How shrinking populations fuel divisive politics

In the 2000 film "Almost Famous," Cameron Crowe's comedy-drama about rock musicians in the 1970s, the character played by Zooey Deschanel gives her younger brother some advice. "Listen to 'Tommy' with a candle burning, and you'll see your whole future," she says.

I'm going to borrow that thought: Stare at the map accompanying this article with - or without - a candle burning, and you'll see your whole future.

The map shows how the number of working-age people around the world is forecast to change by 2050.

Europe's working-age population will shrink. So will that of Brazil, China, Chile, Japan and Russia, among others. And that change could have extremely negative consequences for those societies, without mitigation.

"Working-age population" can sound technical and abstract. But these are the people who staff our offices and factories, work farms, treat...