Origin of speech
The origin of speech refers to the more general problem of the origin of language in the context of the physiological development of the human speech organs such as the tongue, lips and vocal organs used to produce phonological units in all human languages.
Although related to the more general problem of the origin of language, the evolution of distinctively human speech capacities has become a distinct and in many ways separate area of scientific research. The topic is a separate one because language is not necessarily spoken: it can equally be written or signed. Speech is in this sense optional, although it is the default modality for language.
Uncontroversially, monkeys, apes and humans, like many other animals, have evolved specialised mechanisms for producing sound for purposes of social communication. On the other hand, no monkey or ape uses its tongue for such purposes. Our species' unprecedented use of the tongue, lips and other moveable parts seems to place speech in a quite separate category, making its evolutionary emergence an intriguing theoretical challenge in the eyes of many scholars.
The term modality means the chosen representational format for encoding and transmitting information. A striking feature of language is that it is modality-independent. Should an impaired child be prevented from hearing or producing sound, its innate capacity to master a language may equally find expression in signing. Sign languages of the deaf are independently invented and have all the major properties of spoken language except for the modality of transmission. From this it appears that the language centres of the human brain must have evolved to function optimally irrespective of the selected modality.
"The detachment from modality-specific inputs may represent a substantial change in neural organization, one that affects not only imitation but also communication; only humans can lose one modality (e.g. hearing) and make up for this deficit by communicating with complete competence in a different modality (i.e. signing)."— Marc Hauser, Noam Chomsky and W. Tecumseh Fitch, 2002. The Faculty of Language: What Is It, Who Has It, and How Did It Evolve?
This feature is extraordinary. Animal communication systems routinely combine visible with audible properties and effects, but not one is modality-independent. No vocally impaired whale, dolphin or songbird, for example, could express its song repertoire equally in visual display. Indeed, in the case of animal communication, message and modality are not capable of being disentangled. Whatever message is being conveyed stems from intrinsic properties of the signal.
Modality independence should not be confused with the ordinary phenomenon of multimodality. Monkeys and apes rely on a repertoire of species-specific "gesture-calls" — emotionally expressive vocalisations inseparable from the visual displays which accompany them. Humans also have species-specific gesture-calls — laughs, cries, sobs and so forth — together with involuntary gestures accompanying speech. Many animal displays are polymodal in that each appears designed to exploit multiple channels simultaneously.
The human linguistic property of "modality independence" is conceptually distinct from this. It allows the speaker to encode the informational content of a message in a single channel, while switching between channels as necessary. Modern city-dwellers switch effortlessly between the spoken word and writing in its various forms — handwriting, typing, e-mail and so forth. Whichever modality is chosen, it can reliably transmit the full message content without external assistance of any kind. When talking on the telephone, for example, any accompanying facial or manual gestures, however natural to the speaker, are not strictly necessary. When typing or manually signing, conversely, there's no need to add sounds. In many Australian Aboriginal cultures, a section of the population — perhaps women observing a ritual taboo — traditionally restrict themselves for extended periods to a silent (manually signed) version of their language. Then, when released from the taboo, these same individuals resume narrating stories by the fireside or in the dark, switching to pure sound without sacrifice of informational content.
Evolution of the speech organsEdit
Speaking is the default modality for language in all cultures. Humans' first recourse is to encode our thoughts in sound — a method which depends on sophisticated capacities for controlling the lips, tongue and other components of the vocal apparatus.
The speech organs, everyone agrees, evolved in the first instance not for speech but for more basic bodily functions such as feeding and breathing. Nonhuman primates have broadly similar organs, but with different neural controls. Apes use their highly flexible, maneuverable tongues for eating but not for vocalizing. When an ape is not eating, fine motor control over its tongue is deactivated. Either it is performing gymnastics with its tongue or it is vocalising; it cannot perform both activities simultaneously. Since this applies to mammals in general, Homo sapiens is exceptional in harnessing mechanisms designed for respiration and ingestion to the radically different requirements of articulate speech.
The word "language" derives from the Latin lingua, "tongue". Phoneticians agree that the tongue is the most important speech articulator, followed by the lips. A natural language can be viewed as a particular way of using the tongue to express thought.
