Have you been tickled recently, or have you tickled?

Apparently, this intimate and usually fun interaction between humans–especially between parents and small children–is not an exclusively human trait. According to a new study, apes have been tickling each other and laughing for millions of years. Why? It’s not clear, although the survival of tickling for so long suggests that apes and humans have prospered and reproduced more than those who did not.

Here is a description of the study from a blog entry by 23andMe’s ErinC:

Researchers from the University of Hannover in Germany recorded the tickle-induced vocalizations from three human infants and 21 infant and juvenile orangutans, gorillas, chimpanzees and bonobos and analyzed this acoustic data to find similarities and differences among the five species. Their results, published online today in the journal Current Biology, show that not only are the hoots, hollers and snorts of the great apes really laughter, but the evolutionary relationships between the sounds match up with the known evolutionary relationships between the species based on genetics.

“At a minimum, one can conclude that it is appropriate to consider ‘laughter’ to be a cross-species phenomenon, and that it is therefore not anthropomorphic to use this term for tickling-induced vocalizations produced by the great apes,” the authors write.

But the researchers’ findings also indicate something more profound: rather than being a uniquely human invention, tickle-induced chuckles can be traced back 10 to 16 million years to our last common ancestor with the great apes. Analysis of the chortles of a lesser ape, the siamang, suggests that laughter may be even older.

Despite all the similarities the researchers found between humans and the great apes, the fact remains that human giggles are distinct: we mostly laugh while exhaling, and our vocal cords vibrate to make the “ha ha ha” sounds, while ape snickers are more of the in-and-out panting variety.