Human language apparently has the structure and properties expected of a device produced by natural selection (Jackendoff 2002: chap. 6; Pinker and Jackendoff 2005). However, we continue to lack a clear theoretical explanation of how or why language evolved uniquely in the human lineage. Equivalently, we have not understood the circumstances under which language might have become adaptive in human ancestors but not in any other of the many thousands of large animal species. Though many theories of language evolution have been proposed in the ca. 150 years since Darwin, none has answered these questions convincingly nor born the fruit expected of a robust theory.
I briefly summarize here a body of new theoretical work which predicts that elite language should evolve uniquely in the humen lineage. These predictions arise simply, parsimoniously. Moreover, they account economically for all elite human communicative behaviors, not merely speech. This theory also suggests new perspectives on the structure of language and of the mind.
The concept of elite capabilities introduced above is vital. Various constraints impose adaptive trade-offs, resulting in elite execution of one task at the expense of merely serviceable (or negligible) capacity for another. For example, dolphins and horses are both mammals that can swim. Dolphins are elite swimmers but horses are not. All animals can (ostensibly; below) exchange information using symbolic, combinatorially generated and parsed gestures (manual/physical or vocal). Humans have elite skill at such exchanges, while no other animals (apparently) do.