Psychologist Robin Dunbar's assertion that the human brain is hardwired to cope with social groups of about 150 people is being put to the test by social networks. Some networks, such as Path, embrace Dunbar's work and limit their users' contacts accordingly; others, such as Facebook, see such social limits as challenges to be overcome. "We do talk about it. In a lot of contexts it's a compelling framing of some of the data that we have about people's relationships," Facebook's Cameron Marlow says.
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