How will another 220,000,000 Americans affect you? Professionally? Personally? Howabout the environment? These are the preliminary questions raised by a recent articlein The Economist. In this editorial I will try to sketch a way to look at the issues.The gist of The Economist's article is that America and Europe show strong signs ofdiverging demographically, after many years of moving in tandem. Before 1980, both weredropping so far in fertility rates (the number of children born to each woman) that bothwere below the replacement level of about 2.1 children per woman.