The aim of this book is to reveal the demographic forces that shape our modern world and evaluate the policies that have been devised to control and affect these forces.

The term demography was first used in a book by the Belgian Achille Guillard, published in 1855 under the title Elements de statistique humaine ou demographie comparee (Elements of Human Statistics or Comparative Demography). The term is now commonly used to refer to important trends such as rising population, ageing population and changes in life expectancy and birth rate. Demography is also a flourishing academic discipline producing a statistically sophisticated body of work. This book draws heavily on the work of professional demographers, clarified for a more general audience. However, the focus of this book is less on the statistical modelling of population trends and more on their economic, political and social implications.

Demographers sometimes use the term “vital statistics” to refer to population-related numbers. “Vital” has many meanings, but, for me, two stand out from the Oxford English Dictionary's (OED) numerous definitions: “Imparting life or vigor” and “Supreme importance”. The vital statistics of a society are, as the OED definitions imply, of “supreme importance”. They are not simple reflections of social forces; they impart the life and vigour that help direct these changes. They are not just dependent variables. They are independent variables that play a significant role in shaping specific societies and global trends. Demography, in other words, is of great importance, perhaps best summed up in the phrase “Demography as Destiny”. It is often attributed to Auguste Comte (1798–1857), but no formal citation has ever been found. Demography may in fact be destiny, but not in a simple mechanistic way. The relationships are often more subtle and elusive to the shallow analysis. We need to delve below the surface to reveal demography's powerful influence. But we should be wary of too mechanistic a narrative. The book avoids the simple causal argument that demography is the major source of all social changes but instead shows the complex interactions between social and demographic processes. The book highlights how demography is important but avoids the simplistic notion that it is a predetermined destiny.