Do animals have a sense of humor?

Right now, in a high-security research lab at Northwestern University’s Falk Center for Molecular Therapeutics, scientists are tickling rats. Their goal? To develop a pharmaceutical-grade happiness pill. But their efforts might also produce some of the best evidence yet that humor isn’t something experienced exclusively by human beings.

Scientists believe human laughter evolved from the distinctive panting emitted by our great-ape relatives during rough and tumble play; that panting functions as a signal that the play is all in good fun and nobody’s about to tear anybody else’s throat out. In a clever bit of scientific detective work, psychologist Marina Davila-Ross of the University of Portsmouth in the United Kingdom analyzed digital recordings of tickle-induced panting from chimps, bonobos, gorillas, and orangutans, as well as human laughter, and found the vocal similarities between the species matched their evolutionary relationships. Chimps and bonobos, our closest relatives, boast the most laughter-like kind of panting, while the noises of gorillas, further down our family tree, sound less like laughing. And orangutans, our truly distant cousins, pant in a most primitive way.