The human smile is highly variable in both its form and the social contexts in which it is displayed. A social-functional account identifies three distinct smile expressions defined in terms of their effects on the perceiver: reward smiles reinforce desired behavior; affiliation smiles invite and maintain social bonds; and dominance smiles manage hierarchical relationships. Mathematical modeling uncovers the appearance of the smiles, and both human and Bayesian classifiers validate these distinctions. New findings link laughter to reward, affiliation, and dominance, and research suggests that these functions of smiles are recognized across cultures. Taken together, this evidence suggests that the smile can be productively investigated according to how it assists the smiler in meeting the challenges and opportunities inherent in human social living.

中文翻译：

---

微笑作为多用途社交信号

人类的微笑在形式和展示它的社会背景方面都非常多变。一个社交功能帐户根据它们对感知者的影响确定了三种不同的微笑表情：奖励微笑加强了期望的行为；隶属微笑邀请并维持社会纽带；和支配微笑管理等级关系。数学建模揭示了微笑的外观，人类和贝叶斯分类器都验证了这些区别。新发现将笑与奖励、归属感和支配地位联系起来，研究表明，微笑的这些功能在不同文化中都得到了认可。综上所述，这一证据表明，可以根据微笑如何帮助微笑者应对人类社会生活中固有的挑战和机遇，对微笑进行富有成效的研究。