than .00172 percent of the population qualify.