Evolutionary Explanations of Humor

How Do We Know That Humor Evolved?

Researchers have been studying the evolutionary adaptations behind many human attributes and behaviors for decades. Biologists have identified several key features that indicate whether a certain trait has an evolutionary basis. This includes universality of the trait, early developmental onset, and presence in other species, especially our closest relatives, other primates. Let us examine how humor fits these general criteria for adaptation.

First, humor is a universal human phenomenon, enjoyed on a daily basis in both tribal and industrialized societies. Mechanisms such as surprise and incongruity in nonserious social interactions are ubiquitous and seem to elicit mirth from people everywhere in the world. Second, smiling and laughter have been documented not only in all human societies, but also in other species, especially apes and primates. There are even studies that suggest that rats can laugh.

In primates, there seem to be two distinct facial expressions that are homologous to human smiles and laughter. The silent bared teeth display is equivalent to the human smile and appears as a sign of submissive appeasement that leads to an inhibition of aggression in the receiver, while the relaxed open mouth display, homologous to human laughter, appears in social play as a sign of enjoyment. While these two displays are quite distinct in apes and emerge only in specific situations, they seem to converge in humans. Humans smile and laugh in response to the same stimuli, and the smile or laughter reflects the magnitude of joy, not the nature of the interaction as with other apes.

Third, smile and laughter develop around the same time, early and spontaneously, in every culture in the world. Babies who are just born smile reflexively and start laughing vocally at around 2 to 4 months of age. These smiles and laughs develop before language and have stereotypical expression and sounds that are easily recognizable by every culture in the world. If we record laughter or take pictures of people smiling and laughing in one society, and then present them to members of another society, they will easily recognize them and attribute the correct emotion to them. Even babies who are born blind or deaf smile and laugh involuntary, not needing to see or hear others smile and laugh, lending support to the notion that smile and laughter are not restricted by culture.

Evolutionary Mechanisms That Can Explain Humor

Several evolutionary theories have been offered over the years to explain the adaptive function of humor. These theories vary in scope and illuminate different facets of humor and laughter. While there is no consensus among researchers on what evolutionary theory best explicates humor, all theories fall under one of two evolutionary mechanisms: natural selection and sexual selection. Natural selection is the process by which humans and animals inherit biological traits that help them to survive and reproduce. If humor was shaped via natural selection, then we can expect that it will contribute to one's health, directly or indirectly (for example, by relieving the tension in a fearful situation). Explanations that are based on sexual selection theory emphasize the importance that humor plays in finding a mate [Page 220] and how it can enhance the chances of reproducing successfully. Let us examine some of these theories in more detail.

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