Play is fundamentally social. Science used to believe that the reason play existed across the entire mammal kingdom was because it served as a form of practice for skills. But it turns out that if you separate and prevent tiger cubs, say, from playing, they grow up quite able to hunt, fight, stalk, and so on (this is from a study by Tim Caro cited in Play: How it Shapes the Brain). They pick up these skills in other ways. What they don’t learn to do — and can never learn — is how to get along with others of their kind. (This doesn’t mean that play doesn’t help skill-building; there’s plenty of science on that too). Play is fundamental to learning social skills, and social skills are a key survival trait because they are an evolutionary benefit; teams working together can accomplish things that individuals working alone cannot.

Humans have a pattern to their social relationships. Simply put, it falls into a pyramid: around 5 really intimate friends, 15 that are less so, around 50 that are more distant, and then an average total of around 150 social connections. This 150 figure is known as Dunbar’s Number, and to be clear, there’s a lot more nuance to it than “you can only have 150 friends.” (Christopher Allen has some excellent writing on misapprehensions of what Dunbar’s Number means, and I’ve discussed social graphing several times on my blog). This kind of increasing intimacy has been found by Dunbar himself in a large study of tens of millions of phone records; and also by those studying games, such as Nick Yee and Nic Ducheneaut in their examinations of guild subgroups in World of Warcraft.

The variable here is trust. Human relationships progress through a set of stages which are pretty well understood. We start out tentative, trying to see what we have in common, then we gradually start relying on one another, and eventually come to trust one another. This is called “Social Penetration Theory,” by the way, and comes from actual experimental data. One thing that the data showed is that high trust doesn’t necessarily mean high trust in every facet of a life. Which leads to the fourth point:

Trust is domain-specific. Just because you implicitly trust your trapeze partner with your life doesn’t mean you trust them with, say, your finances. Social Penetration Theory uses the words “breadth” and “depth” to refer to the spread of domains in which you might have trust versus the degree of trust you might have. It’s a mistake to assume that we might build a game that requires incredibly high trust in your teammates, and that therefore the players of the game will come to trust one another with, say, their children’s well-being. (In fact, a huge portion of the social mechanics that I curated into my talk of that title are in fact ways of dealing with a lack of domain trust).