Tyler Cowen always finds interesting ways to look at things. As he posts here, population in Europe will continue to age and the young will increasingly come from Africa and Asia to work.
Here’s Tyler’s Upshot article and it’s not complicated – if you’re a rich country, you need immigrants. Just trying to have more babies isn’t really a strategy.
Tom Barnett puts it this way,
The core countries have the money and the jobs, but not the people. Outside the core, they have the people, but not the jobs. We’re gonna need someone to turn us over in our hospital beds.
Here’s Barnett talking about the flow of people (around 6:30 mark is where he talks about the job flow from the gap to the core).
Last but not least is the populationpyramid.net site. Here you can play with any country you like from now to 2100. The key to population pyramids is their shape. Japan’s in serious trouble. They’re not replacing their dying and they won’t follow Cowen’s advice to allow immigration.