When a group of people laugh, people will look at the person they feel closest to in that group due to interest indicators per supporting research by Norman P. Li et.al. in 2009.
"Humor plays a large role in our everyday lives and is pervasive across all cultures. We seek and rapidly notice humor whether we are going to the movies, interacting with a stranger or a friend, or looking for a potential romantic partner." The interest indicator model suggests that humor can function as a key tool for both facilitating and maintaining social relationships within a group of people. The interest indicator model also proposes that humor is inherently different from intelligent conversation and serves an important function beyond courtship or intrasexual competition. Humor also functions to indicate interest in social relationships to initiate new relationships and to monitor existing ones. Co-evolution of laughter and language, humor initiation and appreciation may have developed as a way for individuals to initiate and maintain different social relationships.
For ongoing relationships, the relative costs and benefits underlying the relationships may change over time for each person, hence the need for ongoing assessment of the relationship. In this process of establishing new relationships and assessing existing ones,
humor may allow individuals to implicitly communicate their interest and gauge the corresponding level of agreement from others. That is, by initiating humor, a person may be implicitly suggesting interest in a new or already established relationship. To the extent that the audience is also interested, they will respond positively.
Results of the 2009 paper 'An Evolutionary Perspective on Humor: Sexual Selection or Interest Indication?' across three studies supported predictions derived from this model. In Study 1, both sexes reported being more likely to initiate humor and to laugh in response to humor when they were initially attracted versus not attracted to a potential mate. In Study 2, experimental evidence was found for the view that initial attraction and interest in a potential relationship predict judgments of humor. In Study 3, people viewed male female pairs interacting in speed dating sessions and indicated that they recognized the relationship dynamics of humor predicted by the interest indicator model. This suggests that humor can ultimately function as a strategy to initiate and monitor social relationships.
The reasons why a more indirect approach of humor such as describing interest overtly asking for agreement might be advantageous and adaptive than a direct approach of implicitly conveying relationship interest is as follows:
"There may not be enough information to make an outright commitment to or rejection of a relationship. For instance, when individuals initially meet, it may be unclear to either side whether the other person would make a good romantic partner, friend, or coalitional ally. Similarly, partnered individuals who are losing interest in each other may not be ready to abruptly end a relationship. As such, humor may allow individuals to indicate the direction of their interest and to build (or deconstruct) relationships incrementally."
"Since an indication of interest conveys much less information than an evaluation of a full relationship, the costs of being rejected for an indication should be lower. Such costs include future possibilities for the relationship and one’s reputation. Humor initiation may yield an indication of interest without incurring such consequences."
"By using humor, one can gauge the strength of a potential or existing relationship without revealing his or her ultimate motives, which may extend beyond the establishment of a relationship. For example, if one needs to confide in and elicit the assistance of someone concerning an important matter, he or she may wish to first assess the strength of various relationships before choosing who."