Just as some of us live longer than others, countries have different average life expectancies. At the bottom of the scale is Swaziland, the only country in the world where a newborn still cannot expect to reach age 50. And at the top is Hong Kong, where a newborn can expect to live to age 84.

In 1960, the world's countries could be divided into two groups, based on mortality. Countries in one group had low average life expectancy, from 28 years in Mali to just under 50 years in El Salvador. And countries in the second, much less populous group enjoyed higher average life expectancy — up to 73 years in Norway, Iceland, the Netherlands and Sweden.

Since then, Hong Kong has surpassed this North European group, as have Japan (84 years), Italy (83), Spain (83) and Switzerland (83). Today, the people of Hong Kong can expect their children to live 17 years longer than in 1960. Japanese newborns can expect to live 16 years longer; and newborn Icelanders can expect to live 10 years longer.