They'll smile appropriately, making an important point that smiling is not learned by looking at other people's faces.

他们会适当地微笑，说明微笑不是学习的,通过观察其他人的面部表情。

耶鲁公开课 - 心理学导论课程节选

Rather, people smile when they wish to communicate happiness and we know that from several studies.

相反，人们微笑是渴望能开心地交流,从一些研究中，我们知道。

耶鲁公开课 - 心理学导论课程节选