Terrence Deacon, Ph.D. - The Co-evolution of Language and the Brain

Dr. Terrence Deacon:  I began the study of language and the brain mostly because it is the most fascinating subject around with the biggest problems. Of course to look at its evolution is sort of the real challenge, the real golden egg one searches for. The challenge for me as a young student was that there was really no place I could go where people were actually studying brains to understand how they evolved. There were a lot of people studying how big brains were and things like that but there was not a lot of neuroscience when I began as a young student directed in that particular enterprise. That became a challenge for me and I did all that I could to study both the linguistic side of things, the communication side, but also the neuro-anatomical side of these questions. 

It turns out that, of course, the study of brains and the study of language can’t be done in one field. It really requires that you sort of dabble in many fields and become perhaps a master of none. The danger, of course, is that you get a superficial picture. But you get a superficial picture if you’re just in one area as well. I have tried throughout my career to sort of walk that middle ground and ask the question, “What do I need to know to answer these questions?” Most of my work was in the neurosciences. I began in the earlyeighties by trying to adapt some of the new technologies for tracing connections in brains that I thought might be a way to go at the question.  

In fact, some of my early work traced the connections in monkey brains that corresponded to the language connections in human brains.  That’s what really got me on my path, partly because a surprise came of that work. We suspected that the areas in human brains where we find language connections would be quite different in monkey brains. The surprise was that, as far as we could tell, the plan was the same plan. The way these areas were connected, even areas that we identified as language areas, or the correspondent areas in monkeys, had the same kinds of connections. It was a baffling finding and, in fact, the more we got new data about humans brains the more we found that the data we had picked up on monkey brains, and how they were organized, actually predicted the connections and the functionality of these language areas and how they were distributed. 

So, a brain that didn’t do anything like human brains do in terms of communication and vocalization and so on, nevertheless seemed to have the same organization. It was one of the first big turning points, I think, in my work in realizing that somehow we would have to explain how the same kind of computer, (I think computer is a bad metaphor but it’s the one we have), how the same kind of device was running a very different kind of software, so to speak. How it could be, how the tweaks in that system might have worked. To study that I went off in a number of directions, more mapping of brain areas in primates trying to understand their links to humans, but also much more comparative work, and also developmental work. I spent a good deal of the last decade studying how brains develop because, of course, brains don’t evolve from adult stage to adult stage. What happens is embryology changes over the course of evolution and that changes the resultant.  That area also has been full of surprises as we pursued it forward in these last couple of decades. 

Dr. Terrence Deacon:  Most surprisingly is that brains are not, it's hard to say this but, brains are not designed the way we would design any machine. They are not built the way we would build a machine. We don’t take the parts and put them together to build a whole.  In fact, what happens is just the other way around. The whole starts out, it’s just undifferentiated. The parts aren’t distinguished from each other and they become more and more different from each other. The system becomes more and more complicated. The problem is the process is very indirect. 

It is not like building something from a plan. It’s a very indirect process. It became very clear that this process is very much what we would call today, self organization. A lot of the information that goes into building brains is not actually there in the genes. It’s sort of cooked up or whipped up on the fly as brains develop. So, if one is to explain how a very complicated organ like the brain actually evolved, changed it’s function to be able to do something like language, one has to understand it through this very complicated prism of self organization and a kind of mini-evolution process that goes on as brains develop in which cells essentially compete with each other for nutrients. Some of them persist and some of them don’t. Some lineages go on to produce vast structures in the brain.  Other lineages get eliminated as we develop, in some ways just like a selection process in evolution. 

Like evolution, it’s a way of creating information on the fly - a sort of sampling the world around you, in this case the body as well as the external world and adjusting yourself to it. In some ways the brain has that character, too. The complication of all of this has made me realize that the problem of language is a problem that’s not going to be ultimately solved by a kind of engineering model, by a kind of reverse engineering. We are going to have to think, in a sense, like biology thinks, like embryology works in this kind of self organizing, self evolving-like logic to get back at what actually causes things to occur and develop in complex ways. 

