As it turns out, there’s some serious science behind why babies laugh.
Dr. Caspar Addyman, University of London, said it was a topic “strangely neglected.”
He did possibly the most comprehensive survey on baby laughter thus far, with 1,400 interviews from around the world.
The reasoning is that since laughter comes when one understand a joke, understanding what babies laugh at could give insight to the infant mind.
Addyman found that babies first start to smile around six weeks, and 90 percent of babies laugh within the first two months.
Peekaboo and tickling are the top causes for baby laughter. Interestingly, he found that babies don’t laugh when other people fall over, but tend to laugh when they fall over themselves, because they respond mainly to physical sensation, and also tone of voice. It’s not funny when they see something disappear and suddenly appear, but funny faces an adult makes to accompany such tricks can make a baby laugh.
“Crying is a signal they want something to change, while smiling or laughter is the opposite—it says keep doing what you’re doing,” Addyman wrote.