The human tongue has an unusual shape. In most mammals, it's a long, flat structure contained largely within the mouth. It is attached at the rear to the hyoid bone, situated below oral level in the pharynx. In humans, the tongue has an almost circular sagittal (midline) contour, much of it lying vertically down an extended pharynx, where it is attached to a hyoid bone in a lowered position. Partly as a result of this, the horizontal (inside-the-mouth) and vertical (down-the-throat) tubes forming the supralaryngeal vocal tract (SVT) are almost equal in length (whereas in other species, the vertical section is shorter). As we move our jaws up and down, the tongue can vary the cross-sectional area of each tube independently by about 10:1, altering formant frequencies accordingly. That the tubes are joined at a right angle permits pronunciation of the vowels [i], [u] and [a], which nonhuman primates cannot do. Even when not performed particularly accurately, in humans the articulatory gymnastics needed to distinguish these vowels yield consistent, distinctive acoustic results, illustrating the quantal nature of human speech sounds. It may not be coincidental that [i], [u] and [a] are the most common vowels in the world's languages.
In humans, the lips are important for the production of stops and fricatives, in addition to vowels. Nothing, however, suggests that the lips evolved for those reasons. During primate evolution, a shift from nocturnal to diurnal activity in tarsiers, monkeys and apes (the haplorhines) brought with it an increased reliance on vision at the expense of olfaction. As a result, the snout became reduced and the rhinarium or "wet nose" was lost. The muscles of the face and lips consequently became less constrained, enabling their co-option to serve purposes of facial expression. The lips also became thicker. "Hence", according to one major authority, "the evolution of mobile, muscular lips, so important to human speech, was the exaptive result of the evolution of diurnality and visual communication in the common ancestor of haplorhines". It is unclear whether our lips have undergone more recent adaptation to the specific requirements of speech.
Compared with nonhuman primates, humans have significantly enhanced control of breathing, enabling exhalations to be extended and inhalations shortened as we speak. While we are speaking, intercostal and interior abdominal muscles are recruited to expand the thorax and draw air into the lungs, and subsequently to control the release of air as the lungs deflate. The muscles concerned are markedly more innervated in humans than in nonhuman primates. Evidence from fossil hominins suggests that the necessary enlargement of the verterbral canal, and therefore spinal cord dimensions, may not have occurred in Australopithecus or Homo erectus but was present in the Neanderthals and early modern humans.
The larynx or voice box is an organ in the neck housing the vocal folds, which are responsible for phonation. In humans, the larynx is descended. Our species is not unique in this respect: goats, dogs, pigs and tamarins lower the larynx temporarily, to emit loud calls. Several deer species have a permanently lowered larynx, which may be lowered still further by males during their roaring displays. Lions, jaguars, cheetahs and domestic cats also do this. However, laryngeal descent in nonhumans (according to Philip Lieberman) is not accompanied by descent of the hyoid; hence the tongue remains horizontal in the oral cavity, preventing it from acting as a pharyngeal articulator.
Despite all this, scholars remain divided as to how "special" the human vocal tract really is. It has been shown that the larynx does descend to some extent during development in chimpanzees, followed by hyoidal descent. As against this, Philip Lieberman points out that only humans have evolved permanent and substantial laryngeal descent in association with hyoidal descent, resulting in a curved tongue and two-tube vocal tract with 1:1 proportions. Uniquely in the human case, simple contact between the epiglottis and velum is no longer possible, disrupting the normal mammalian separation of the respiratory and digestive tracts during swallowing. Since this entails substantial costs — increasing the risk of choking while swallowing food — we are forced to ask what benefits might have outweighed those costs. The obvious benefit — so it is claimed — must have been speech. But this idea has been vigorously contested. One objection is that humans are in fact not seriously at risk of choking on food: medical statistics indicate that accidents of this kind are extremely rare. Another objection is that in the view of most scholars, speech as we know it emerged relatively late in human evolution, roughly contemporaneously with the emergence of Homo sapiens. A development as complex as the reconfiguration of the human vocal tract would have required much more time, implying an early date of origin. This discrepancy in timescales undermines the idea that human vocal flexibility was initially driven by selection pressures for speech.
The size exaggeration hypothesisEdit
To lower the larynx is to increase the length of the vocal tract, in turn lowering formant frequencies so that the voice sounds "deeper" — giving an impression of greater size. John Ohala argues that the function of the lowered larynx in humans, especially males, is probably to enhance threat displays rather than speech itself. Ohala points out that if the lowered larynx were an adaptation for speech, we would expect adult human males to be better adapted in this respect than adult females, whose larynx is considerably less low. In fact, females invariably outperform males in verbal tests, falsifying this whole line of reasoning. W. Tecumseh Fitch likewise argues that this was the original selective advantage of laryngeal lowering in our species. Although (according to Fitch) the initial lowering of the larynx in humans had nothing to do with speech, the increased range of possible formant patterns was subsequently co-opted for speech. Size exaggeration remains the sole function of the extreme laryngeal descent observed in male deer. Consistent with the size exaggeration hypothesis, a second descent of the larynx occurs at puberty in humans, although only in males. In response to the objection that the larynx is descended in human females, Fitch suggests that mothers vocalising to protect their infants would also have benefited from this ability.
