The actual source of a name is usually obvious: There's the Bible, there's the huge cluster of traditional English and Germanic and Italian and French names, there are princess names and hippie names, nostalgic names and place names. Increasingly, there are brand names (Lexus, Armani, Bacardi, Timberland) and what might be called aspirational names.

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But how does a name migrate through the population, and why? Is it purely a matter of zeitgeist, or is there a more discernible pattern to these movements?