An ancient Greek philosopher once wrote that laughter is what makes us human—that it defines us as【T1】 1. Much more recent developments in biology and【T2】 2 suggest that not only humans but also【T3】 3 laugh: nonetheless, laughter is one of the most important aspects of human social life and【T4】 4. Laughter starts very soon after【T5】 5 —almost as soon as crying—and it serves many different【T6】 6 functions, from sharing our joy to intimidating and insulting other people. In many parts of the world, making other people laugh is considered a great gift, and【T7】 7 has always been a vital part of culture and art—perhaps precisely because of the complex, significant role of laughter in everyday life. 【T1】