Symbolic Species: The Co-Evolution of Language and the Brainby Terrence W. Deacon
"A work of enormous breadth, likely to pleasantly surprise both general readers and experts."—New York Times Book Review
This revolutionary book provides fresh answers to long-standing questions of human origins and consciousness. Drawing on his breakthrough research in comparative neuroscience, Terrence Deacon offers a wealth of insights into the
"A work of enormous breadth, likely to pleasantly surprise both general readers and experts."—New York Times Book Review
This revolutionary book provides fresh answers to long-standing questions of human origins and consciousness. Drawing on his breakthrough research in comparative neuroscience, Terrence Deacon offers a wealth of insights into the significance of symbolic thinking: from the co-evolutionary exchange between language and brains over two million years of hominid evolution to the ethical repercussions that followed man's newfound access to other people's thoughts and emotions.
Informing these insights is a new understanding of how Darwinian processes underlie the brain's development and function as well as its evolution. In contrast to much contemporary neuroscience that treats the brain as no more or less than a computer, Deacon provides a new clarity of vision into the mechanism of mind. It injects a renewed sense of adventure into the experience of being human.
To those outside the immediate family, it's sometimes difficult to see the charm of the newborn child. Babies have no useful skills. They can't perform any tricks. All they seem able to do is to produce enormous amounts of noise and excrement. An observer might be forgiven for dismissing them, at this stage, as little more than exceptionally maladroit, hairless pets. But at a certain point -- unlike, say, kittens -- babies begin to speak. And then even the most cynical child-hater has to give way, for a moment at least, to a sort of wonder.
Linguists have been as puzzled by this accomplishment as the rest of us: How is it that small children, who seem so perplexed by the simple task of keeping food on a tray, can so easily pick up something as complicated as language? Many linguists, following the lead of Noam Chomsky, have argued that language is, in effect, hardwired into the brain. To Terrence Deacon, a brain researcher at Boston University and Harvard Medical School, this explanation begs a larger question. It's a bit like saying (as a character in Molière's "Imaginary Invalid" famously did) that opium induces sleep because it contains a "soporific factor." The real question is: How did we get language embedded in our heads in the first place?
In The Symbolic Species, Deacon offers a marvelously seductive, if speculative, answer. Abandoning the "chicken or the egg" debate about what came first, he suggests that language and the human brain evolved together. "From this perspective language must be viewed as its own prime mover," Deacon writes. "Modern languages, with their complex grammar and syntax, their massive vocabularies ... evolved incrementally from smaller beginnings ... and the brains that originally struggled to support simple languages were replaced by brains better suited to this awkward adaptation." Once our ancestors stumbled onto the awesome power of language, "it sent our lineage of apes down a novel evolutionary path -- a path that has continued to diverge from all other species ever since." And while our brains have adapted to language, language has itself adapted to our brains. One of the main reasons small children "appear preadapted to guess the rules of syntax correctly," Deacon suggests, is that syntax itself has adapted itself to the patterns most regularly guessed by generation after generation of children.
Although Deacon's central insight is simple and powerful, The Symbolic Species is not always clear or convincing in its details. Deacon draws on research in diverse fields, ranging from linguistics to medicine, and delves deeply into the biology of human and animal brains. Much of the book, however, is frankly conjectural, and many of Deacon's more imaginative scenarios (whether they have to do with the sex lives of Homo erectus or the possibility of man-made thinking machines) are clearly less than fully proven. And for all his understanding of language in the abstract, Deacon has some trouble making himself understood -- hiding some of his most radical conclusions in the midst of long and convoluted arguments and (like a researcher teaching signs to a recalcitrant chimp) repeating himself endlessly to little effect. Nevertheless, The Symbolic Species offers a serious challenge to scientists in a variety of fields -- and to anyone with the fortitude to plow through its 500 pages. -- Salon
- Norton, W. W. & Company, Inc.
- Publication date:
- Sales rank:
- Product dimensions:
- 6.00(w) x 8.90(h) x 1.20(d)
Read an Excerpt
The Human Paradox
... the paradox is the source of the thinker's passion, and the thinker without a paradox is like a lover without feeling: a paltry mediocrity.
An Evolutionary Anomaly
As our species designation--sapiens--suggests, the defining attribute of human beings is an unparalleled cognitive ability. We think differently from all other creatures on earth, and we can share those thoughts with one another in ways that no other species even approaches. In comparison, the rest of our biology is almost incidental. Hundreds of millions of years of evolution have produced hundreds of thousands of species with brains, and tens of thousands with complex behavioral, perceptual, and learning abilities. Only one of these has ever wondered about its place in the world, because only one evolved the ability to do so.
