The Pivotal Role of Metaphor Since the function of language is to communicate thoughts and ideas, we need to understand how speakers succeed in this before asking how the system evolved. Language works through the complementary processes of ostension and inference, ostension being the production of cues to communicative intentions and inference being the interpretation of these cues. Viewed in this light, language takes its place as a particular type of ostensive-inferential communication. What distinguishes language from other such systems is that the cues provided by speakers are vastly more precise (Sperber and Wilson 1987). Far from being a rare and exotic deviation from the norm, figurative usage underlies all linguistic communication. It was once assumed that interpreting a metaphor involved literal translation, but nowadays, this is a minority view. To translate “John is a pig” into, say, “John is greedy” would be to lose much of the metaphor’s point. Often, there is no literal translation. Abstract concepts such as “time” in fact require metaphorical representation, as when we say “he has a great future in front of him” or “the summer is flying by” (Evans 2004). As figurative expressions become increasingly familiar, conversationalists resort to shortcuts, abbreviations, and conventionalizations in a complex process that, in principle, is entirely sufficient to explain how complex lexical and grammatical structures arise (Smith and Höfler 2014, 2016). The Language Evolution Conundrum The fictional status of metaphors poses an evolutionary conundrum. In the absence of very high levels of mutual trust and perceived common ground, we would expect listeners to reject all such fictions as attempts at deceit. Apes do not even attempt metaphor, insisting on hard-to-fake vocalizations that just cannot lie. While their manual gestures may be more flexible, there is nothing metaphorical about these. Despite their intelligence, apes not only do not talk—they will not even point things out for one another using their hands (Tomasello 2006). Tomasello (2008:5) comments that when a whimpering chimpanzee child is searching for her mother, it is almost certain that all of the other chimpanzees in the immediate area know this. But if some nearby female knows where the mother is, she will not tell the searching child, even though she is perfectly capable of extending her arm in a kind of pointing gesture. She will not tell the child because her communicative motives simply do not include informing others of things helpfully. Tomasello’s argument about the arm applies equally to an ape’s lips, tongue, soft palate, and mandible, all of which closely resemble the human speech articulators (Duchin 1990). Despite their sophisticated cognition, apes restrict these features to basic functions, such as chewing and breathing (MacNeilage 2008). While emitting a bark or cry, the tongue, for example, plays little or no role. “These expressive limitations,” notes Zuberbühler (2003:299), “seem to be rooted in at least two deficiencies: a lack of sophisticated control over the articulators in the supralaryngeal vocal tract and a remarkable shortcoming in social cognition.” Although references to ape shortcomings, deficiencies, and lack of control permeate the language-origins literature, we prefer Tomasello’s motivational account. Apes have many more capacities than they are normally inclined to use. Any hominin ancestor must have been able to control its tongue—otherwise, it would have been unable to taste, masticate, or safely swallow food. No ape or monkey has an inflexible tongue. When the animal needs to communicate a thought, however, it leaves the tongue out of it. It is this that needs to be explained. Signal evolution theory (Maynard Smith and Harper 2003) immediately suggests an explanation. Among the advantages of sound are that—unlike visible gesture—it carries over distances, goes around corners, and works in the dark. But insofar as a sound emanates from an invisible or distant source, the listener is deprived of contextual evidence of its reliability. Keeping vocalizations tied to bodily states may seem inexplicable to linguists, but it is a good way to give nonhuman listeners confidence in what they hear. “Who are you gonna believe, me or your own eyes?” joked Groucho Marx, reminding us that humans often acknowledge the same need. Mistrusting one another’s scheming, Machiavellian minds, primates ignore the alltoo-flexible tongue, preferring to rely on the evidence of their own eyes and ears. So here is the conundrum of language evolution. We need to explain how and why natural selection, in the human case, switched from quarantining the primate tongue—excluding it from all but a marginal communicative role—to developing and fine-tuning that same tongue’s role as the most important speech articulator of all. Since this development was biologically unprecedented, something quite specific and remarkable must have happened. The challenge is to narrow down what it was.
