The concept of theory of mind has its roots in evolutionary biology. The term was first coined in a 1978 paper by primate researchers who concluded that higher apes like chimpanzees couldn't understand the mental states that lead to action on others' parts, though later research has found that they likely can [source: Call and Tomasello].
So what is the evolutionary benefit of theory of mind? As communications professor Francis F. Steen describes it, by considering others' motives to predict their actions, an animal can determine whether a predator is moving toward it to attack and eat the animal. Conversely, when it appears the predator is too hot to move on a particularly warm day, such a mechanism allows the animal -- which is likely hot, too -- to rest easy as well and not expend any unnecessary energy running away from a predator that has no interest in pursuing it [source: Steen]. Anyone who has seen footage of a lion and a gazelle lying down, panting and watching one another only yards apart has seen this mechanism in action.
But comparing a gazelle's ability to predict whether a lion is in a mood to attack with human folk psychology is slightly off base. Cognitive researchers don't necessarily believe that animals like gazelles and lions possess theory of mind. They consider only humans and most likely higher apes in possession of this far more advanced intellectual analysis. More to the point, if you've ever looked at a lion and considered that it looked happy or that it wished it were free, you've just proven yourself capable of the kind of higher order thinking that theory of mind is based on.
In fact, the example using the gazelle is a rival to theory of mind as an explanation for how humans carry out folk psychology. This animalian concept, called mental simulation, says that we predict others' goals and actions based on creating mental constructs of what we would do if we were in their shoes. We use our past experiences to create a mental model of the situation, essentially using our brains' processing power to analyze the available data and then make our prediction [source: Marraffa].
What differentiates theory of mind from simulation and other explanations for how we arrive at our ability to carry out folk psychology is fairly nuanced. Theory of mind says that we practice folk psychology by forming ideas about what other people believe at any given moment. And recent findings in autism research have lent support to the theory-theory.