While that fact is on slippery ground, with sources unable to come to a consensus on the exact number of muscles that are activated when we smile and frown, in the facial feedback hypothesis, we definitely have reason to smile.
While the weak version of facial feedback hypothesis suggests that physiological changes can only suppress or excite an existing emotion, the strong version suggests that such changes can create an emotion on their own.
While Darwin took into consideration the entire body, modern-day research seems to stress on the face, i.e., facial muscular activity.
Facial feedback hypothesis - Revolvy
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