“Suppose you have a village of 100 people. If half of them die at age five, perhaps from such childhood ailments, twenty die at age sixty, and the remaining thirty die at seventy-five, the average life span in the society is thirty-seven, but not a single person actually reached the age of thirty hale and hearty and then suddenly began to senesce.”

“Suppose you have a village of 100 people. If half of them die at age five, perhaps from such childhood ailments, twenty die at age sixty, and the remaining thirty die at seventy-five, the average life span in the society is thirty-seven, but not a single person actually reached the age of thirty hale and hearty and then suddenly began to senesce.”

— Marlene Zuk