Could the Neanderthals speak?Edit
Most specialists credit the Neanderthals with speech abilities not radically different from those of modern Homo sapiens. An indirect line of argument is that their tool-making and hunting tactics would have been difficult to learn or execute without some kind of speech. A recent extraction of DNA from Neanderthal bones indicates that Neanderthals had the same version of the FOXP2 gene as modern humans. This gene, once mistakenly described as the "grammar gene", plays a role in controlling the orofacial movements which (in modern humans) are involved in speech.
During the 1970s, it was widely believed that the Neanderthals lacked modern speech capacities. It was claimed that they possessed a hyoid bone so high up in the vocal tract as to preclude the possibility of producing certain vowel sounds.
The hyoid bone is present in many mammals. It allows a wide range of tongue, pharyngeal and laryngeal movements by bracing these structures alongside each other in order to produce variation. It is now realised that its lowered position is not unique to Homo sapiens, while its relevance to vocal flexibility may have been overstated: although men have a lower larynx, they do not produce a wider range of sounds than women or two-year-old babies. There is no evidence that the larynx position of the Neanderthals impeded the range of vowel sounds they could produce. The discovery of a modern-looking hyoid bone of a Neanderthal man in the Kebara Cave in Israel led its discoverers to argue that the Neanderthals had a descended larynx, and thus human-like speech capabilities. However, other researchers have claimed that the morphology of the hyoid is not indicative of the larynx's position. It is necessary to take into consideration the skull base, the mandible and the cervical vertebrae and a cranial reference plane.
The morphology of the outer and middle ear of Middle Pleistocene hominins from Atapuerca SH in Spain, believed to be proto-Neanderthal, suggests they had an auditory sensitivity similar to modern humans and very different from chimpanzees. They were probably able to differentiate between many different speech sounds.
Hypoglossal nerve, cervical plexus, and their branches
|Anatomical terms of neuroanatomy|
The hypoglossal nerve plays an important role in controlling movements of the tongue. In 1998, one research team used the size of the hypoglossal canal in the base of fossil skulls in an attempt to estimate the relative number of nerve fibres, claiming on this basis that Middle Pleistocene hominins and Neanderthals had more fine-tuned tongue control than either australopithecines or apes. Subsequently, however, it was demonstrated that hypoglossal canal size and nerve sizes are not correlated, and it is now accepted that such evidence is uninformative about the timing of human speech evolution.
Origin of speech soundsEdit
Distinctive features theoryEdit
According to one influential school, the human vocal apparatus is intrinsically digital on the model of a keyboard or digital computer. If so, this is remarkable: nothing about a chimpanzee's vocal apparatus suggests a digital keyboard, notwithstanding the anatomical and physiological similarities. This poses the question as to when and how, during and the course of human evolution, the transition from analog to digital structure and function occurred.
The human supralaryngeal tract is said to be digital in the sense that it is an arrangement of moveable toggles or switches, each of which, at any one time, must be in one state or another. The vocal cords, for example, are either vibrating (producing a sound) or not vibrating (in silent mode). By virtue of simple physics, the corresponding distinctive feature — in this case, "voicing" — cannot be somewhere in between. The options are limited to "off" and "on". Equally digital is the feature known as "nasalisation". At any given moment the soft palate or velum either allows or doesn't allow sound to resonate in the nasal chamber. In the case of lip and tongue positions, more than two digital states may be allowed. (To experiment with this, click on Interactive Saggital Section).
The theory that speech sounds are composite entities constituted by complexes of binary phonetic features was first advanced in 1938 by the Russian linguist Roman Jakobson. A prominent early supporter of this approach was Noam Chomsky, who went on to extend it from phonology to language more generally, in particular to the study of syntax and semantics. In his 1965 book, Aspects of the Theory of Syntax, Chomsky treated semantic concepts as combinations of binary-digital atomic elements explicitly on the model of distinctive features theory. The lexical item "bachelor", on this basis, would be expressed as [+ Human], [+ Male], [- Married].
