As part of my research, I have come up with ten building blocks needed for reasoned analysis of migration. Some are straightforward; others are analytically tricky and you will need to chew on them. Indeed – with apologies for a self-serving remark – you will need to read the book. [Exodus: How Migration is Changing Our World]

Block 1 Around 40 per cent of the population of poor countries say that they would emigrate if they could. There is evidence that suggests this figure is not a wild exaggeration of how people would behave. If migration happened on anything approaching this scale, the host societies would suffer substantial reductions in living standards. Hence, in attractive countries, immigration controls are essential. 

Block 2 Diasporas accelerate migration. ... These links cut the costs of migration and so fuel it. As a result, while diasporas are growing, migration is accelerating. 

Block 3 Most immigrants prefer to retain their own culture and hence to cluster together. This reduces the speed at which diasporas are absorbed into the general population. The slower the rate at which they are absorbed, the lower the rate of immigration that is compatible with stable diasporas and migration. By design, absorption is slower with multicultural policies than with assimilative policies. 

Block 4 Migration from poor countries to rich ones is driven by the wide gap in income between them. ... Migrants are escaping the consequences of their systems but usually bring their culture with them. 

Block 5 In economic terms, migrants are the principal beneficiaries of migration but many suffer a wrenching psychological shock. ... 

Block 6 Because migration is costly, migrants are not among the poorest people in their home countries. The effect on those left behind depends ultimately on whether emigrants speed political and social change back home or slow it down. A modest rate of emigration, as experienced by China and India, helps, especially if many migrants return home. However, an exodus of the young and skilled – as suffered by Haiti, for example – causes a haemorrhage that traps the society in poverty. 

Block 7 In high-income societies, the effect of immigration on the average incomes of the indigenous population is trivial.

But, what about the costs of the indigenous population? What everybody is interested in is not incomes or costs, but their net: standard of living.

Block 8 The social effects of immigration outweigh the economic, so they should be the main criteria for policy. These effects come from diversity. Diversity increases variety and this widening of choices and horizons is a social gain.

Yet diversity also potentially jeopardises co-operation and generosity. Co-operation rests on co-ordination games that support both the provision of public goods and myriad socially enforced conventions. Generosity rests on a widespread sense of mutual regard that supports welfare systems. Both public goods and welfare systems benefit the indigenous poor, which means they are the group most at risk of loss. As diversity increases, the additional benefits of variety get smaller, whereas the risks to co-operation and generosity get greater. ... 

 

Block 9 The control of immigration is a human right. The group instinct to defend territory is common throughout the animal kingdom; it is likely to be even more fundamental than the individual right to property. ... It sometimes makes sense to grant the right to migrate on a reciprocal basis. Thousands of French people want to live in Britain, while thousands of Britons want to live in France.  

Block 10 Migration is not an inevitable consequence of globalisation. The vast expansion in trade and capital flows among developed countries has coincided with a decline in migration between them. 

These ten building blocks are not incontrovertible truths but the weight of evidence favours them to varying degrees. If your views on migration are incompatible with them, they rest on a base too fragile for passionate conviction.