Speech, verbally mediated consciousness, and culture most evidently differentiate people from animals. Moreover, verbal communication has historically been viewed as a human attribute. Yet, the biological precursors to verbal communication exist in animal communication: obvious links have been found between human and animal nonverbal vocal communication. Knowledge of these links contribute to our understanding of three major theoretical and clinical issues: the evolution of vocal communication; the process of speech acquisition during infancy; and the pathways of disorders in communicative...