I think this is the case with language itself. As it’s passed from generation to generation it has a kind of self organizing and evolution-like character to it. That is also part of where the structure comes from, where it picks it up on the fly, so to speak. We have to work that into our stories. That is really the impetus for the book I wrote. The Symbolic Species captures the essence of that idea in its subtitle, The Co-evolution of Language in the Brain. Ultimately, my argument was that language itself was part of the process that was responsible for the evolution of the brain. I mean that in the following sense.

Imagine the evolution of beavers. Beavers are aquatic animals today but they are aquatic because of what beavers in the past have done. That is, beavers have created their own world to some extent. They’ve created an aquatic world by building dams and blocking up streams and turning them into small lakes. Beavers’ bodies have evolved in adaptation to the world that beavers created. It’s a kind of complex ratcheting effect in which what you do changes the environment that produces the selection on your body.

I think language is, in a sense, our beaver dam. Language has changed the environments in which brains have evolved. That changes the picture radically because now one can look at the brain, so to speak, with an inside out perspective of the problem and ask the question, “What’s different about human brains and how might that difference tell us something about the forces that shaped it?” If those forces include language then the brain itself is a wonderful signature, a wonderful trace for the forces that helped it evolve in this complicated interaction. The title, The Symbolic Species, captures this notion that we are a species that in part has been shaped by symbols, in part shaped by what we do. Therefore, our brain is going to be very different in some regards than other species' brains in ways that are uniquely human.  

David Boulton: There are so many things to talk about. I’m both interested in the general work that you’re doing and how I can relate that to the story that we are telling. You mentioned that you can see structures in the monkey brain that predict or that correspond to what you see in the human brain. Obviously, the human brain is doing complex things the monkey brain is not doing. Does that suggest some other more extended, comparatively more virtual overlay, that’s involved in the difference rather than a genes-driven neuro-anatomical organization?

Dr. Terrence Deacon:  The change in the human brain has to be a physical change. That is, the reason that we do what we do and other species don’t with respect to language is clearly something about human brains. In this regard I think there can be no disagreement that there’s something built in to us, something innate that makes us language ready. I think there is no question about that. 

The real question is what kind of thing? What would we have to do, or what did evolution ultimately do to make this brain language ready?  There are all kinds of different ways you could look at that question. 

One is that it built it all in. If I was an engineer I would find all the parts that are necessary to make language and stick it in there, stick in these new parts. The fact that we’ve found no new parts, per se, suggests that that’s probably not the right way to go about the question. But also there’s not a clear sense in which you could look at it as something like a software addition, as if we took the same old computer and put in new software because in fact the computer, so to speak, is different. It’s a really different kind of brain. 

So for me, taking the inside out perspective and looking at brains for clues to language rather than the other way around, I ask the question this way. This is probably the most significant departure from any kind of behavior that we’ve seen in any other species and it’s radically different in many ways from what other species can do. Such a large-scale difference and probably the biggest difference between us and other species ought to be reflected in some of the biggest differences between human brains and non-human brains.   

With that as a kind of guiding hypothesis, not even a hypothesis, a sort of heuristic as to what to look for, I ask the question: So what is different about human brains, if one could categorize in a systematic way, what is really different about human brains? Wouldn’t that tell us something about language? That’s really been the guiding strategy, to some extent, for what I have done over the years. What that amounts to is we, first of all, have to look at the big things, the obvious things.  I say big in a sort of punish sense because what’s really different about human brains is of course they’re bigger. We have always assumed that that’s just some sort of general story about intelligence. The truth is we don’t know much more now about intelligence and what its relationship is to whole brains than we did a century ago. We don’t really know how whole brains work yet. We don’t have a sort of general theory that everybody agrees upon, or even is close to agreeing upon. 

Dr. Terrence Deacon:  On the other hand, this major change, if it’s not just blowing the thing up larger and adding a whole lot more to everything, if it is somehow distributed in an interesting way, that distribution of how the same parts got changed and enlarged with respect to each other might tell us something about what that difference is. In fact, it tells me something very important and that is when you change the size of something you also change the relationships between the parts. We know that a small business, for example, can have one kind of organization for doing things whereas a large business, ultimately just simply because of its size, has to have all kinds of middle managers and different kinds of bureaucracy and people don’t get to talk to everybody. The brain is a different kind of brain because it’s bigger. The connections are going to be different because it’s bigger. That is going to be a clue to it as well. 

