An excerpt from my genetics professor: "Even in the absence of mutagens, an average gene will mutate about once in a million generations. ~10^16 cell divisions

An excerpt from my genetics professor: "Even in the absence of mutagens, an average gene will mutate about once in a million generations. ~10^16 cell divisions occur in a typical life span so somewhere in cells that are part of you each of your genes has mutated 10^10 times (hence cancer)."