Before I get distracted by too much nit-picking, let me get to the summary paragraph: Thomas Scott-Phillips' book, Speaking Our Minds, contributes seriously to the study of language origins. First and foremost, it demands that pragmatics—the study of language in its social context—be included in the effort to understand language origins. What's more, it makes good on its case. Pragmatics has been underplayed and anybody who thinks about language origins should read and study the book. If the book were not so danged expensive, I would even urge you to buy a copy. (By the way, I've mentioned Scott-Phillips before—see Reality Blogging—and I remember him as a promising fellow at the Barcelona Evolang conference of 2008.)
The case for pragmatics rests on its special view of language as an ostensive-inferential communications system. Sorry, I'd like to use some other term, but that is the one used by the author and others, so we might as well hold our noses and roll with the bandwagon. You can understand it by imagining the archetypal scene in which Homo erectus A points toward a charging sabertooth tiger and a second erectus (B) looks on. What is going on here? First, A has something it wishes to communicate to B. Second, A shows its communicative desire by pointing. Then B has to realize that A is trying to signal something and not just holding out a finger for B's admiration. B then follows A's finger and sees the charging sabertooth. B now infers that A is signaling danger. Both A and B then shout out the erectus version of, "Feets, don't fail me now," and start running.
Even though all these details seem overthought and mildly absurd, that's what is going on in much human communication. On the ostensive side, a signaler has something to say and the desire to say it. On the inferential side, a receiver recognizes that the signaler is trying to be informative and determines just what the message is. We expert language users get through the ostensive-inference part pretty quickly and automatically, but I well recall an incident in which I rolled a ball past a one-year old. The toddler didn't see that the ball had rolled under something. He looked a bit perplexed. I pointed. The toddler looked at my finger for a moment, puzzled, and then did a visible double-take. He realized what I was doing and looked toward where I pointed. There was the ball. I had consciously combined an informative intent with a communicative intent, and the toddler had consciously inferred my intent and used it to learn something.
No other animal on earth, says Scott-Phillips, uses such a communication system. You will notice that this claim immediately redefines what the author wants to explain: "the real novelty is not in the origins of language per se, but rather in the origins of ostensive-inferential communication" [p. 153]. So, okay where did that type of communication come from and why are we the only species who uses it?
Before I go into Scott-Phillips' answer, let me get on with my nit picking. The author tends to claim he is presenting the whole ball of wax and he bases his claims on outrageous statements. For example, he says that there are only two types of communication possible: one "the code model" used by all other animals, and there is ostension, used by us. "Unless and until philosophical research is able to generate a third account of how communication can even exist, these are our only two options. This is, incidentally, not an empirical question, but a conceptual/philosophical one." 
Breathes there a reader with soul so dead who can meet this passage and not pause to hunt for another type of communication? It took me a very short time to think of a couple. Music was one. Certainly not all composers or musical performers have an informative intent; they needn't even be trying to move their audience in any kind of profound way. Entertainment is enough. Indeed, all of the arts, including novels, seem to press beyond the informative intent role without retreating back into the codes of the animal world.
Well, at first I grumbled, but then I thought I would let it pass. After all there is plenty to talk about in this book without getting stuck on these side issues. It turns out, however, that this kind of thing is exactly where Scott-Phillips' theory fails to satisfy. It claims to be the whole story when it is part of the story. It claims to have figured humans out when it doesn't even notice that we all have sides that defy efficiency and information.
But once the reader notices these flaws, they can be put aside. The author waves away objections with a swatting hand that fails to convince, but so what? Nobody in the origins-of-language game has got the whole story, and at least ostensive-inference is not so patently not-the-whole as recursive syntax. So let me list 5 things that Scott-Phillips contributes that are truly grand:
- Pre-fluency: We are fluent communicators, but back when we were new at the ostensive-inferential game we were probably awkward communicators. By stressing the non-linguistic side of human communications, Scott-Phillips is able to evoke the time when pointing and shrieking was the best we could do. Bickerton also covers this material (see Bickerton: Round Two) but I think Scott-Phillips does a livelier job of it.
