We are living through an unprecedented transformation in the pattern of human health, disease and death. There have been many great episodes of pestilence and famine in local populations over the ages, but there has been nothing as global and rapid as the change in the profile of human disease and longevity over the past century or so. For hundreds of thousands of years as hunter-gatherers, and subsequently in agrarian societies, our predecessors had an average life expectancy of approximately 25–30 years. Most of them died from infectious disease, and many died of malnutrition, starvation or physical trauma. A large proportion died in early childhood. Today, for the world as a whole, average life expectancy is approaching the biblical ‘three score years and ten’, and in some rich countries it has reached 80 years.

Two immediate questions arise. What has caused this radical shift in health profile? Can future health gains be shared more evenly around the world? During the 1990s, the combined burden of premature death and chronic or disabling disease was about four times greater, per 1,000 persons, in sub-Saharan Africa than in the Western world. An even more important question looms in a world that is undergoing rapid social and environmental change: can those gains in population health be sustained? To answer the second and third questions we will need to answer the first question.