INTRODUCTION

Migration is challenging in many different ways: conceptually, methodologically and as a process that is fundamental to the lives of everyone. Of the three demographic processes that change populations (fertility, mortality and migration), migration is the least amenable to definition and analysis. Yet despite considerable debate among researchers and policy makers about what sorts of spatial mobility are encompassed by the term ‘migration’, it is often the only demographic process that governments attempt to manage or regulate through specific policies. As a result, migration frequently assumes greater visibility in the media and public consciousness than the process that usually underpins growth and structural change in most populations – the balance of births over deaths, or what is termed ‘net natural increase’. It is natural increase, not net migration (the balance of immigrants over emigrants), that generally makes the major contribution to population growth.

In the eyes of some demographers, migration is the tail that wags the population dog. This metaphor seems appropriate when one considers that the total estimated net migration loss of 92 million from the less developed regions to the more developed regions between 1960 and 2010 is equivalent to just 2 per cent of the 3.85 billion growth in the estimated population of the less developed regions over the same fifty-year period. In the developed regions, the 92 million net migration gain from the less developed regions is equivalent to 28 per cent of the 324.5 million increase in their estimated population over that period.