Before they speak or crawl or walk or achieve many of the other amazing developmental milestones in the first year of life, babies laugh. This simple act makes its debut around the fourth month of life, ushering in a host of social and cognitive opportunities for the infant. Yet despite the universality of this humble response and its remarkable early appearance, infant laughter has not been taken seriously. At least, not until recently. In the past decade, researchers have started to examine what infant laughter can reveal about the youngest minds, whether infants truly understand funniness, and if so, how.
Prompted by observations of infant laughter made by none other than Charles Darwin himself, modern psychologists have begun to ask whether infant laughter has a purpose or can reveal something about infants’ understanding of the world.
Darwin speculated that laughter, like other universal emotional expressions, serves an important communicative function, which explains why nature preserved and prioritised it. Two key pieces of evidence support Darwin’s hunch. First, according to the psychologist Jaak Panksepp of Bowling Green State University in Ohio, laughter is not uniquely human. Its acoustic, rhythmic, and facial precursors appear in other mammals, particularly in juveniles while they are at play, pointing to the role of evolution in human laughter.