A British actuary, Benjamin Gompertz, noticed this pattern back in 1825, and ever since it's been called the Gompertz law of human mortality — yes, death creeps closer, but it creeps closer in orderly steps (for humans about every eight years).

Roughly every eight years, the odds that a human will die doubles. This is Gompertz law of mortality.

This led physicist Brian Skinner to try to figure out why, and he made a surprising discovery.

OK, so this happens. The pattern, says Brian, "holds across a large number of countries, time periods and even different species. While actual average lifespan changes quite a bit from country to country and from animal to animal, the same general rule that 'your probability of dying doubles every X years' holds true."
But here's the dangling question: Why the regular interval? Why eight years for humans?
Why eight years?
Brian's answer: "It's an amazing fact, and no one understands why it's true."