Human language evolution: clustering of fifteen language comprehension abilities in 55558 individuals suggests three-step-wise language comprehension acquisition

There is an opposition between saltationist and gradualist hypotheses of human language comprehension evolution. The saltationist hypothesis argues for an abrupt step-like transition from non-recursive to recursive language sometime around 100,000 years ago. The gradualist scenario conjectures a much slower acquisition of grammatical and syntactic abilities over several million years. The former hypothesis expects a uniquely-human neurological mechanism made possible by a single mutation that resulted in simultaneous acquisition of a whole range of uniquely-human linguistic abilities, while the latter believes that many different mutations enabled various uniquely human neurological mechanisms that underlie human linguistic abilities. Studying co-acquisition of various linguistic abilities in modern humans can help resolve the two competing scenarios. The saltationist single-neurological-mechanism hypothesis predicts a two-cluster solution (one cluster of individuals who acquired that mechanism and another cluster of individuals who did not), while the gradualist scenario predicts the solution with many smaller clusters. Accordingly, we investigated co-acquisition of fifteen language comprehension abilities in 55,558 individuals using data-driven clustering analysis. Multiple clustering methods resulted in a robust three-cluster solution suggesting a three-step-wise language comprehension acquisition.