Though we share the same earth with millions of kinds of living creatures, we also live in a world that no other species has access to. We inhabit a world full of abstractions, impossibilities, and paradoxes. We alone brood about what didn't happen, and spend a large part of each day musing about the way things could have been if events had transpired differently. And we alone ponder what it will be like not to be. In what other species could individuals ever be troubled by the fact that they do not recall the way things were before they were born and will not know what will occur after they die? We tell stories about our real experiences and invent stories about imagined ones, and we even make use of these stories to organize our lives. In a real sense, we live our lives in this shared virtual world. And slowly, over the millennia, we have come to realize that no other species on earth seems able to follow us into this miraculous place.
We are all familiar with this facet of our lives, but how, you might ask, could I feel so confident that it is not part of the mental experience of other species--so sure that they do not share these kinds of thoughts and concerns--when they cannot be queried about them? That's just it! My answer which will be argued in detail in the following chapters, has everything to do with language and the absence of it in other species. The doorway into this virtual world was opened to us alone by the evolution of language, because language is not merely a mode of communication, it is also the outward expression of an unusual mode of thought--symbolic representation. Without symbolization the entire virtual world that I have described is out of reach: inconceivable. My extravagant claim to know what other species cannot know rests on evidence that symbolic thought does not come innately built in, but develops by internalizing the symbolic process that underlies language. So species that have not acquired the ability to communicate symbolically cannot have acquired the ability to think this way either.
The way that language represents objects, events, and relationships provides a uniquely powerful economy of reference. It offers a means for generating an essentially infinite variety of novel representations, and an unprecedented inferential engine for predicting events, organizing memories, and planning behaviors. It entirely shapes our thinking and the ways we know the physical world. It is so pervasive and inseparable from human intelligence in general that it is difficult to distinguish what aspects of the human intellect have not been molded and streamlined by it. To explain this difference and describe the evolutionary circumstances that brought it about are the ultimate challenges in the study of human origins.
The question that ultimately motivates a perennial fascination with human origins is not who were our ancestors, or how they came to walk upright, or even how they discovered the use of stone tools. It is not really a question that has a paleontological answer. It is a question that might otherwise be asked of psychologists or neurologists or even philosophers. Where do human minds come from? The missing link that we hope to fill in by investigating human origins is not so much a gap in our family tree, but a gap that separates us from other species in general. Knowing how something originated often is the best clue to how it works. And we know that human consciousness had a beginning. Those features of our mental abilities that distinguish us from all other species arose within the handful of million years since we shared a common ancestor with the remaining African apes, and probably can mostly be traced to events that took place only within the last 2 million. It was a Rubicon that was crossed at a definite time and in a specific evolutionary context. If we could identify what was different on either side of this divide--differences in ecology, behavior, anatomy, especially neuroanatomy--perhaps we would find the critical change that catapulted us into this unprecedented world full of abstractions, stories, and impossibilities, that we call human.
It is not just the origins of our biological species that we seek to explain, but the origin of our novel form of mind. Biologically, we are just another ape. Mentally, we are a new phylum of organisms. In these two seemingly incommensurate facts lies a conundrum that must be resolved before we have an adequate explanation of what it means to be human.
Advances in the study of human evolution, the brain, and language processes have led many scientists confidently to claim to be closing in on the final clues to this mystery. How close are we? Many lines of evidence seem to be converging on an answer. With respect to our ancestry, the remaining gaps in the fossil evidence of our prehistory are being rapidly filled in. Within the last few decades a remarkably rich picture of the sizes and shapes of fossil hominid bodies and brains has emerged. It is probably fair to say that at least with respect to the critical changes that distinguish us in this way from other apes, there are few missing links yet to be found, just particulars to be filled in. That crucial phase in hominid evolution when our ancestors' brains began to diverge in relative size from other apes' brains is well bracketed by fossils that span the range. As for the inside story, the neurosciences are providing powerful new tools with which it has become possible to obtain detailed images from working human brains performing language tasks, or to investigate the processes that build our brains during development and distinguish the brains of different species, or even to model neural processes outside of brains. Finally, linguists' analyses of the logical structure of languages, their diversity and recent ancestry, and the patterns that characterize their development in children have provided a wealth of information about just what needs to be explained, and comparative studies of animals' communications in the wild and their languagelike capacities in the laboratory have helped to frame these questions with explicit examples.
