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In the comments to Philip's post on teenage pregnancy is a link to this wide-ranging article on the consequences of Americans' willingness to move:
The positive aspect of social and geographical mobility is obvious to most Americans: more freedom to choose and more choices. Our society is the envy of the world. Almost every other society on earth wants to imitate us. This is a worldwide social revolution in a way that Communists dreamed of but could not attain through force. But the acids of modernity do eat away at the foundations of every social order, including ours. There are no free lunches in life. There are trade-offs. There are winners and losers. The great losers in America are grandparents. In second place are grandchildren, especially those ages three to ten.