I began to look at quantitative issues and with a developmental perspective, how changes in size might change the circuits, that is, how circuits might respond to this. I think for me that has been the biggest source of insights, the biggest source of clues. They’re not answers, they’re clues. That is, I think that the connections are different because the brain is bigger and because not all parts expanded at the same rate. I think that’s the first inside out clue to what is important about this language difference. What was the change in the hardware that supported this new kind of communication and cognition? 

David Boulton:  So, would you say that there was a kind of morphic resonance between the evolution of language and the structures in it and the evolution of the structures in the brain - that there is this kind of resonant co-evolution in the process?

Dr. Terrence Deacon:  I think clearly there was a co-evolutionary process in which language affected brains. The issue is that language changes at a much faster rate than brains. Clearly the language we have today and the kinds of languages that are all over the world were not always the way they are. We undoubtedly passed through not maybe one stage of what you might call a proto language but probably many proto languages, many forms of this linguistic symbolic communication system over the course of our evolution, all of them leaving somewhat of a trace.

David Boulton: In here, but not out there.

Dr. Terrence Deacon:  Yes, inside but not externally. That’s one of the real problems, of course, in studying this. The only trace is in brains that are alive today. We don’t see a trace in the external world. What traces we do see in the archeological record about human evolution are not necessarily useful and directly correspondent maps of what went on the inside of humans. As we know, across the world, people with equal intelligence, equally complex language can be living in radically different cultures with radically different kinds of technologies. Those that can look as the stone age of a million years ago, those that can look as modern as we are today sitting in this studio. The same brains can be producing all of those systems, in part because it is not all inside the head.

Dr. Terrence Deacon:  I want to say one other thing about this correspondence between language and the brain. An engineer might look for something that maps to verbs, maps to nouns, maps to the past tense, all of the various features that linguists tell us that language is broken up into. But language, of course, is broken up according to a logic that has to do with communication, has to do with symbols, has to do with the constraints we have on interacting, perhaps, with speech sounds, perhaps with gesture. The logic of the brain is a very old logic and a very conserved logic. It’s the logic of embryology.  It’s the logic of self organization. In fact, it’s the logic that has been shared with a common ancestor that goes back well before vertebrates.  

We can find hints as to the organization of the genes that develop brains in fly brains. That logic has probably not changed much. That logic is the logic of the organization of brains. There’s unlikely to be a nice, neat direct map between what we see in the external world of language and what we see inside brains. In fact, the map may be very, very confused and very, very different inside the brain, that is, how the brain does what we see externally in language. 

David Boulton: So, the brain is creating out into the world what’s becoming the environment that it is adapting to and language is one major field that it's creating in.

Dr. Terrence Deacon:  Yes. So, in one sense, we should expect the brain to reflect features of language, the features that it’s created. For example, in the metaphor that I used about brains and beaver dams: beaver bodies don’t necessarily reflect beaver dams, they reflect the environment that was created and the demands of that environment. Those demands are not necessarily directly represented in the environment. Beavers are aquatic. Beavers have all kinds of special adaptations for living in water. It’s not easy to predict from what’s produced in the world what’s going to happen inside, so to speak, in the body. I think we can say the same about this troubling and complex dynamic in which language evolution and brain evolution are working in tandem interfering with each other, confusing each other, shaping each other. That dynamic is probably one that is not going to be easy to predict. 

On the other hand, there are a few real general things that we can probably say are consistent. We can say about beavers that whatever their adaptations are going to be, they’re going to be aquatic adaptations. There are some general things about living in the water that you need to know: swimming, breathing, communicating, so on and so forth. One can say that there’s going to be some general things that have to go along with linguistic processing. The symbol processing problem, the automatization, (that is the speeding up of the automatic running of syntax and of analysis), the mnemonic problems, the short term memory problems associated with it  -  these are things that are going to be generally there. And of course, typically the constraints of producing and hearing sound, or producing it visually and manually and interpreting it visually. All of those are things that we could predict so in one sense we can use general characters of language to make predictions. It's probably not going to be very successful if we try to use specific characters of language to make our predictions about brains. 

