Yerkish users are people who use a constructed language called Yerkish. This language was created in the 1970s by Dr. Duane Rumbaugh and is based on American Sign Language. It is used primarily by APES, such as chimpanzees, gorillas, and orangutans, to communicate with humans. The language consists of symbols that represent words and phrases, and is used to facilitate communication between humans and APES.