Task: Question Answering
Input (English): Context: Over time, the custom of kissing developed as a way for adults to express their love and affection for one another. The roots of this form of affection can be traced back to primitive times, when mothers fondled their children, much as mothers do today. Much later, in the sixth century, society apparently accepted the custom of kissing between adults as an expression of their affection. Not surprisingly, France first accepted kissing in courtship . There, figure dancing was popular, and each dance was sealed with a kiss. The custom of kissing swept from France through Europe to Russia, where Russian nobility loved to imitate the French. Eventually, the kiss was incorporated into marriage ceremonies, and today lip locks couples into sweet matrimony. The custom of kissing today, as well as in ancient times, serves to pay _ to another. Early Romans kissed each other on the mouth or on the eyes to greet one another in a manner they thought to be dignified. One Roman emperor even ranked a person's importance by the body part he was allowed to kiss. He allowed important nobles to kiss his lips, less important ones to kiss his hands, and the least important ones to kiss his feet. In Russia, the highest sign of recognition from the Crown meant a kiss from the Tsar himself. Today, natives of many African tribes pay homage to their Chief by kissing the ground over which he has walked. 
 Question: What's mainly talked about in the passage?
Output (English): the custom of kissing.