Recursion: What is it, who has it, and how did it evolve?

Recursion is a topic of considerable controversy in linguistics, which stems from its varying definitions and its key features, such as its universality, uniqueness to human language, and evolution. Currently, there appear to be at least two common senses of recursion: (1) embeddedness of phrases within other phrases, which entails keeping track of long-distance dependencies among phrases and (2) the specification of the computed output string itself, including meta-recursion, where recursion is both the recipe for an utterance and the overarching process that creates and executes the recipes. There are also at least two evolutionary scenarios for the adaptive value of recursion in human language. The gradualist position posits precursors, such as animal communication and protolanguages, and holds that the selective purpose of recursion was for communication. The saltationist position assumes no gradual development of recursion and posits that it evolved for reasons other than communication. In the latter view, some heritable event associated with a cognitive prerequisite of language, such as Theory of Mind or working memory capacity, allowed recursive utterances. Evolutionary adaptive reasons for recursive thoughts were also proffered, including diplomatic speech, perlocutionary acts, and prospective cognitions.