Jonah Lehrer writes that Twitter encourages users to follow someone because they "share a set of common interests and beliefs," whereas Facebook "allows us to keep track of people we know in real life." He then applies to both sites the findings of a new paper:

What’s interesting is that the differences between Twitter and Facebook mirror a longstanding debate about how the human brain processes other people. Do we assess others based on similarity, on their devotion to the same political beliefs, TV shows and sports teams? Or do we focus instead on their closeness to us, on whether or not they’re a sibling or a third cousin or a distant friend? This might seem like a minor mystery, but it has some major implications for social cognition. Are we clannish creatures, obsessed with bloodlines and kinship? Or are we more interested in finding a group that shares our peculiar passions and opinions?

Facebook wins:

While similarity is nice – it makes cocktail conversation a little bit easier – it’s ultimately less important than mere familiarity. Of course, social cognition is an incredibly complex process, and can’t be neatly reduced to the blood flow of a single brain area. But this study helps us better understand why closeness matters, and why Facebook has more than 500 million active users, 50 percent of whom check their Facebook page every single day. We care about people we know, even if they vote for the other party.

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