We all age chronologically with the passage of time, but what about our bodies? Is physiological aging inevitable too? A growing cadre of biologists is starting to say no, thanks to developments in the field of epigenetics, which studies not our DNA itself but the processes that determine how our genes “express” themselves in directing our cells throughout our lives.

If you think of your inherited genetics, your DNA, as a piano keyboard, then epigenetics determines how the keys play music. The primary players in this concert...