Migrants boost productivity by expanding the workforce, allowing both them and natives to specialise. The jobs that low-skilled migrants do, as cleaners, waiters, meatpackers and so on, let people in other parts of the economy take on more skilled work. Florence Jaumotte of the IMF and colleagues find that in rich countries a one-percentage-point rise in migrants’ share of the adult population ultimately raises GDP per person by 2%.
Blocking any sort of migrant from arriving therefore lowers productivity growth. Blocking high-skilled immigration, however, is particularly damaging. Although skilled migrants make up just 5% of America’s workforce, they earn 10% of total labour income. According to Rebecca Diamond of Harvard University and co-authors, immigrants are responsible for a third of American innovation, calculated using patents, when accounting for their impact on native-born collaborators.
"Welcome to Zero Migration America", The Economist