Facebook and Yahoo are teaming up to test the famous "six degrees of separation" theory. Launched this week, the game-like experiment is based on the famous "Small World" study conducted by Harvard social psychologist Stanley Milgram in 1967. In that experiment, Migram sent letters to 300 random people in Omaha, Nebraska along with the simple instruction to relay the letter to a "target person", a stockbroker in Boston, through their friend network. The Facebook-Yahoo version works basically the same way. Starting at Yahoo!, participants connect their Facebook friend network to the experiment's network and are then given a target person to whom they must relay a Facebook message through their friends.

On the surface, the experiment seems like a pretty cool way to connect with your inner sociologist. Once you dig into the terms and conditions, though, it's actually a fairly assertive way for Facebook and Yahoo's internal sociologists to get some free research data on how users interact with each other. The San Jose Mercury reports on both angles:

The study is intended as academic social research and will be published in a peer-reviewed scientific journal, said [Yahoo's principal research scientist Duncan] Watts, a widely recognized authority on social networks.

But the results could have applications to Facebook's business, Marlow said, because the degrees of separation between individuals, and between people and commercial brands that run ads on Facebook, are important. "Facebook depends on its connectedness, and the fact that users are connected to each other and users are connected to brands, enables the diffusion of important messages, a big part of which is our advertising platform," [Facebook's chief data scientist Cameron] Marlow said.

What Marlow says about the value of connections for advertisers has always been the silver bullet for social networks' business models. It seems unlikely that Facebook and Yahoo would want to sell ads against the users participating in the experiment, but they do reserve the right to give your data to third parties. This means that any models their in-house sociologists build on based on the experiment's results could be offered up to partners--advertisers or otherwise--at any point in the future. You can delete yourself and your data from the experiment, but it requires purging the data from both your Facebook and Yahoo accountCynicism aside, the task of experimenting with the six degrees theory is pretty fun, especially on the internet. In fact, one of the very first social networking websites that started in 1997 was actually called SixDegrees.com and divided your friends up into degrees of separation. Since the launch of third-party apps, Facebook users have tried to create their own experiments. And in the absence of an ethernet connection, people love to play the very fun car-ride game, Six Degrees of Kevin Bacon.

Try it if you like, but be forewarned. It's very difficult to resist the temptation to just Google your target person and call it quits. This is, in fact, cheating and does not help Facebook and Yahoo collect information about how you connect to other humans.