David Boulton: Can you see the physical trace of cognitive boundaries in the brain?

Dr. Terrence Deacon:  The issue again is that the logic of how brains get built and the logic of how languages get built are different logics.

David Boulton: Right.

Dr. Terrence Deacon:  The logic of brains is this embryology logic that’s very old, very conserved. The logic of language is something that is brand new in the world of evolutionary biology. It happened in one species recently, at least in evolutionary terms.  In that regard, it will be a superficial trace, a tweak, so to speak, on this general pattern. That means that a lot of the details one would expect to find from language are not going to be mapped in any simple, obvious way onto the brain. Therefore, the kind of cognitive distinctions one might expect in language are probably not going to have easy, simple correspondence in functional and structural changes in the brain.

David Boulton: But there is a relationship. I mean, language is stretching our cognitive boundaries.

Dr. Terrence Deacon:  Language clearly forces us to do something that for other species is unnatural and it is that unnaturalness that’s probably the key story. One might want to ask: What is so different about language? What are the aspects of language that are so different from what other species do? To answer the question, what should that imply about how brains have adapted to deal with that? 

David Boulton: So, from a human evolution point of view you would agree with those that basically say that the development of language is the single most distinguishing attribute of human beings today?

Dr. Terrence Deacon:  I do think that the development of language is the single most distinguishing attribute. Now that doesn’t mean speech, necessarily. It means the support system that’s around language - the symbolic system. Of course our communication is much more than linguistic. Some of it is very old also.  But a lot of culture is also linguistic-like in a variety of ways and clearly that has been around a long time. 

The ritual, the mythology…simply ways of doing things that are organized conventionally, symbolically - this is a hallmark of our species. We have, in a sense, transformed and even reinterpreted much of our biology through this system. So much of what we do, whether it’s marriage,  warfare, or whatever, has been transformed by this tool that has, in a sense, taken over and biased all of our interactions with the world. 

David Boulton: I have long wondered what it must have been like to not be verbally self reflexive, to not be aware of myself in this mirror of words, this self talk story that’s going on. And yet it certainly seems that at some point human beings weren’t doing that at the level that we do it now, and, at some other point they were. That is a hugely significant threshold, regardless of where you place it in the evolutionary sequence. 

Dr. Terrence Deacon:  Yes. I think that there are probably many thresholds that we are talking about and early language-like behavior might look very different. I think clearly early language-like behavior had to involve much less vocalization because the brains that preceded us, mammal brains, are not well suited to organizing sound in precise, discrete and rapidly produced learned sequences.

This is something that mammal brains, in effect, are poorly designed to do precisely because the system we use to produce sound is a system that normally should be running on autopilot so that we can breathe appropriately, so that we don’t choke, and so on and so forth.  There’s literally been a change in that circuitry to override those systems in order for language to be possible.

What was language in the past, or what corresponds to language homologically, as they say in biology, the homologues to language might have looked very different. Not a signed language, necessarily, but some very complicated combination of modalities. This makes it very hard to predict what the effects might have been and how those effects were layered upon layer to produce new kinds of languages, new kinds of brains.

Dr. Terrence Deacon:  For me, one of the things I think is really exciting about languages is this aspect of how it reflexively changes the way we think. I think that’s one of the most amazing things about being a human being. 

When people talk about memory they usually talk about two kinds of memory. Episodic memory, remembering a particular thing that happened, a sort of one off event in your past; and then something called procedural memory, the kind of memory that’s involved in skill learning. 

The problem with one-off memory is that there’s so many one-off events, how do you find them again in your memory? The problem with procedural memory is you’ve got to be in the same situation. I know how to ride a bike when you put me on a bike, but if you ask me to tell you exactly which leg I put on first, how do I start out, how do I stay up, I couldn’t tell you because it’s, in a sense, imbedded in its context.

Language is unique in the following sense: that it uses a procedural memory system. Most of what I say is a skill.  Most of my production of the sounds, the processing of the syntax of it, the construction of the sentence, is a skill that I don’t even have to think of. It’s like riding a bicycle. I don’t even have a clue of how I do it.