Despite all these advances, some critical pieces of the puzzle still elude us. Even though neural science has pried ever deeper into the mysteries of brain function, we still lack a theory of global brain functions. We understand many of the cellular and molecular details, we have mapped a number of cognitive tasks to associated brain regions, and we even have constructed computer simulations of networks that operate in ways that are vaguely like parts of brains; but we still lack insight into the general logic that ties such details together. On the whole, most neuroscientists take the prudent perspective that only by continuing to unmask the details of simple neural processes in simple brains, and slowly, incrementally, putting these pieces together, will we ever be able to address such global theoretical questions as the neural basis for language. We must add to this many new problems arising out of the comparisons of animal communication to language. If anything, these problems have become more complex and more confusing the more we have learned about the sophistication of other species' abilities and the paradoxes implicit in our own abilities. But the most critical missing piece of the puzzle is access to the brains in question: ancestral hominid brains. Though we have considerable information about brain sizes in fossil species, and a little information about brain shapes, the relevant anatomical information, the internal microarchitecture of these brains, has left no fossil trail. With respect to fossil brains, we will never find the "smoking gun"--the first brain capable of language. We will only have access to circumstantial information.
So, what business do we have speculating about the beginnings of language? Given the complexity of the human brain, our current ignorance of many of its crucial operating principles, and the fact that neither languages nor the brains that produce them fossilize, there would appear to be many more immediate questions to be answered before even considering this one. There seem to be too many loose ends and gaps in the supportive evidence to provide solid leads in the search for clues to the nature of the human mind in the origins of language.
But this ignores the significance of the fact that language is a one-of-a-kind anomaly. Often the most salient and useful hints about the underlying logic of nature's designs are provided when unique or extreme features in two different domains are found to be correlated. Some notable examples include the correlation between superconductivity and extreme cold; between greater cosmic distances and the increasing redness of starlight; between the massive extinctions of fossil species and evidence of extraterrestrial impacts; between the peculiarity of haplo-diploid genetics and war, suicidal defense, and infertile castes in social insects; and so on. Each of these correlations cried out for an explanation and in so doing offered a critical clue to a more general principle. The more two related features diverge from what is typical in their respective domains, the more penetrating the insight that can be gleaned from their underlying relationship.
In this context, then, consider the case of human language. It is one of the most distinctive behavioral adaptations on the planet, Languages evolved in only one species, in only one way, without precedent, except in the most general sense. And the differences between languages and all other natural modes of communicating are vast. Such a major shift in behavioral adaptation could hardly fail to have left its impression on human anatomy. Even superficial appearances bear this out. We humans have an anomalously large brain and a uniquely modified vocal tract. Though these clues offer no more than a starting point, they suggest that the structural and functional relationships underlying these superficial correlations are likely to be robust and idiosyncratic to us.
Ironically, then, the problem of language origins may actually offer one of the most promising entry points in the search for the logic linking cognitive functions to brain organization. To the extent that the unique mental demands of language are reflected in unique neuroanatomical differences, we may find an unequivocal example of how nature maps cognitive differences to brain structure differences. Though the details of this mystery are challenging, no critical pieces of this puzzle lie buried in the deep evolutionary past or inaccessible to current technology. They are observable in the differences in cognitive abilities and brain structures to be found in living species.
I think that the difficulty of the language origins question is not to be blamed on what we don't know, but rather on what we think we already know. We think we know that what keeps language from being a widespread phenomenon is its byzantine complexity and the incredible demands it places on learning and memory. We think we know that language became possible for our ancestors when these impediments to language learning were overcome by some prior change in the brain. Depending on which aspects of language are deemed to be most complex, different prior adaptations are invoked to explain how language became possible. Perhaps it required an increase in intelligence, a streamlining of oral and auditory abilities, a separation of functions to the two sides of the brain, or the evolution of a sort of built-in grammar. I think we can be sure of none of these things. In fact, I think that the problem is more basic and far more counterintuitive than is assumed by any of these accounts.
