More specifically, imagine the simplest case of a population of a constant size - say a million (the approximate size of the Holy Land at the time of Jesus).

BBC: Family trees: Tracing the world's ancestor

And then there is the near constant temptation of king-size burgers, thick shakes and other high-calorie foods.

WSJ: Can a Whole City Stick to a Diet? Fat Chance

The one constant of the iPhone for its five-year history has been the screen size.

ENGADGET: iPhone 5: the rumor roundup Mobile