Abrupt grammatical reorganization of an emergent sign language

This study traces the development of discrete, combinatorial structure in Zinacantec Family Homesign (‘Z Sign’), a sign language developed since the 1970s by several deaf siblings in Mexico (Haviland 2020b), focusing on the expression of motion. The results reveal that the first signer, who generated a homesign system without access to language models, represents motion events holistically. Later-born signers, who acquired this homesign system from infancy, distribute the components of motion events over sequences of discrete signs. Furthermore, later-born signers exhibit greater regularity of form-meaning mappings and increased articulatory efficiency. Importantly, these changes occur abruptly between the first- and second-born signers, rather than incrementally across signers. This study extends previous findings for Nicaraguan Sign Language (Senghas et al. 2004) to a social group of a much smaller scale, suggesting that the parallel processes of cultural transmission and language acquisition drive language emergence, regardless of community size.