Supporters of this approach view the vowels and consonants recognised by speakers of a particular language or dialect at a particular time as cultural entities of little scientific interest. From a natural science standpoint, the units which matter are those common to Homo sapiens by virtue of our biological nature. By combining the atomic elements or "features" with which all humans are innately equipped, anyone may in principle generate the entire range of vowels and consonants to be found in any of the world's languages, whether past, present or future. The distinctive features are in this sense atomic components of a universal language.
|Pronounced with the lower lip against the teeth:||[f] (fan)||[v] (van)|
|Pronounced with the tongue against the teeth:||[θ] (thin, thigh)||[ð] (then, thy)|
|Pronounced with the tongue near the gums:||[s] (sip)||[z] (zip)|
|Pronounced with the tongue bunched up:||[ʃ] (pressure)||[ʒ] (pleasure)|
In recent years, the notion of an innate "universal grammar" underlying phonological variation has been called into question. The most comprehensive monograph ever written about speech sounds, Sounds of the World's Languages, by Peter Ladefoged and Ian Maddieson, found virtually no basis for the postulation of some small number of fixed, discrete, universal phonetic features. Examining 305 languages, for example, they encountered vowels that were positioned basically everywhere along the articulatory and acoustic continuum. Ladefoged concludes that phonological features are not determined by human nature: "Phonological features are best regarded as artifacts that linguists have devised in order to describe linguistic systems." The controversy remains unresolved.
Self-organization characterizes systems where macroscopic structures are spontaneously formed out of local interactions between the many components of the system. In self-organized systems, global organizational properties are not to be found at the local level. In colloquial terms, self-organisation is roughly captured by the idea of "bottom-up" (as opposed to "top-down") organisation. Examples of self-organized systems range from ice crystals to galaxy spirals in the inorganic world, and from spots on the leopard skins to the architecture of termite nests or shape of a flock of starlings.
According to many phoneticians, the sounds of language arrange and re-arrange themselves through self-organization Speech sounds have both perceptual ("how you hear them") and articulatory ("how you produce them") properties, all with continuous values. Speakers tend to minimise effort, favouring ease of articulation over clarity. Listeners do the opposite, favouring sounds which are easy to distinguish even if difficult to pronounce. Since speakers and listeners are constantly switching roles, the syllable systems actually found in the world's languages turn out to be a compromise between acoustic distinctiveness on the one hand, and articulatory ease on the other.
How, precisely, do systems of vowels, consonants and syllables arise? Agent-based computer models take the perspective of self-organisation at the level of the speech community or population. The two main paradigms here are (1) the iterated learning model and (2) the language game model. Iterated learning focuses on transmission from generation to generation, typically with just one agent in each generation. In the language game model, a whole population of agents simultaneously produce, perceive and learn language, inventing novel forms when the need arises.
Several models have shown how relatively simple peer-to-peer vocal interactions, such as imitation, can spontaneously self-organize a system of sounds shared by the whole population, and different in different populations. For example, models elaborated by Berrah et al., as well as de Boer, and recently reformulated using Bayesian theory, showed how a group of individuals playing imitation games can self-organize repertoires of vowel sounds which share substantial properties with human vowel systems. For example, in de Boer's model, initially vowels are generated randomly, but agents learn from each other as they interact repeatedly over time. Agent A chooses a vowel from its repertoire and produces it, inevitably with some noise. Agent B hears this vowel and chooses the closest equivalent from its own repertoire. To check whether this truly matches the original, B produces the vowel it thinks it has heard, whereupon A refers once again to its own repertoire to find the closest equivalent. If this matches the one it initially selected, the game is successful, otherwise it has failed. "Through repeated interactions," according to de Boer, "vowel systems emerge that are very much like the ones found in human languages."
In a different model, the phonetician Björn Lindblom was able to predict, on self-organizational grounds, the favoured choices of vowel systems ranging from three to nine vowels on the basis of a principle of optimal perceptual differentiation.
Further models studied the role of self-organization in the origins of phonemic coding and combinatoriality, that is the existence of phonemes and their systematic reuse to build structured syllables. Pierre-Yves Oudeyer developed models which showed that basic neural equipment for adaptive holistic vocal imitation, coupling directly motor and perceptual representations in the brain, can generate spontaneously shared combinatorial systems of vocalizations, including phonotactic patterns, in a society of babbling individuals. These models also characterized how morphological and physiological innate constraints can interact with these self-organized mechanisms to account for both the formation of statistical regularities and diversity in vocalization systems.
The gestural theory states that speech was a relatively late development, evolving by degrees from a system that was originally gestural.
Two types of evidence support this theory:
- Gestural language and vocal language depend on similar neural systems. The regions on the cortex that are responsible for mouth and hand movements border each other.
- Nonhuman primates minimise vocal signals in favour of manual, facial and other visible gestures in order to express simple concepts and communicative intentions in the wild. Some of these gestures resemble those of humans, such as the "begging posture", with the hands stretched out, which humans share with chimpanzees.
Research has found strong support for the idea that spoken language and signing depend on similar neural structures. Patients who used sign language, and who suffered from a left-hemisphere lesion, showed the same disorders with their sign language as vocal patients did with their oral language. Other researchers found that the same left-hemisphere brain regions were active during sign language as during the use of vocal or written language.
