Krupenye explained, "There will always be some changes in the environment that we do not witness, for example, leading us to have a false belief. Most animals probably have true and false beliefs themselves; however, the ability to understand others' false beliefs is much more restricted. Until now, there was no evidence that this skill might be shared with any nonhuman animals."
Scientists who conducted the more traditional "Sally" test on kids in the past thought that language was key to the ability, since the study involved verbally asking the children questions. More recent studies on children using eye-tracking, as for the apes, find that some 1.5–2-year-olds can pass the test.
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This all means that the ability to understand the thoughts of others, even when those thoughts include false beliefs, evolved way back in our primate past.
Krupenye said the skills might have developed "in response to the demands of living in complex social groups." He explained since males competed with others in their group for access to females, evolution likely favored the males who could outwit their competitors. In this way, the genes for social intelligence were passed on to the next generation.
"Theory of mind," he added, "allows individuals to interpret, predict, and even manipulate others' behavior."