Sarah Blaffer Hrdy, in Mothers and Others, needs to figure out how humans developed intersubjectivity or a "theory of mind" - that is, the ability to understand what other people are thinking and feeling. She says that there are two main theories. One, that mothers needed to develop a capacity to read the minds of their pre-verbal babies. Two, that people needed to develop a "Machiavellian mind" to understand and anticipte the plans of their rivals. To these she adds a third strong motivation: babies need to understand what their caregivers are thinking and feeling. As Hrdy puts it, a baby's first job is to get mom addicted to nurturing, and that requires that babies need to know how to read mom.
I was surprised that Hrdy did not emphasize how gendered these theories are. When she names the chief proponents of the mother's mind-reading theory and the Machiavellian mind theory it is easy to see that the former are women and the latter are men. Hrdy notes regularly that as a mother she is very attentive to how babies interact with mothers.
I think these gender differences in theories of mind reading strengthen the case that they are true. If men, women, and children all have strong and distinct reasons to do something, that makes me more convinced that it is really true. Moreover, the different kinds of mind reading complement one another. My focus is on mate selection and marriage. Women select men who can provide resources; men who can anticipate rivals and cooperate with allies should be better at getting resources. Men select women who will be good nurturers; women who can understand what their families need even when the need has not been said in words would be better at nurturing.
I would add one more reason that humans need intersubjectivity. Women need to read whether men are really committed before they take the great risk of having children with them. And men, to a lesser extent, need to be confident that the women they marry will stay faithful to them. Women rely on mind reading more than men do, and often expect men to do the same. This leads to many miscommunications in courtship and marriage.
Nonetheless, human beings - women, men, children - have a strong need to be able to understand what other people are thinking and feeling, even without words. Whether, as Hrdy thinks, this capacity evolved or if we acquired it some other way, it is still a skill useful enough to keep. Which is reason enough for human beings to do it more, and more effectively, than any other creatures.