There are a few common assumptions shared by all of these explanations that I think are the root of a deeper problem. In general, these arguments parallel many others that continually resurface along that age old divide between nature and nurture. Is language imposed from the outside or does it reflect what is already inside? For decades, the superficiality of this stale dichotomy has been evident, exposed by research in the psychological and biological sciences that demonstrates how truly complex and interdependent the biological and environmental contributions to development can be; but we still find it difficult to conceive of these phenomena in other terms. We have reinvented the same old answers in new guises in each generation, stubbornly insisting that the answer to the question of language knowledge must be found in one of just a few major alternative paradigms (depicted in cartoon fashion in Figure 1.1).
At one end of this spectrum is the assumption that the architecture of language originates entirely outside (simple associationism); at the other end is the assumption that it originates entirely inside (mentalese). What other alternatives could there be, that are not captured between these extremes? And if there are no other alternatives, then shouldn't answering this question also point to the solution to the language origins question? Discovering which aspects of language knowledge are contributed by nature and which by nurture ought to tell us what difference in us was necessary to bridge the original language acquisition gap. If the answer lies more toward the associationist end of the spectrum, then evolution must have given us language by endowing us with exceptionally powerful learning and memory. If the answer lies more toward the mentalese end, then evolution must have endowed us with remarkably sophisticated instinctual knowledge of language that made learning completely unnecessary.
In light of these intuitively compelling alternatives, the approach I am about to take may seem misguided. Not only do I think that these alternatives confuse the nature/nurture problem more than they illuminate it, I think that the whole question of where language knowledge originates during development is secondary. Though a young child's almost miraculous development of language abilities is indeed a remarkable mystery--one that will be considered in some detail later (in Chapters 4 and 11)--I think that the cause of language origins must be sought elsewhere, and by pursuing some very different kinds of research questions. While we have been worrying about where knowledge of language comes from, we have been avoiding a more basic question: What sort of thing is knowledge of language anyway? Before turning to this question, however, it is worth while reflecting on some of the equally misleading evolutionary assumptions that reinforce the traditional theoretical alternatives.
Technical Difficulties and Hopeful Monsters
One of the most common views about language evolution is that it is the inevitable outcome of evolution. Evolution was headed this way, our way As the only species capable of conceiving of our place among all others, we see what looks like a continuous series of stages leading up to one species capable of such reflections. It goes without saying that a more articulate, more precise, more flexible means of communicating should always be an advantage, all other things being equal. In terms of cooperative behaviors, a better ability to pass on information about distant or hidden food resources, or to organize labor for a hunt, or to warn of impending danger, would be advantageous for kin and the social group as a whole. Better communication skills might also contribute to more successful social manipulation and deception. The ability to convince and mislead one's competitors or cooperate and connive with one's social and sexual partners could also have provided significant reproductive advantages, particularly in social systems where competition determines access to defendable resources or multiple mates. In fact, it's difficult to imagine any human endeavor that would not benefit from better communication. Looked at this way, it appears that humans have just developed further than other species along an inevitable progressive trend toward better thinking and better communicating.
Surely we must be part of a trend of better communication in some form? It seems to be an unstated assumption that if biological evolution continues long enough, some form of language will eventually evolve in many other species. Are chimpanzees the runners-up, lagging only a little behind on the road to language? As in Planet of the Apes, a science fiction movie in which our more hairy cousins catch up to a human level of mental and liguistic abilities, we imagine that if given sufficient time, something like language is prefigured in evolution. We even imagine that if there is life on other planets, and if it has been evolving as long as life on earth, or longer, there will be "intelligent" species with whom we may someday converse. The Renaissance notion of a "Great Chain of Being" gave rise to nineteenth-century theories of phylogeny that ranked species from lower to higher, from mechanism to godly, with humans just below angels. Though later nineteenth- and twentieth-century evolutionists rejected the static ranking of phylogeny and replaced it with the theory of evolutionary descent, the anthropocentric perspective was simply rephrased in evolutionary terms. Humans were presumably the most "advanced" species. Carrying this notion to its extreme, some people now suspect that there may be spaceships visiting earth, carrying beings that are "more highly evolved" than we are.
On the surface, progress seems to be implicit in natural selection. Gradual improvement of adaptations seems to imply that the longer evolution continues the better the design will become. Indeed, many scientists talk as though a special kind of retrograde selection would be necessary to halt the progress of inevitably increasing intelligence. Small-brained species are often considered primitive or throwbacks to earlier forms, left out of the main trend. From an anthropocentric perspective, it seems unquestionable that more intelligent species will outcompete less intelligent ones. Intelligence is always an advantage, right? Brain over brawn. We rank genius and mental retardation on a single scale, and presumably rank chimpanzees, dogs, and rats on the low end of the same scale. Human evolution is often termed an "ascent" to imply a climb from lower to higher intelligence. And from this it seems to follow that humans are just the pinnacle example of an inevitable trend. The winner in a war of neurons.
