Smiles are often for show, a faking of positivity for the purpose of social reassurance. An attempt, if you will, to influence others into thinking that we are experiencing positive affect (Addyman et al., 2018). Observers have suggested that genuine smiles accompany an activation of the zygomaticus major muscles, pulling the corner of the lips up and back towards the ears (Martin et al., 2017) whilst the orbicularis oculi contracts, producing crows’ feet around the eyes. Yet the so called ‘true’ or Duchene smile is not as reliable as often thought (Girard et al., 2021).
Whilst such a smile is difficult to fake, it’s not impossible (Gunnery & Hall, 2014), and, in any case, despite its ‘genuine’ tag, a true smile doesn’t necessarily reflect internal happiness. Genuine smiles also express feelings of disappointment (Kromm et al., 2015), embarrassment (Keltner & Buswell, 1997), surprise (Lei & Gratch, 2019), failure (Ohta et al., 2021), nervousness (Ambadar et al., 2008), and frustration (Hoque et al., 2012). There are at least 19 different types of smiles, each with a different purpose, in addition to countless compound (combined) versions. Smiling is also used to direct conversation (Kaukomaa et al., 2013).
It seems that we are actually quite good at realising that many smiles are not reflections of positive emotion (Martin et al., 2021). People may even respond aggressively to certain types (Kawamoto et al., 2013). And, of course, just as smiling can occur without happiness, happiness can occur without smiling (Krumhuber & Kappas, 2022).
The evolutionary history of a smile may have originated in fright. The ‘silent bared teeth display’ seen in a number of species certainly resembles a smile when performed by our close cousins, chimpanzees, who display it as a gesture of submission, appeasing more dominant members of a group. Human language may have had the next great evolutionary influence on our smile as smiling can make us sound friendly. Whilst this could be learned (Ohala, 1983; Pisan ski, Mora, et al., 2016), it could also be an evolved adaptation (Morton, 1977). By pulling the lip corners up and back, the zygomatic muscle shortens the mouth space in which sound waves can resonate during speech. The acoustic effect of smiling on human vocalisation is perceptible (Drahota et al., 2008; Ponsot et al., 2018), making the speaker sound like they’ve got a shorter vocal tract and, by association, and significantly, a smaller physique (Lindblom & Sundberg, 1971; Pisanski, Mora, et al., 2016). It could be that the effort to sound ‘smaller’ is perceived as a strategy to appear to be submissive, friendly or of no immediate threat (Fitch, 1997; Ohala, 1983).
The argument for a non-threatening origin of the smile is convincing, and our modern smile has many variations on this message (Ambadar et al., 2008; Ekman & Friesen, 1982; Keltner & Anderson, 2000; Tracy & Robins, 2008). Affiliation smiles (Martin et al., 2017) are common and encompass many forms. Yet not all smiles are done to achieve positive affect in the receiver; we also have smiles of superiority and dominance (Tracy & Robins, 2004), smiles that portray teasing (Haugh & Pillet Shore, 2018), and reveal feelings of schadenfreude (Cikara & Fiske, 2012).
As many, including Wood et al. (2022), have pointed out, smiles change the voice, but I would also argue that they change the ‘look’ of the face in another significant way – they portray the opposite of sadness. A sad face lengthens, the corners of the mouth turning downwards, but a smile pulls up a face’s centre of gravity, the cheeks rising and the corners of the mouth turning upwards. To smile is to attempt to show observers (and maybe even convince ourselves) that we are not feeling down. Instead, just as a smile lifts our face, our mood is seen to be uplifted. There is certainly a lot going on, and many a story, behind every smile.
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