A decade ago, I took a group of fund managers to an assembly line at an electronics manufacturing contractor in China. We saw rows and rows of young women hunkered down, concentrating on putting together tiny parts. They had few toilet breaks, and during rest periods they had to sit at their benches.

"They're all 18," the line manager told me. "We need nimble fingers. In a few years, we will replace them with another batch of 18-year-olds."