Why is the gap between rich and poor in America yawning ever wider?

The issue is urgent. As my colleague Annie Lowrey writes, there is growing evidence that income inequality impedes economic growth.

And one interesting explanation boils down to the high price of housing.

A recent paper by researchers at Harvard University argues that the prohibitive cost of living in the areas with the greatest economic opportunities has forced low-wage workers to migrate instead to areas with inferior opportunities.

“The best places for low- and high-skilled workers used to be the same places: California, Maryland, New York,” said Peter Ganong, a doctoral student in economics, who wrote the paper with Daniel Shoag, a professor of public policy. “Now low-skilled workers can no longer afford to move to the high-wage places.”

In this account, people aren’t moving to the Sun Belt because they want to live there. They are moving because they can’t afford to live in Boston. And the result isn’t just second-best for them; it also slows the pace of economic growth.

Basically, the economy works best when people can move where their skills are most valued. But for low-skill workers, the high price of housing means the cost of living in those places often exceeds the benefits of working there.

The trends are beautifully illustrated by three time-lapse graphics.

The first shows that average incomes by state converged between 1880 and 1980 as low-skilled workers moved to wealthier states. The second shows the pattern of migration, which has changed significantly over the last 30 years.

The third shows the increase in land-use regulations in rich states.

And here’s the crucial point: It doesn’t have to be this way. High housing prices are the result of public policies that discourage new development. Those policies are generally embraced by the residents of wealthy areas, who benefit, at least in the short term, from restrictions on the supply of new housing. But this paper is one more reason to worry about the long-term economic consequences.