On the other hand, I can use this procedural memory system because of the symbols that it contains, the meanings and the web of meanings that it has access to, that are also relatively automatic, to access this huge history of my episodes of life so that in one sense it’s using one kind of memory to organize the other kind of memory in a way that other species won’t have access to without this. 

The result is we can construct narratives in which we link together these millions and millions of episodes in our life in which you can ask me what happened last month on a particular day and if I can think through the days of the week and the things I was doing when, I can slowly zero in on exactly what that episodic memory is and maybe even relive it in some sense.

David Boulton: This is a very powerful point. You mentioned before the comparative unnaturalness of this. That at one level we could say that there was, a priori this level of self-reflexive volitional memory recall, a more organismic memory that was less about 'me' remembering and more about re-member-ing me, reassembling me relevantly to the situation that I’m in in nature. So we’re talking about having a verbal, self-reflexive, volitional memory access and control system that little children are picking up when they are two, three and four years old. How well they pick up this complex skill, which is, in the long view of evolution, radically unnatural to their brain, is almost fate determining.

Dr. Terrence Deacon:  Clearly, it changes everything about what being a human being is. Again, I use the phrase, the symbolic species, quite literally, to argue that symbols have literally changed the kind of biological organism we are. Not just in evolution but in day-to-day life.  I think we operate fundamentally different at a cognitive level because of this.

Yet, with just a few tweaks we’re essentially African apes. We’re just a few tweaks away from an African ape. Just enough. Herbert Simon coined this term, satisfycing. It’s not optimizing. It’s just enough to be able to do it. I look at us as an African ape that’s been tweaked just enough to be able to do this radically unnatural kind of activity: language. 

Dr. Terrence Deacon:  Now, it turns out that if satisfycing has been going on for a long time in our evolution then it’s not so unnatural after all, because, of course, brains will have adapted to those demands. This sets up an interesting problem and it speaks to the problem of how old language is. 

If language is new, if language is only a hundred thousand year old, or even less, a fifty or sixty thousand year old kind of process, then we should expect that it has had little effect on human brains - that whatever tweaks were used were, in a sense, clumsy kluges to make the thing work. We shouldn’t expect that it’s easy, that it’s fluid and runs without difficulty. 

On the other hand, if language has been around for a good deal of our evolutionary past, say a few million years, or even a million years, that’s adequate time for it to have structured and reshaped the brain to be better satisficed to the problem of processing and using language in real time. 

Similarly, language will have adapted. We will have adapted this language process to be better fit to our own constraints as we go along. The two will, in a sense, be in tandem, converging towards each other. 

The question one has to ask from the present time looking back is: Are we well adapted to this?  Are we really a symbolic species or is this just a kluge added on top of a primate brain not well designed for this? I think the evidence for the age of this probably can be best picked out by comparing to something quite relevant to what we are discussing, and that is writing and reading.

Dr. Terrence Deacon:  Writing and reading occurred recently. Therefore, whatever we use to do this was a kluge, that is, an engineering patchwork that just sort of barely gets by. We are not well designed to do so and as a result a lot of people have difficulty acquiring reading and writing. There are many kinds of difficulty and many people will never be able to read or write because their brain hasn’t had a chance, so to speak, to keep up with this process.

If language itself were like that we should expect to find those kinds of problems with our ability to acquire language. In fact, I think the surprising feature is that not only is language incredibly complex, it is acquired rapidly in our development, even when children are quite young. Reading, of course, takes quite a while to acquire; you have to wait until your brain has matured a ways. 

But even more interestingly, people with significant brain damage at birth nevertheless do better at language than any other species on the earth, under intense training. That suggests to us that the system has even been over designed a little bit to be prepared with a kind of redundant system in case things go wrong. 

Young children with the whole left hemisphere damaged or removed at a very early age can nevertheless acquire language with half a brain, so to speak. The wrong half, for that matter.  That again suggests the system is somehow over designed. That can only occur if there’s been a long evolutionary history, I think, in which language has played a significant role, suggesting to me that at least, language-like processes are not new, are not recent.

David Boulton: So, you are making a distinction between the comparative unnaturalness of language becoming second nature to us over a vast period of time and the clearly recent invention of writing that we see a few thousand years ago. 

