The study of flexibility in communication systems in a wide variety of animals is offering new perspectives on the special forces that may have favored the evolution of language, with its omnipresent and seemingly unlimited flexibility. A variety of birds, marine mammals, New World monkeys, and even certain invertebrates show notable capabilities to break free from the fixed signaling patterns that have been so much the focus of description in classical ethology. A useful summary of the selection forces that favor steps toward contextual flexibility can now be provided, a summary that places in perspective speculations about the forces that may have guided hominid evolution toward spoken language. Research in human infant vocal development also provides invaluable clues about the first steps of vocal communication that may have been taken by ancient hominids as they became differentiated from the primate background. In particular, human infants, during the first half-year of life, develop capabilities to produce vocalizations with a remarkable degree of contextual flexibility, apparently surpassing all the other primates and perhaps all other mammals. Since spoken language requires vocal contextual flexibility in all its aspects and functions, it appears that an extremely early step in hominid evolution, establishing a necessary foundation for later evolution of language, was the emergence of contextually flexible vocalization. Philosophical work on communication and its origins along with modeling and simulation have vastly increased our view of possible sources and routes in the emergence of language. An important focus for such work is the formal conditions under which systems of communication can break free from the bonds of fixed signaling, the primary mode of vocal communication in the primates. Developing an understanding of these formal conditions is crucial in understanding the evolution of language.