Today, Facebook purchased Instagram – maker of the wildly popular iPhone and Android photo-sharing app of the same name – for $1 billion. That’s a lot of money for a company that’s less than two years old and has no real revenues. But viewed historically the deal is a smart one. Facebook founder Mark Zuckerberg is onto something. The human desire for self-expression – to say something as simple as “I’m here” – is insatiable, and Instagram exploits it superbly.