Humans spontaneously use hand and facial gestures when formulating ideas to be conveyed in speech. There are also, of course, many sign languages in existence, commonly associated with deaf communities; as noted above, these are equal in complexity, sophistication, and expressive power, to any oral language. The main difference is that the "phonemes" are produced on the outside of the body, articulated with hands, body, and facial expression, rather than inside the body articulated with tongue, teeth, lips, and breathing.
Critics note that for mammals in general, sound turns out to be the best medium in which to encode information for transmission over distances at speed. Given the probability that this applied also to early humans, it's hard to see why they should have abandoned this efficient method in favour of more costly and cumbersome systems of visual gesturing — only to return to sound at a later stage.
By way of explanation, it has been proposed that at a relatively late stage in human evolution, our ancestors' hands became so much in demand for making and using tools that the competing demands of manual gesturing became a hindrance. The transition to spoken language is said to have occurred only at that point. Since humans throughout evolution have been making and using tools, however, most scholars remain unconvinced by this argument. (For a different approach to this puzzle — one setting out from considerations of signal reliability and trust — see "from pantomime to speech" below).
When did speech evolve?Edit
Little is known about the timing of language's emergence in the human species. Unlike writing, speech leaves no material trace, making it archaeologically invisible. Lacking direct linguistic evidence, specialists in human origins have resorted to the study of anatomical features and genes arguably associated with speech production. While such studies may tell us whether pre-modern Homo species had speech capacities, we still don't know whether they actually spoke. While no one doubts that they communicated vocally, the anatomical and genetic data lack the resolution necessary to differentiate proto-language from speech.
Using statistical methods to estimate the time required to achieve the current spread and diversity in modern languages today, Johanna Nichols — a linguist at the University of California, Berkeley — argued in 1998 that vocal languages must have begun diversifying in our species at least 100,000 years ago.
More recently — in 2012 — anthropologists Charles Perreault and Sarah Mathew used phonemic diversity to suggest a date consistent with this. "Phonemic diversity" denotes the number of perceptually distinct units of sound — consonants, vowels and tones — in a language. The current worldwide pattern of phonemic diversity potentially contains the statistical signal of the expansion of modern Homo sapiens out of Africa, beginning around 60-70 thousand years ago. Some scholars argue that phonemic diversity evolves slowly and can be used as a clock to calculate how long the oldest African languages would have to have been around in order to accumulate the number of phonemes they possess today. As human populations left Africa and expanded into the rest of the world, they underwent a series of bottlenecks — points at which only a very small population survived to colonise a new continent or region. Allegedly such population crash led to a corresponding reduction in genetic, phenotypic and phonemic diversity. African languages today have some of the largest phonemic inventories in the world, while the smallest inventories are found in South America and Oceania, some of the last regions of the globe to be colonized. For example, Rotokas, a language of New Guinea, and Pirahã, spoken in South America, both have just 11 phonemes, while !Xun, a language spoken in Southern Africa has 141 phonemes. The authors use a natural experiment — the colonization of mainland Southeast Asia on the one hand, the long-isolated Andaman Islands on the other — to estimate the rate at which phonemic diversity increases through time. Using this rate, they estimate that the world's languages date back to the Middle Stone Age in Africa, sometime between 350 thousand and 150 thousand years ago. This corresponds to the speciation event which gave rise to Homo sapiens.
These and similar studies have however been criticized by linguists who argue that they are based on a flawed analogy between genes and phonemes, since phonemes are frequently transferred laterally between languages unlike genes, and on a flawed sampling of the world's languages, since both Oceania and the Americas also contain languages with very high numbers of phonemes, and Africa contains languages with very few. They argue that the actual distribution of phonemic diversity in the world reflects recent language contact and not deep language history - since it is well demonstrated that languages can lose or gain many phonemes over very short periods. In other words, there is no valid linguistic reason to expect genetic founder effects to influence phonemic diversity.
"I cannot doubt that language owes its origin to the imitation and modification, aided by signs and gestures, of various natural sounds, the voices of other animals, and man's own instinctive cries."— Charles Darwin, 1871. The Descent of Man, and Selection in Relation to Sex.
In 1861, historical linguist Max Müller published a list of speculative theories concerning the origins of spoken language:
- Bow-wow. The bow-wow or cuckoo theory, which Müller attributed to the German philosopher Johann Gottfried Herder, saw early words as imitations of the cries of beasts and birds.
- Pooh-pooh. The Pooh-Pooh theory saw the first words as emotional interjections and exclamations triggered by pain, pleasure, surprise and so on.
- Ding-dong. Müller suggested what he called the Ding-Dong theory, which states that all things have a vibrating natural resonance, echoed somehow by man in his earliest words.
- Yo-he-ho. The yo-he-ho theory saw language emerging out of collective rhythmic labour, the attempt to synchronise muscular effort resulting in sounds such as heave alternating with sounds such as ho.
