Who Migrates? Theory, Lessons from the Past, and Latest Data

Throughout the history of humanity, migration has always existed. People have been leaving their homelands for many different reasons: push factors such as famine, war, and persecution, but also pull factors like the gold rush or – more generally – the idea of ‘lands of opportunities’ (Salt, 1976, p. 80). Accordingly, there is not one, but many theories of migration spread across several academic disciplines (Bretell and Hollifield, 2008; Han, 2006; Gupta and Omoniyi, 2007). Economists tend to focus on mechanisms that are seemingly universal, that are detached from historical or regional context. The microeconomic theory of migration postulates that the decision to migrate simply depends on a comparison of discounted earnings at home and abroad and on possible costs associated with migration. At the same time, historians point to the distinctive features of each migration wave and are sceptical with regard to universal explanations (Bretell and Hollifield, 2008, p. 7). Geographers and sociologists point to the importance of established channels of migration and migrant networks in shaping the flows. Political scientists and legal scholars point to the importance of immigration policy and law. This is not limited to the necessary conditions for living and working in a particular country, but also the rights and duties of immigrants in different countries. Interestingly, despite the lack of a unifying theoretical framework, empirical models often use variables from different theoretical frameworks that have proven significant in the past.