Ever wondered whether apes at the zoo are joking around with each other? It turns out they just might be. A recent study found that great apes—orangutans, chimpanzees, bonobos, and gorillas—tease each other playfully, suggesting that the cognitive tools humans use to develop a sense of humor may have evolutionary roots dating back at least 13 million years. Scientists observed great apes at zoos in San Diego and Leipzig, Germany, and saw all sorts of playful interactions, like poking and hitting. Teasing is a way for apes to learn social rules, hierarchies, and even sarcasm, they noted. And understanding how apes joke sheds light on their cognitive processes and offers insights into the origins of human behavior. As Maria Elide Vanutelli, a researcher at the University of Milano-Bicocca, told The Washington Post, “The study of these behaviors in animals provides an extremely innovative way of understanding how other species depict the world and what they find ‘amusing.’”