Download One explanation to rule them all?

The field of language evolution, it seems to me, is a microcosm of the evolutionary behavioral
sciences more generally, in the following sense: you can maintain more or less any position you
want, even in the face of data. Is there a Universal Grammar? Some are convinced there is and
others are equally positive there isn’t, with subjective probabilities for the two hypotheses hovering
in the high nineties and low single digits, respectively, in the opposing camps. Is spoken language
evolutionarily old, or relatively recent? Take your pick. Are there language-specific cognitive
adaptations, or not? It depends on your postal code.
Amidst this free-for-all, many have tried their hand at finding the holy grail of language evolution:
the single unique feature from which all the rest of language’s notorious complexity follows, the one
explanatory ring to rule them all. Examples include Michael Tomasello’s candidate, shared
intentionality, and Hauser, Chomsky, and Fitch’s recursion. With Speaking Our Minds (SOM), Thom
Scott-Phillips introduces and defends his own candidate for what makes human language special:
ostensive-inferential communication, which is in turn made possible by recursive mindreading. SOM
mounts an impressive theoretical argument, and along the way makes a strong plea for the
importance of bringing pragmatics to the fore in thinking about language evolution. I think the
praise that the book has received is well-deserved, and I can’t imagine any serious scholar in the
field of language evolution won’t feel compelled to read it and to engage with its arguments.
My comments about the book can be arranged into two basic categories, in descending order of
positivity. First and most importantly, I could not be more enthusiastic about SOM’s emphasis on the
importance of theory of mind and pragmatics in understanding language evolution. I agree that
theory of mind is likely to have played a much larger role than anyone has yet recognized in enabling
not only linguistic communication, but cultural transmission and cooperation more generally. To me
the importance of mindreading in enabling and stabilizing many forms of human sociality has been
criminally underexplored, and I’m not sure why. One possible explanation is Tooby and Cosmides’
notion of “instinct blindness:” mindreading underlies so much of everyday social interaction, and we
do it so effortlessly, that we scarcely notice its operation or feel it necessary to invoke it in
explaining communication and cognition. Whatever the reason, we are still largely in the dark about
how important various forms of mindreading might be in solving the social adaptive problems that
must be solved to make human communication and cooperation stable. Thom and I are entirely on
the same page about this.
My second category of comment takes a more skeptical turn. While I find Thom’s account of the
uniqueness of human language plausible, I am by no means convinced that he has identified, in
recursive mindreading and ostensive communication, the prime causal mover that gave rise to the
rest of human linguistic complexity. Because I take a broad view of what mindreading is—and I
believe that basic components like intention-reading are phylogenetically widespread—I assume that
mindreading, broadly speaking, far predates language. Moreover, I agree that some fairly
sophisticated mindreading abilities such as belief tracking had to be in place before important
aspects of human language, such as implicature, evolved. However, I am not yet convinced that
multi-level recursive mindreading is the main element that gave rise to the rest of linguistic
complexity. It’s certainly possible, but I don’t think the evidence is yet sufficient to call the game for
recursive mindreading. Indeed, I think there are several links in the causal story offered in SOM
that, while plausible, still remain to be verified. Thus, while I think the book’s focus on the
importance of mindreading and pragmatics in language evolution is spot-on, I think it takes a victory
lap too soon in declaring the major mysteries of language evolution solved.
This is true for both theoretical and empirical reasons. Empirically, I think we just don’t have enough
evidence to say for sure whether many of the book’s key claims are true. And theoretically, I think
there remain some mysteries even in some of the more basic mechanisms that Thom calls “well
understood.” In the epilogue at the end of the book titled “The Big Questions Answered,” Thom’s
ninth and final question and answer are:
Q: Coherence: Does the proposed account depend only on well-understood evolutionary mechanisms,
or is it more speculative?
A: My proposals depend on well-understood evolutionary mechanisms alone.
I suppose one man’s understanding can be another man’s confusion, and I might be the confused
one here. But as SOM points out, linguistic communication depends on solutions to deep problems of
cooperation—in particular, the problem of what makes linguistic communication honest—and I don’t
think the underlying mechanisms are well understood at all. Thom opts for reputation as the
stabilizing mechanism, and it’s true that there exist game theoretic models in which reputational
costs stabilize signal honesty. In that sense, the mechanisms in those models may be “well
understood,” but I don’t think that’s equivalent to saying that the mechanisms that actually stabilize
cooperative communication in human language are well understood. Indeed, problems of stability in
linguistic communication are a subset of problems of large-scale cooperation more generally. While
it’s clear that these problems have been at least partly solved in human cooperation—for example, I
can engage in successful communication with a stranger I’ll never meet again—it’s not at all clear
how they have been. Indeed, the problem I attributed to the field of language evolution, i.e., that you
can believe more or less anything you like, seems to apply just as much if not more so to the field of
the evolution of cooperation. Claims of “X” and “not X” coexist quite stably in this literature, as seen
in debates over group selection, strong reciprocity, and the like. So, I don’t think we’ll be ready
anytime soon to check the “Question Answered” box for what stabilizes large-scale cooperation.
Then there is the claim that what makes human linguistic communication special is ostensiveinferential communication, which in turn depends on recursive mindreading. Here again, while I
think there is a plausible causal story, I’d like to see both better theoretical support in the form of
evolutionary models, and much better empirical support from work in humans and other animals,
including evidence from everyday linguistic communication outside the lab. It’s clear, from work by
Thom and others, that humans can do recursive mindreading. SOM also offers some tentative
evidence that only humans can do this, and that only humans have ostensive-referential
communication. However, showing that humans have these abilities and that chimps do not is not
the same as showing that these abilities causally enabled the evolution of human linguistic
complexity. Indeed, that is difficult to show, because recursive mindreading and ostensive
communication are offered as the ultimate causes of human linguistic complexity, and causation is
notoriously difficult and perhaps impossible to show using the comparative method. This is
especially true when there is only one taxon that shows all of the traits in question (us). And these
aren’t the only cognitive traits that are uniquely derived in us; there have been changes in brain
size, executive control, planning, tool use, social learning, social complexity, and more. Which factor
is causal, if any? Moreover, while recursive mindreading of many levels can be shown in the lab, we
don’t yet know how much everyday speech depends on many-level recursive embeddings of mental
state inference, nor how much recursive mindreading is actually predicted by the theory. What
amount, or lack thereof, would falsify the theory? Or is the mere demonstration that humans can do
it enough to call the question settled? Because this is a theory that depends on a complex causal
cascade, many of the steps of which have not yet been fully theoretically elaborated or empirically
demonstrated, I think we have a long way to go before declaring all of the Big Questions answered.
To me, though, that’s no reason not to take seriously SOM’s argument for the likely importance of
mindreading in language evolution, and to do so without considering the Big Questions of language
evolution settled. Indeed, in my view, we’re better off proceeding without declaring a winner,
because I doubt that there is one true explanatory ring to find. Instead, my hunch is that
mindreading has been just one factor among many in enabling the gene-culture coevolutionary
pathway leading to the current state of human linguistic complexity. If that’s so, the answers to the
Big Questions will come not in the form of simple propositions involving easily stated concepts such
as “ostensive communication,” but rather, a messy causal graph including many directed edges that
we have yet to discover or name. Still, that’s no reason not to turn our attention right now to the
importance of mindreading in language evolution and cultural evolution more generally. I hope that
Speaking Our Minds convinces others, including researchers and granting agencies, that this is a
quest well worth pursuing.