According to Brooke Jarvis in The New Yorker, for most of our history the average human life expectancy was about thirty-five years. This began to change in the eighteenth century. Since then, millions have been saved by a laundry list of innovations, starting with AIDS drugs, anesthesia, and antibiotics. Of all the innovations three stand out because they saved, not millions, but billions: artificial fertilizer, hygienic plumbing, and vaccines.