A real smile involves more muscles than a fake one, including the orbicularis oculi and pars orbitalis. A genuine smile is known as a Duchenne smile and is symmetrical, lasts up to five seconds, and causes the tips of the eyebrows to droop slightly. Smiling is universal and may have evolved from an expression of fear. Being able to spot a fake smile may confer an evolutionary advantage.
A fake smile actually uses different muscles than a real smile. Because a real smile is involuntary and a fake one is intentional, different parts of the brain control which muscles are used for each. The muscle responsible for drawing the corners of the mouth outward, the zygomaticus major, is active in both types, but additional muscles are involved in true smiles. When a person sincerely smiles, the orbicularis oculi and pars orbitalis contract in addition to the zygomaticus major, causing the cheeks to lift and the skin around the eyes to fold. A genuine smile is also known as a Duchenne smile, as French neurologist Guillaume Duchenne discovered the distinction between the muscles used in fake and real smiles in the 19th century.
One of the best ways to spot a fake smile is to look at the tips of the eyebrows, which droop slightly when a smile is real. Also, in a real smile, the fold of skin between the brow and eyelid moves downward. False smiles are less likely to be symmetrical than a real smile, as voluntary control of the zygomatic major is not always perfect. A genuine smile lasts up to five seconds, while a fake one can last much longer. While a fake smile can be very convincing and can even make your eyes roll a bit, with practice many people can distinguish a genuine Duchenne smile from a deliberate one.
Smiles that express happiness aren’t just superficial; people in every culture smile alike, and even people born blind smile involuntarily when they’re happy. Many biologists think that the smile arose from an expression of fear, such as a grimace, as some primates display their teeth slightly clenched to indicate that they are harmless to potential predators. Being able to spot a fake smile may also be an evolutionary adaptation, as determining whether or not others are truly cooperating and bonding with you may confer an evolutionary advantage.
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