At some point in our language development we evolved speech, which over time folded back on itself to become this self-reflexive awareness system. Now that seems to be the big threshold. When did we begin speaking? Any idea in your own view when that happened? Isn’t that comparatively recent, in the past hundred thousand years spectrum? Don’t our fossil records indicate that the anatomy of our jaws and throat wouldn’t allow for speech until relatively recently?

Dr. Terrence Deacon:  The issue of vocalization, I think, is an important one because, when we look at the brains and the vocal tracts of non-human mammals they are quite different than ours. For me, the vocal tract itself is a secondary feature, though it plays a role. It plays a role in the kinds of sounds that we can produce - the diversity in the range of phonation that we produce as the range of vowels mostly. Even more troublesome is the anatomy of the control of the larynx. 

One of the things that I and a colleague, a graduate student of mine, Alan Sokoloff, pursued over a decade ago was trying to understand the connections between the fore brain and the structures of the larynx and the tongue crucial to language. It turns out that very likely our ancestors, the australopithecines, and of course before them, had, like other mammals, a relatively disconnected control of the larynx and even of the tongue, to some extent. By that I mean that there was probably not much voluntary control over vocalization and certainly not at the level at which you could stop and start it on a dime, so to speak, with very little effort associated with it. 

That changed over the course of evolution and I think we have some clue to that because I think that there’s good reason to suspect that the change in the size of the brain had something to do with the change in control of that system. The secondary signal for that which we actually can see in the fossil record is probably the change in the base of the cranium of the skull and its shape and what it tells us about the position of the larynx. Its role in producing sound, of course, wouldn’t be selectively favored if there wasn’t already a need to produce sound in an articulate way. In other words, the production of vocal speech has to, in a sense, precede and drive and co-evolve with the sound production system externally. 

By the time we begin to see this, and this as we now know precedes human beings, precedes anatomically modern humans going back to the time of homo erectus and the early homo sapiens type, we see some of these changes already occurring. That suggests that already vocalization was being used in a way different probably than other species. 

In this regard, speech, that is the transfer of this communicative task to sound, was probably a slowly evolving, gradually improving feature.  Now why should speech take over from the arms and hands? Well, obviously your arms and hands could be used for other things and it would be nice to free them up. On the other hand, it’s also in some ways easier to mimic the sounds. 

One of the problems in learning language is that we have to learn the sounds of language. To learn a manual display, one has to take in the display that we see and then do a mirror image reversal, because for me to do it I have to take your perspective and do it that way. That’s an extra cognitive step that makes copying true mimicry of behavior a little difficult. However, many species, especially bird species, mimic sound. Because what we hear is not all that different from what we hear when we produce it, we don’t have to go through that extra step. 

It is probably that reason among others that are involved in why speech took over this function more and more over time. I don’t think it’s a case of it suddenly taking over. I think that the evidence we have suggests that it probably took over gradually. As speech becomes more and more an issue there may well be different demands in processing time, in short term memory, and so on and so forth, that go along with it. As we begin to change this system, the whole system has to change around it. Again, all of this makes the study of the evolution of language somewhat more difficult than doing a just so story about when it might have occurred.

David Boulton: The production of speech, the way that we produce speech, the degree of coordination between all these different systems that, as you said before, were at one point running on automatic and became conscripted to the communication system in order to articulate and process communications through sound, didn't this change the shape, time, frequency, packet sizes, whatever you want to call it, of the information exchange that’s going on?

Also, wouldn’t you think that speech had the benefit that you didn’t have to see it?  

Dr. Terrence Deacon:  Yes.

David Boulton: You could be across the tree from each other. You didn’t have to look at each other and be able to see each other’s gestures to be able to communicate so you could coordinate at a greater distance. But relative to where our story goes ultimately, one of the things that we’re talking about, of course, is that reading, at least initially, when children are developing the skill, has to overlay speech.  So, it has to work inside the constraints of the existing language processing infrastructure. It has to take this code and simulate the assembly of the speech processes that generate virtually heard or actually spoken word sounds. The timing of how this construction has to work has to fit inside of the timing constraints and structural constraints we evolved to process speech. What have you discovered in the past decade, when you were doing this kind of research, or subsequently, that casts any light on the timing coordination of the different component parts involved in this dance called speech?