- Ta-ta. This did not feature in Max Müller's list, having been proposed in 1930 by Sir Richard Paget. According to the ta-ta theory, humans made the earliest words by tongue movements that mimicked manual gestures, rendering them audible.
Most scholars today consider all such theories not so much wrong — they occasionally offer peripheral insights — as comically naïve and irrelevant. The problem with these theories is that they are so narrowly mechanistic. They assume that once our ancestors had stumbled upon the appropriate ingenious mechanism for linking sounds with meanings, language automatically evolved and changed.
Problems of reliability and deceptionEdit
From the perspective of modern science, the main obstacle to the evolution of speech-like communication in nature is not a mechanistic one. Rather, it is that symbols — arbitrary associations of sounds with corresponding meanings — are unreliable and may well be false. As the saying goes, "words are cheap". The problem of reliability was not recognised at all by Darwin, Müller or the other early evolutionist theorists.
Animal vocal signals are for the most part intrinsically reliable. When a cat purrs, the signal constitutes direct evidence of the animal's contented state. One can "trust" the signal not because the cat is inclined to be honest, but because it just can't fake that sound. Primate vocal calls may be slightly more manipulable, but they remain reliable for the same reason — because they are hard to fake. Primate social intelligence is Machiavellian — self-serving and unconstrained by moral scruples. Monkeys and apes often attempt to deceive one another, while at the same time constantly on guard against falling victim to deception themselves. Paradoxically, it is precisely primates' resistance to deception that blocks the evolution of their vocal communication systems along language-like lines. Language is ruled out because the best way to guard against being deceived is to ignore all signals except those that are instantly verifiable. Words automatically fail this test.
Words are easy to fake. Should they turn out to be lies, listeners will adapt by ignoring them in favour of hard-to-fake indices or cues. For language to work, then, listeners must be confident that those with whom they are on speaking terms are generally likely to be honest. A peculiar feature of language is "displaced reference", which means reference to topics outside the currently perceptible situation. This property prevents utterances from being corroborated in the immediate "here" and "now". For this reason, language presupposes relatively high levels of mutual trust in order to become established over time as an evolutionarily stable strategy. A theory of the origins of language must therefore explain why humans could begin trusting cheap signals in ways that other animals apparently cannot (see signalling theory).
The "mother tongues" hypothesis was proposed in 2004 as a possible solution to this problem. W. Tecumseh Fitch suggested that the Darwinian principle of "kin selection" — the convergence of genetic interests between relatives — might be part of the answer. Fitch suggests that spoken languages were originally "mother tongues". If speech evolved initially for communication between mothers and their own biological offspring, extending later to include adult relatives as well, the interests of speakers and listeners would have tended to coincide. Fitch argues that shared genetic interests would have led to sufficient trust and cooperation for intrinsically unreliable vocal signals — spoken words — to become accepted as trustworthy and so begin evolving for the first time.
Critics of this theory point out that kin selection is not unique to humans. Ape mothers also share genes with their offspring, as do all animals, so why is it only humans who speak? Furthermore, it is difficult to believe that early humans restricted linguistic communication to genetic kin: the incest taboo must have forced men and women to interact and communicate with non-kin. So even if we accept Fitch's initial premises, the extension of the posited "mother tongue" networks from relatives to non-relatives remains unexplained.
Ib Ulbæk invokes another standard Darwinian principle — "reciprocal altruism" — to explain the unusually high levels of intentional honesty necessary for language to evolve. 'Reciprocal altruism' can be expressed as the principle that if you scratch my back, I'll scratch yours. In linguistic terms, it would mean that if you speak truthfully to me, I'll speak truthfully to you. Ordinary Darwinian reciprocal altruism, Ulbæk points out, is a relationship established between frequently interacting individuals. For language to prevail across an entire community, however, the necessary reciprocity would have needed to be enforced universally instead of being left to individual choice. Ulbæk concludes that for language to evolve, early society as a whole must have been subject to moral regulation.
Critics point out that this theory fails to explain when, how, why or by whom "obligatory reciprocal altruism" could possibly have been enforced. Various proposals have been offered to remedy this defect. A further criticism is that language doesn't work on the basis of reciprocal altruism anyway. Humans in conversational groups don't withhold information to all except listeners likely to offer valuable information in return. On the contrary, they seem to want to advertise to the world their access to socially relevant information, broadcasting it to anyone who will listen without thought of return.
