Watching language grow

Because sign languages are processed by eye and hand rather than by ear and mouth, we might expect them to be structured differently from spoken languages. However, they are not. Sign languages are characterized by the same hierarchy of linguistic structures [syntax (1), morphology (2), and phonology (3)], and thus draw on the same human abilities as spoken languages. Moreover, children exposed to sign language from birth acquire that language as naturally as hearing children acquire the spoken language to which they are exposed, achieving major milestones at approximately the same ages (4, 5).

However, the manual modality makes sign languages unique in at least one respect. It is relatively easy to use the manual modality to invent representational forms that can be immediately understood by naïve observers (e.g., indexical pointing gestures or iconic miming gestures). As a result, communication systems can be invented on the spot in the manual modality, which means that sign systems have the potential to provide a window onto the process of language creation. Indeed, deaf individuals have often found themselves in situations where they needed to create a language de novo.

One such situation is described by Sandler et al. in this issue of PNAS (6). A community, now in its seventh generation and containing 3,500 members, was founded 200 years ago in Israel by the Al-Sayyid Bedouins. Within the last three generations, 150 deaf individuals were born into this community, all descended from two of the founders' five sons. Al-Sayyid Bedouin Sign …