Dr. Terrence Deacon:  The timing is not something that I have done direct work on. However, something that's relevant to that is that I think we can learn quite a bit about the neurological problem by looking at how writing systems themselves have evolved. In a social sense it’s evolving in response to changes that stuck or didn’t stick in these various systems. The few times that language has turned into writing, become externalized in the world, almost all began with a kind of pictorial mode. The problem with pictures is that, of course, they’re not like sound, not like language. The advantage of pictures is that they’re much closer to what they represent, in some sense. We can even look at some of these ancient writing systems and make some educated guesses and it turns out usually they’re wrong for interesting reasons. One of those reasons is that almost as soon as picture-like writing came about people began to use the pictures to also represent sounds, the name of things, a rebus, like you find in a coke bottle cap, in which you’re trying to figure out the meaning of something by using a picture to represent a sound also. 

Most of the pictorial writing systems very quickly took on sound iconism, that is sound likeness as well. The word for that thing has a sound and I can use that sound element to put together with other sound elements. What happened was that kind of system got co-opted very quickly. Now in one sense you can say, well this is a disadvantage because the interpretation of the meaning might be easier if you could see the picture, if you got something about the picture of it right away, because vision is one of the ways we remember objects and relationship. On the other hand, it’s broken up into bits and pieces, it’s separated. And of course it’s quite distant from speech. Speech has recoded this in a whole different way. What seems to have happened in most of the world’s written forms, not all of them, but even those that still have a bit of pictorial nature to them, even have acquired this feature, and that is, that they have become representations of the speech stream itself, and only secondarily of something in the world.

David Boulton:  In your book you make an interesting correlate to this point and that is that the evolution of language is more reflective of the child’s ability to learn it rather than the adult’s ability to use it. This is something that creates quite a contrast because I think that’s not the case with writing systems. Writing systems are an invention of adults for adults. There hasn’t been the same degree of evolutionary loop concerning itself with how well it fits the child.

Dr. Terrence Deacon:  Yes. I think one of the really interesting things about writing is how long it takes before we’re mature enough, before our brain is ready to acquire it and to do it easily because the learning process there is clumsy. With respect to speech or even sign languages, the learning process is already set up. From a very early age, in fact, we’re able to do things that, if one was just to look at the complexity of the task, would seem infinitely more complex than interpreting these letters and figuring out how letters map to sounds. I think that that’s a real paradox that makes the reading and writing problem stand out.  

There's another feature to this in which writing has adapted to some of the constraints of adults using it, of course, whereas speech and signing have probably adapted more to children acquiring it. The reason I say that is that the only languages that can be passed on down effectively and efficiently are those that can be picked up quickly and easily at the youngest possible age.

Why at the youngest possible age? Because if you have to use this for everything you do, to some extent you want to acquire it in a way that’s most suited to your brain, in which most of your resources have been organized with respect to it. Early on brains are quite plastic, quite flexible. The result is the more experience with language we have very early, the better we are at it as adults. Those who have been deprived in one way or another of that experience are quite poor in their linguistic abilities as adults, some never acquiring some of the features of language.

So, to some extent, the very specialization that we have for acquiring language and acquiring it at an early age amplifies this difference in human brains. That brains come in to the world, so to speak, expecting to be bombarded with language at an early age as part of its organizing principle, and that human brains that don’t get that experience, in effect, are not getting the normal nutritive experience of their expected evolutionary anticipation of this kind of environment that they’re about to fall into.

David Boulton:  Back to our story and another place that we can plug in here. Building on a point from a moment ago, we talked about language adapting itself according to how learnable it is to young children because that’s what’s selecting it, and so they’ve grown together - that’s where the co-evolutionary linkage is the most powerful between humans and language.

Dr. Terrence Deacon:  Right.

David Boulton: But writing systems are adult inventions that are on the other side of this language learning barrier, on the other side of this abstract self-reflexiveness, and it requires different kinds of processing than is natural to the child or to spoken language acquisition. 

One of the things that’s mo