The research program developed by Peter MacNeilage seeks to derive aspects of

phonological organization from fundamental physical properties of the speech

system, and from there to arrive at reasonable hypotheses about the evolution of

speech. Speech is the dominant medium for the transmission of natural human

language, and characterizing its organization is clearly very important for our

understanding of language as a whole. Speech is not the only medium available

to humans, however, and a comprehensive theory of the nature and evolution of

language has much to gain by investigating the form of language in the other

natural language modality: sign language, the focus of this chapter.