The apparent reasonableness of this view reflects our familiarity with technological progress in Western societies. The interchangeability of terms like consciousness expansion, social progress, and evolution is now almost commonplace in the popular press, and these ideas are seldom entirely disentangled even in the most sophisticated accounts of human evolution. But the idea of progress in evolution is an unnoticed habit left over from a misinformed common sense, from seeing the world in terms of design. The problem is that our intuitive model for evolution is borrowed from the history of technological change, which has been a cumulative process, adding more and more habits of know-how to the growing mass of devices, practices, and records each day. In contrast, biological evolution is not additive, except in some very limited ways. The human repertoire of expressed genes is about the same as that in a mouse or frog, and the body plans of all vertebrates seem to be mostly modifications of the same shared plan--even for the brain. Though we are on the large end of the range of body and brain sizes, this is not the result of adding new organs but merely enlarging existing ones with slight modifications.
Evolution is an irreversible process, a process of increasing diversification and distribution. Only in this sense does evolution exhibit a consistent direction. Like entropy, it is a process of spreading out to whatever possibilities are unfilled and within reach of a little more variation. Evolution does not continue to churn out ever better mousetraps, even if it has produced some remarkable examples along the way. But this pattern of spreading into unfilled niches does place us in one of the more extreme niches.
Evolution is diversification in all directions, but there are more options available in some directions than others. Organisms started out small and short-lived and couldn't get much smaller, but they could always get larger and more long-lived. For the smallest organisms, the resources that can be devoted to internal representations of the world are limited, though even bacteria appear able to use their one information-storage system, their genes, to take in information from around them and modify their behaviors appropriately. But the upper end of the range of information-handling abilities was not similarly bounded, and so the difference between the low end and the upper end of this range has increased over the hundreds of million years of animal evolution as part of this diversification. Nevertheless the number of small-brained creatures has not diminished because of competition with those with big brains, and the no-brainers--all the plants and single-celled organisms--vastly outnumber the rest of us. It just happens that one very, very minor evolutionary direction is toward niches where doing a lot of information processing during one's life is a good way to pass on genes. Inevitable? Well, it's about as inevitable a direction in evolution as the development of arctic fish with antifreeze in their blood or electric eels who use electricity to sense their way through muddy Amazonian waters. The niche was just there, and was eventually filled Still, in some measure, we are near the extreme of this distribution.
The question, then, is whether the evolution of language was somehow prefigured in this trend. Is there a general trend toward better communication? It's easy in hindsight to arrange the history of long-distance communication from telegraphs to telephones to cellular phones to Star Trek communicators. It is not so easy to determine if animal communication has been steadily getting better and if human language is a part of such a trend. Certainly, there were advances in distance and signal clarity in evolution, but even if we narrow our comparison to vocal communication, there is no evidence in living species that some inevitable progressive trend leads to us. Apparently simple species can use highly complex methods of sound communication, and some highly complex species can be oblivious to their advantages. There are also many great sound tricks, such as echolocation that are completely beyond human ability. Among our closest relatives, the great apes, there are both highly vocal (chimp) and nearly silent (orangutan) species. In fact, most birds easily outshine any mammal in vocal skills, and though dogs, cats, horses, and monkeys are remarkably capable learners in many domains, vocalization is not one of them. Our remarkable vocal abilities are not part of a trend, but an exception.
We also tend to underestimate the complexity and subtlety of much nonhuman social communication. In recent decades, field studies of social communication in nonhuman species have demonstrated that many birds, primates, and social carnivores use extensive vocal and gestural repertoires to structure their large social groups. These provide a medium for organizing foraging and group movement, for identifying individuals, for maintaining and restructuring multidimensional social hierarchies, for mediating aggressive encounters, for soliciting aid, and for warning of dangers. Indeed, even in our own species, a rich and complex language is still no substitute for a shocked expression, a muffled laugh, or a flood of silent tears, when it comes to communicating some of the more important messages of human social relationships.
