Peak performance has always been about getting as close to your genetic potential as possible. The limits of your training, nutrition, and recovery are dictated by your DNA. But what if they weren’t? What if you could change the genetic code you were born with? As sequencing DNA gets cheaper and faster, and gene-editing tools get more precise and easy to use, we’re progressing toward a world where we might all have perfect DNA for our chosen sport—and be able to change it whenever we want. But getting there will be risky. In this final installment of our four-part look at the science of performance, Outside editor Christopher Keyes looks at the efforts of Josiah Zayner, who is taking a damn-the-torpedoes approach to doing everything he can to bring gene-editing to a laboratory—or even a garage—near you.