Primatologist Signe Preuschoft traces the smile back over 30 million years of evolution to a "fear grin" stem…

Primatologist Signe Preuschoft traces the smile back over 30 million years of evolution to a "fear grin" stemming from monkeys and apes, who often used barely clenched teeth to portray to predators that they were harmless\[2] or to signal submission to more dominant group members.