However, although they are complex, these elaborate repertoires of calls, displays, and gestures do not seem to map onto any of the elements that compose languages. Although various researchers have suggested that parallels to certain facets of language are to be found in the learned dialects of birdsong, the external reference evident in vervet monkey alarm calls or honeybee dances, and the socially transmitted sequences of sounds that make up humpback whale songs (each of which will be considered in some detail in Chapter 2), these and many other examples like them only exhibit a superficial resemblance to language learning, word reference, or syntax, respectively. Even if we were to grant these parallels, no nonhuman species appears to put these facets of language together into a coordinated, rule-governed system.
Could we have missed recognizing nonhuman languages because they are as alien to us as our speech is to them? People have long entertained this possibility at least in mythology and children's stories. They offer the fantasy that we might someday overcome the communication boundaries that separate humans and other animals and share memories, beliefs, hopes, and fears with them. In the popular children's book made into a movie, Dr. Doolittle enlists the aid of a "multilingual" parrot to translate between animal and human speech. But is even a very superficial "translation" possible? What do you tell a child who asks, "What is the kitty saying?" Do animals' vocalizations and gestures explain, describe, ask, or command? Do they argue, disagree, bargain, gossip, persuade, or entertain one another with their thoughts? Are there any corresponding elements in animal communication that map onto the elements of human language? Unfortunately, animal calls and displays have nothing that corresponds to noun parts or verb parts of sentences, no grammatical versus ungrammatical strings, no marking of singular or plural, no indications of tense, and not even any elements that easily map onto words, except in the most basic sense of the beginning and ending of a sound.
One quite reasonable caution against making strong claims about the absence of nonhuman languages is that our study of other species' communication systems is still in its infancy. Isn't it more prudent to remain agnostic until we have learned a great deal more about other species communications? It is always wise not to prejudge the evidence, especially with respect to a subject about which we have undeniable prejudices. And there are far more species about whose communicative behavior we know next to nothing than there are whose communication has been studied. Nevertheless I think that we have sufficient information to make a reasonably confident claim even about species whose communicative behaviors have been only superficially studied. What makes this a fairly safe guess is not the sophistication of our behavioral analyses, but rather the striking characteristics that would be evident in a nonhuman language. Where the differences should be glaring, the sensitivity and sophistication of observations and tests can be minimal.
What would be the characteristics of a nonhuman language that would allow us instantly to recognize it as a languagelike form of communication even if it were quite alien with respect to all human languages? This is the sort of question that scientists scanning the heavens with radio telescopes listening for signals from unearthly species must ask themselves, or that might be asked by those engaged in electronic surveillance interested in distinguishing the transmission of coded or encrypted signals from random noise. Interestingly, many of these characteristics are exhibited in the surface structure of the signals, and require no special insight into meaning or referential function, and no obvious correspondence with natural language grammars, to discern. Here are a few general features that ought to stand out. A languagelike signal would exhibit a combinatorial form in which distinguishable elements are able to recur in different combinations. It would exhibit a creative productivity of diverse outputs and a rather limited amount of large-scale redundancy. And although there would be a high degree of variety in the possible combinations of elements, the majority of combinatorial possibilities would be systematically excluded. In terrestrial examples, where it would be possible to observe the correlations between signals and contextual events, there should be another rather striking and counterintuitive feature. The correlations between individual signals and the objects and events that form the context of their production should not exhibit a simple one-to-one mapping. The correlations between sign elements and their pragmatic context should differ radically yet systematically from occasion to occasion, depending on how the signals are arranged in combination with respect to one another. These, of course, are all general features associated with syntax, though not just language syntax. Human games, mathematics, and even cultural customs exhibit these features.
If a radio-telescope observer identified a signal emanating from distant space with these characteristics it would make world headlines, despite the fact that the meaning of the signal would remain completely undecodable. With far more to go on than this, in even superficially studied animal communications, we can be reasonably sure that for the vast majority of likely candidate species such a signal has not yet been observed. Instead, though highly complex and sophisticated, the communicative behaviors in other species tend to occur as isolated signals, in fixed sequences, or in relatively unorganized combinations better described by summation than by formal rules. And their correspondences with events and behavioral outcomes, in the cases where this can be investigated, inevitably turn out to be of a one-to-one correlational nature. Though an as yet undescribed example of an animal communication system that satisfies these criteria cannot be ruled out, it seems reasonable to conclude that the chances are poor that it would have gone unobserved in common animal species, any more than we would miss it in a cosmic radio signal.
and post it to your social network
Most Helpful Customer Reviews
See all customer reviews >