Three clusters of grammatical abilities in individuals with language deficits “split” the universal grammar hypothesis

Abstract In this study we assessed 15 language comprehension abilities in 55,558 individuals with language deficits 4 to 22 years of age using parent-generated reports. Data-driven cluster analysis identified three distinct clusters of co-expressed abilities. The first cluster, termed “command language,” included knowing the name, responding to ‘No’ or ‘Stop’, responding to praise, and following simple commands. The second cluster, termed “modifier language,” included understanding color and size modifiers, several modifiers in a sentence, size superlatives, and numbers. The third cluster, termed the “prepositional language,” included understanding of spatial prepositions, verb tenses, flexible syntax, possessive pronouns, explanations about people and situations, simple stories, and elaborate fairy tales. Independently, we performed data-driven cluster analysis of participants. 19.8% of participants were limited to command language phenotype; 58% of participants were limited to modifier language phenotype; 22.2% of participants were clustered to the most-advanced prepositional phenotype. All neurotypical participants were clustered to the prepositional phenotype. While the Universal Grammar hypothesis attempts to preach a dichotomy between the presence of grammatical abilities in humans and their absence in animals, this study shows that there are additional distinct language comprehension phenotypes that require an explanation.