U NDER A MAKESHIFT sunshade by a half-dry riverbed on the Indonesian island of Java, Eddie Sebastian is taking a lunch-break. It is hot and he is tired. He makes $2 a day collecting stones, breaking them with a hammer and selling them as building material. Asked if he has any better tools, he says: “Our most advanced equipment is that ‘forklift’.” He is pointing at a rusty wheelbarrow.

Mr Sebastian’s talents are wasted. Not just because he would make a fine stand-up comedian, but also because he was born in the wrong place. If he lived in a rich country, he would be operating a mechanical digger and earning $20 an hour instead of $2 a day.

Migrants who move from lower- to higher-income countries typically earn three to six times more than they did at home, according to the World Bank. The simple act of moving makes them more productive, because rich countries have better institutions, the rule of law, efficient capital markets and modern companies. Construction workers in rich countries put up better buildings because they have better tools, reliable electricity and their employer does not have to pay off corrupt local officials. Scientists in rich countries make more breakthroughs because they have better laboratories and a wider selection of other scientists to work with.

Small wonder so many of Mr Sebastian’s neighbours have migrated. A short walk up a hill from the quarry where he works is a village, Bumiayu, where the migrants’ homes are easy to spot. They are the fancy ones with multiple floors, big windows and satellite dishes. “This house belongs to a sailor,” says Idrus Dewi, a local fish farmer. “The owner of this house went to [South] Korea.” Mr Dewi is one of the lucky ones. His older sister is a nanny in Singapore. The money she sends home has paid her siblings’ school fees and provided startup capital for a variety of family enterprises.

If everyone who wanted to migrate were able to do so, global GDP would double, estimates Michael Clemens of the Centre for Global Development, author of a forthcoming book, “The Walls of Nations”. No other policy change comes close to generating such colossal rewards. If there is $90 trillion a year up for grabs, you might think that policymakers would be feverishly devising ways to get a piece of it. They are not.

In most rich countries immigration is political gelignite. Some of the biggest upheavals of the past decade—the election of Donald Trump, the rise of populism in Europe, Britain’s vote to leave the European Union—are partly driven by the fear of mass migration. Opponents of immigration everywhere make similar arguments: migrants are disruptive, strain public services, take jobs from locals and are often criminal. “I’m not a racist,” says Kevin Drake, a Brexit supporter in Essex, England. “But in school my grandkids don’t get attention because the foreigners can’t speak English and the teachers spend more time on them.” Immigration will “destroy Japan”, says Makoto Sakurai of the Japan First Party, which campaigns against Japan’s slight opening of its borders.

Few migration-sceptics can cite concrete harm that a foreigner has done to them. But nationalists around the world constantly swap anecdotes, some of them true, that reinforce their fears. In the dozen countries your correspondent visited for this special report, he kept hearing the same handful of horror stories. “German women and girls as young as three are being raped by immigrants,” warned Mr Sakurai, who lives 9,000km from Germany.

Exploiting and inflaming the fear of immigrants can win votes. Hungary’s prime minister, Viktor Orban, warns of a fictitious plot to swamp his Christian country with Muslims. Mr Trump reportedly wants an alligator moat to keep out Mexicans. Denmark has passed a law doubling the penalties for crimes in migrant “ghettos”. Immigrants are “electoral fuel”, says Andrea Costa, who runs a charity in Rome that helps them.

The anti-immigrant bug has infected non-rich countries, too. In South Africa in September, at least 12 people were killed in riots aimed at migrants from the rest of Africa. India is building camps to intern some of the 2m people it recently stripped of citizenship.

OK by me in America

This special report will ask the big questions about migration. Who is moving, where and why? What are the effects on the places they move to, the ones they leave and the migrants themselves? It will look at cross-border movement and migration within countries. It will argue, perhaps unpopularly, that the world needs more migration; that the potential gains vastly outweigh the costs, and that those costs can be mitigated with better policies.

Migrants are far less numerous than news footage of overpacked boats suggests. The UN estimates that 270m people live outside the country where they were born (of whom 90% are economic migrants and the rest mostly refugees). That is 3.5% of humanity, a share barely higher than in 1960, though some countries have been more welcoming than others.

It has become physically much easier to move, but bureaucratically much harder. Only 2% of those who arrived at Ellis Island a century ago were turned away. Now it is extremely difficult to migrate legally from a poor country to a rich one, unless you are highly skilled or a close relative of a legal resident. America’s green-card lottery last year attracted 294 applicants for each of its 50,000 slots. Partly because of Mr Trump’s efforts to make life hard for them, the net inflow of all migrants fell by 74% in 2018, to 200,000 people. Globally, many more people would like to move than can. A Gallup poll suggests that 750m people—15% of the world’s adults—want to settle permanently abroad. That includes 33% of sub-Saharan Africans and 27% of those in Latin America and the Caribbean.

To explore the costs and benefits of migration, a good spot to start is the only place where one of the populists’ stereotypes—that immigrants are largely criminals—has ever been true: Australia.■