The human smile may reveal more about a person than initially meets the eye, psychology professor Marianne LaFrance claims.

Her new book, “Lip Service: Smiles in Life, Death, Trust, Lies, Work, Memory, Sex and Politics,” published August 8, explores the place of smiling in social interactions. LaFrance, who has co-authored two previous books, is a social psychologist whose research focuses on non-verbal communication, particularly facial expressions, and their relation to gender. The News sat down to talk with her Tuesday about her work on smiles.

Q Why study smiles?

A Smiling seems on the surface to be so straightforward, so uncomplicated, that most people tend to underestimate it in terms of its impact and the role it plays. If you show people a picture or a short video of someone smiling, the usual response is, “So…? The person is smiling, they’re probably happy, end of story.” But in fact that’s just the beginning of the story.

The smile may be the most underestimated social expression that we as humans have. It is used in many social situations, it serves many social functions, and it often has little to do with what might be considered positive, happy, amused, contented feelings, and has a lot more to do with keeping the social machine operating relatively smoothly.

Q You’ve studied the relationship between gender and facial expression. What are the differences between men and women when it comes to smiles?

A The general finding is that girls and women tend to smile more frequently than boys and men. What turns out to be more complicated is the question of why that is the case. There is some indication that females are more socially attuned and responsive than males, and part of being responsive is smiling. Another reason has to do with expectations for femininity. Females are supposed to smile more than men — it’s not just that they do, but there is a prescriptive stereotype that they should.

Another big reason is that many of the social roles and occupations that women have are service occupations and roles. Women are often in those jobs in which part of the service is to smile. Another explanation is that it may have something to do with being, more often than not, in a position with low power. The theory here is that smiling often connotes a submissive or deferential position. Though there have been changes, it is still the case that women in general have less power than men.

Q How good are people at telling the difference between a real and a “fake” smile?

A Even little kids are relatively good at it if you ask them to take a look at a photograph and go with their hunch. But in most social situations we’re not paying close attention. If we were paying attention we might be able to detect a “fake” smile or a deliberate smile, as we prefer to call it, but most social relationships depend on treading lightly. Everybody agrees to let things go.

A second aspect to “faking” is that deliberate smiles are as natural as spontaneous smiles. That is, we are socialized how to smile — to get us through tough situations, to convey a greeting, to reduce conflict when the tension is high. Though some smiles could be considered fake in that they are deliberately adopted, they are socially genuine, because they’re there to smooth relationships.

Q In your book you argue that smiling isn’t just helpful to smooth over social interactions; it’s actually crucial for babies to survive and develop social skills. Can you talk about why?

A Well, the first social smiles that babies show have nothing to do with positive feelings. They have to do with an evolutionarily designed mechanism to secure attachment from unsuspecting adults, who get taken in and fall in love with the baby and vow eternal commitment to the baby. Babies are born ready to smile, and the smile then gets molded and transformed over the first few months and years into something that is culturally and socially recognizable and appropriate. And kids who don’t develop that often tend to be kids who have problematic social relationships. Smiling clearly plays a part in communicating that one is a normal, decent human being who can be trusted.