- Humpty-Dumpty was right: As many linguists do, Scott-Phillips cites the passage in Alice in Wonderland where Humpty Dumpty tells Alice that when he uses a word it means "just what I choose it to mean." More unusual is the conclusion that Humpty-Dumpty is "right. You can make words mean many different things. Indeed, you can make them mean pretty much anything at all, if you have the right context."  This attitude reflects one of the book's strongest virtues. It presents language as a kind of Swiss Army knife of communication, not a fixed set of computational rules. The existence of poets is always a mystery for devotees of Universal Grammar, but not here.
- The value of ambiguity: Chomsky frets a great deal about ambiguities as a weakness of language, but Scott-Phillips replies "that speakers who wish to be efficient in what they do should be ambiguous, to the extent that this ambiguity can be resolved by context."  I don't think this observation will come as a revelation to any regulars on this blog, but it is part and parcel of Scott-Phillips' ostensive approach and is the kind of commonsense conclusion that his work supports rather than denies.
- Why apes don't have language: There is a simple, selfish gene theory that explains why most animals don't have language, but Scott-Phillips offers a different one, "If we accept that great apes do not communicate ostensively, then we have a ready-made explanation for why they don't have languages."  There is a brazenness to this claim that I deeply enjoy. It's like listening to the patter of a first-rate magician. A few sentences before, the author had been discussing the question of whether apes do communicate ostensively and he asked, "If [apes do use ostensive communication] then why don't apes also communicate linguistically in even a basic way?" It is a beautiful circle: apes don't have language because they don't use ostensive communication and we know they don't use ostensive communication because they don't have language. This circle did not arise because the author is illogical. It reflects his hurry to claim the whole story for his deeply under-respected branch of linguistics. I stand persuaded that ostensive-inference must be included in the consideration of language origins, but it does not put an end to all other factors. In particular, we need to understand how we got past the selfish-gene problem that does away with sharing advantageous information.
- Cultural attractors: Back in Barcelona, Scott-Phillips shared a prize with Olga Feher for best presentation by a student. Feher's work found that if you taught a zebra finch some non-finch song, the next generation would learn the non-finch song but over several generations the finches come back to singing the normal zebra finch song. Scott-Phillips cites this work and nicely clarifies its mystery, calling it an example of "cultural attraction." We have seen hints of this notion before on this blog. Particularly important was the Dediu and Ladd paper (see Was the First Language Tonal?) which provided evidence that the genetic structure of a population can lead to the appearance or disappearance of a linguistic feature. Thus, if I took a population of English speakers with the tonal gene and isolated them for N generations, we could expect their version of English to develop some tonal qualities. That change would arise from an "attraction," that is a tendency to move in a certain direction. This concept was also useful in the Evans and Levinson paper (see Is Anything Universal in Language?) which rejected the idea of a Universal Grammar in the Chomskyan sense and spoke instead of attractors, cognitive and genetic tendencies that led languages to acquire certain general similarities even while becoming very different in other ways. But while the Feher, Dediu and Ladd, and Evans and Levinson papers have all stayed in my head, the term "attractor" did not. Scott-Phillips recovers the term and explores it at, for him, some length. So now we can name the alternative to Chomsky's Universal Grammar: cultural attraction. I can already see many uses for this notion from ethics, to religion, to literary criticism, to history.
I'm sure that anyone interested in this blog's contents will find plenty of engaging material in Scott-Phillips' book. Tell your local library to get a copy.
Oh, yeah. I said I would the answer to the question where did that type of communication come from and why are we the only species who uses it? The author says "of all primate species, only we began to live in social groups so large and complex that there was natural selection for the sort of advanced social cognition … that made ostensive-inferential communication, and, hence, language possible."  What were the pressures that led to such unwieldy group sizes? Why haven't other primate groups been subject to similar pressures? What indeed is the evidence that Homo something-or-other was living in populations larger than a large baboon troop? I dunno; ask Thom.