Hockett's Design Features are a set of features that characterize human language and set it apart from animal communication. They were defined by linguist Charles F. Hockett in the 1960s. He called these characteristics the design features of language. Hockett originally believed there to be 13 design features. While primate communication utilizes the first 9 features, the final 4 features (displacement, productivity, cultural transmission, and duality) are reserved for humans.[citation needed] Hockett later added prevarication, reflexiveness, and learnability to the list as uniquely human characteristics. He asserted that even the most basic human languages possess these 16 features.