"Gossip and grooming"Edit
Gossip, according to Robin Dunbar, does for group-living humans what manual grooming does for other primates — it allows individuals to service their relationships and so maintain their alliances. As humans began living in larger and larger social groups, the task of manually grooming all one's friends and acquaintances became so time-consuming as to be unaffordable. In response to this problem, humans invented "a cheap and ultra-efficient form of grooming" — vocal grooming. To keep your allies happy, you now needed only to "groom" them with low-cost vocal sounds, servicing multiple allies simultaneously while keeping both hands free for other tasks. Vocal grooming (the production of pleasing sounds lacking syntax or combinatorial semantics) then evolved somehow into syntactical speech.
Critics of this theory point out that the very efficiency of "vocal grooming" — that words are so cheap — would have undermined its capacity to signal commitment of the kind conveyed by time-consuming and costly manual grooming. A further criticism is that the theory does nothing to explain the crucial transition from vocal grooming — the production of pleasing but meaningless sounds — to the cognitive complexities of syntactical speech.
From pantomime to speechEdit
According to another school of thought, language evolved from mimesis — the "acting out" of scenarios using vocal and gestural pantomime. For as long as utterances needed to be emotionally expressive and convincing, it was not possible to complete the transition to purely conventional signs. On this assumption, pre-linguistic gestures and vocalisations would have been required not just to disambiguate intended meanings, but also to inspire confidence in their intrinsic reliability. If contractual commitments were necessary in order to inspire community-wide trust in communicative intentions, it would follow that these had to be in place before humans could shift at last to an ultra-efficient, high-speed — digital as opposed to analog — signalling format. Vocal distinctive features (sound contrasts) are ideal for this purpose. It is therefore suggested that the establishment of contractual understandings enabled the decisive transition from mimetic gesture to fully conventionalised, digitally encoded speech.
The ritual/speech coevolution theory was originally proposed by the distinguished social anthropologist Roy Rappaport before being elaborated by anthropologists such as Chris Knight, Jerome Lewis, Nick Enfield, Camilla Power and Ian Watts. Cognitive scientist and robotics engineer Luc Steels is another prominent supporter of this general approach, as is biological anthropologist/neuroscientist Terrence Deacon.
These scholars argue that there can be no such thing as a "theory of the origins of language". This is because language is not a separate adaptation but an internal aspect of something much wider — namely, human symbolic culture as a whole. Attempts to explain language independently of this wider context have spectacularly failed, say these scientists, because they are addressing a problem with no solution. Can we imagine a historian attempting to explain the emergence of credit cards independently of the wider system of which they are a part? Using a credit card makes sense only if you have a bank account institutionally recognised within a certain kind of advanced capitalist society — one where communications technology has already been invented and fraud can be detected and prevented. In much the same way, language would not work outside a specific array of social mechanisms and institutions. For example, it would not work for an ape communicating with other apes in the wild. Not even the cleverest ape could make language work under such conditions.
"Lie and alternative, inherent in language, ... pose problems to any society whose structure is founded on language, which is to say all human societies. I have therefore argued that if there are to be words at all it is necessary to establish The Word, and that The Word is established by the invariance of liturgy."
Advocates of this school of thought point out that words are cheap. As digital hallucinations, they are intrinsically unreliable. Should an especially clever ape, or even a group of articulate apes, try to use words in the wild, they would carry no conviction. The primate vocalisations that do carry conviction — those they actually use — are unlike words, in that they are emotionally expressive, intrinsically meaningful and reliable because they are relatively costly and hard to fake.
Speech consists of digital contrasts whose cost is essentially zero. As pure social conventions, signals of this kind cannot evolve in a Darwinian social world — they are a theoretical impossibility. Being intrinsically unreliable, language works only if you can build up a reputation for trustworthiness within a certain kind of society — namely, one where symbolic cultural facts (sometimes called "institutional facts") can be established and maintained through collective social endorsement. In any hunter-gatherer society, the basic mechanism for establishing trust in symbolic cultural facts is collective ritual. Therefore, the task facing researchers into the origins of language is more multidisciplinary than is usually supposed. It involves addressing the evolutionary emergence of human symbolic culture as a whole, with language an important but subsidiary component.
Critics of the theory include Noam Chomsky, who terms it the "non-existence" hypothesis — a denial of the very existence of language as an object of study for natural science. Chomsky's own theory is that language emerged in an instant and in perfect form, prompting his critics in turn to retort that only something that doesn't exist — a theoretical construct or convenient scientific fiction — could possibly emerge in such a miraculous way. The controversy remains unresolved.
Twentieth century speculationsEdit
The essay "The festal origin of human speech", though published in the late nineteenth century, made little impact until the American philosopher Susanne Langer re-discovered and publicised it in 1941.
"In the early history of articulate sounds they could make no meaning themselves, but they preserved and got intimately associated with the peculiar feelings and perceptions that came most prominently into the minds of the festal players during their excitement."— J. Donovan, 1891. The Festal Origin of Human Speech.
