Evolutionary anthropologist Robin Dunbar has a famous theory that the number of people with whom one can maintain a close relationship is limited to 150 by the size of the neocortex, the part of the brain used for conscious thought and language. We know that if you are sharing with a single person you do not trust, you will not feel comfortable sharing. Path, whose service launches Monday, bills itself instead as a "personal network." Dave Morin, formerly an executive at Facebook Inc. and Apple Inc., and Shawn Fanning, co-founder of Napster, are betting that people crave more private interaction with a much smaller social circle: Path lets each user designate only 50 friends. So while we may have 5 people whom we consider to be our closest friends, and 20 whom we maintain regular contact with, 50 is roughly the outer boundary of our personal networks. From the LAT: 
 
 "You usually have about five people whom you trust most, 20 whom you consider your BFFs that you hang out with all the time and about 50 or so who are your personal network," said Morin, co-founder and chief executive of Path. To this tune, we’ve built an innovative new feedback feature we call “Seen It”. If their network contains even one person they do not trust, people tend to clam up, Morin said. Starting today, we hope that Path is the place you will always feel comfortable being yourself and sharing the story of your life with your closest friends and family via the photos you take every day with your mobile device. Practically all of us carry a camera phone, and our photos tell the stories of our lives. Simply take a photo with your camera on iPhone and add context around that moment in the form of tags for people, places and things. It lets you limit who can see the photos (no more embarrassing mumbles about why Jim didn't get an invite to the party), and you can tell who has looked at the photos. And you can view your friends' locations on a map of the world and click to see what they have posted. But he says that Facebook has just become too big, too public, and that you really don't want to share everything with hundreds of friends. Altimeter Group analyst Jeremiah Owyang said people are increasingly interested in making some of their updates more private on social networks. He also noted that, on average, Facebook users have fewer than 150 Facebook friends — still within Dunbar's number. Path may offer a compelling proposition, but it's difficult for a new social network to gain traction, he said. We hope you feel like more of your close friends are seeing life through your eyes than ever before. Because your personal network is limited to your 50 closest friends and family, you can always trust that you can post any moment, no matter how personal.
– If you were moved by Jimmy Kimmel's recent push for a National Unfriend Day, you should be glad to hear this news: New social network Path launches today, and it limits you to your nearest and dearest 50 friends. Path's limit is in keeping with the work of evolutionary anthropologist Robin Dunbar, who famously theorized that you can only maintain close relationships with 150 people—and of those, you probably only trust 50 of them, NPR notes. Developed by a former Facebook exec and a Napster co-founder, the photo-centric service's founders believe that Facebook users aren't divulging everything to their 5,000 friends, and will share more if their number of connections is limited—though they're not pitching it as a Facebook replacement, but as something meant to "ride alongside" other networks. It launches as an iPhone app that allows users to find friends using email addresses or phone numbers, then snap, post, and tag photos to create a "path" of your life, the Los Angeles Times reports.