The theory sets out from the observation that primate vocal sounds are above all emotionally expressive. The emotions aroused are socially contagious. Because of this, an extended bout of screams, hoots or barks will tend to express not just the feelings of this or that individual but the mutually contagious ups and downs of everyone within earshot.
Turning to the ancestors of Homo sapiens, the "festal origin" theory suggests that in the "play-excitement" preceding or following a communal hunt or other group activity, everyone might have combined their voices in a comparable way, emphasising their mood of togetherness with such noises as rhythmic drumming and hand-clapping. Variably pitched voices would have formed conventional patterns, such that choral singing became an integral part of communal celebration.
Although this was not yet speech, according to Langer, it developed the vocal capacities from which speech would later derive. There would be conventional modes of ululating, clapping or dancing appropriate to different festive occasions, each so intimately associated with that kind of occasion that it would tend to collectively uphold and embody the concept of it. Anyone hearing a snatch of sound from such a song would recall the associated occasion and mood. A melodic, rhythmic sequence of syllables conventionally associated with a certain type of celebration would become, in effect, its vocal mark. On that basis, certain familiar sound sequences would become "symbolic".
In support of all this, Langer cites ethnographic reports of tribal songs consisting entirely of "rhythmic nonsense syllables". She concedes that an English equivalent such as "hey-nonny-nonny", although perhaps suggestive of certain feelings or ideas, is neither noun, verb, adjective, nor any other syntactical part of speech. So long as articulate sound served only in the capacity of "hey nonny-nonny", "hallelujah" or "alack-a-day", it cannot yet have been speech. For that to arise, according to Langer, it was necessary for such sequences to be emitted increasingly out of context — outside the total situation that gave rise to them. Extending a set of associations from one cognitive context to another, completely different one, is the secret of metaphor. Langer invokes an early version of what is nowadays termed "grammaticalisation" theory to show how, from, such a point of departure, syntactically complex speech might progressively have arisen.
Langer acknowledges Emile Durkheim as having proposed a strikingly similar theory back in 1912. For recent thinking along broadly similar lines, see Steven Brown on "musilanguage", Chris Knight on "ritual" and "play", Jerome Lewis on "mimicry", Steven Mithen on "Hmmmmm" Bruce Richman on "nonsense syllables" and Alison Wray on "holistic protolanguage".
The term "musilanguage" (or "hmmmmm") refers to a pre-linguistic system of vocal communication from which (according to some scholars) both music and language later derived. The idea is that rhythmic, melodic, emotionally expressive vocal ritual helped bond coalitions and, over time, set up selection pressures for enhanced volitional control over the speech articulators. Patterns of synchronised choral chanting are imagined to have varied according to the occasion. For example, "we're setting off to find honey" might sound qualitatively different from "we're setting off to hunt" or "we're grieving over our relative's death". If social standing depended on maintaining a regular beat and harmonising one's own voice with that of everyone else, group members would have come under pressure to demonstrate their choral skills.
Archaeologist Steven Mithen speculates that the Neanderthals possessed some such system, expressing themselves in a "language" known as "Hmmmmm", standing for Holistic, manipulative, multi-modal, musical and mimetic.p. 169-175 In Bruce Richman's earlier version of essentially the same idea, frequent repetition of the same few songs by many voices made it easy for people to remember those sequences as whole units. Activities that a group of people were doing while they were vocalising together — activities that were important or striking or richly emotional — came to be associated with particular sound sequences, so that each time a fragment was heard, it evoked highly specific memories. The idea is that the earliest lexical items (words) started out as abbreviated fragments of what were originally communal songs.
"Whenever people sang or chanted a particular sound sequence they would remember the concrete particulars of the situation most strongly associated with it: ah, yes! we sing this during this particular ritual admitting new members to the group; or, we chant this during a long journey in the forest; or, when a clearing is finished for a new camp, this is what we chant; or these are the keenings we sing during ceremonies over dead members of our group."— Richman, B. 2000. How music fixed "nonsense" into significant formulas: on rhythm, repetition, and meaning. In N. L. Wallin, B. Merker and S. Brown (eds), The Origins of Music: An introduction to evolutionary musicology. Cambridge, Massachusetts: MIT Press, pp. 301-314.
As group members accumulated an expanding repertoire of songs for different occasions, interpersonal call-and-response patterns evolved along one trajectory to assume linguistic form. Meanwhile, along a divergent trajectory, polyphonic singing and other kinds of music became increasingly specialised and sophisticated.
To explain the establishment of syntactical speech, Richman cites English "I wanna go home". He imagines this to have been learned in the first instance not as a combinatorial sequence of free-standing words, but as a single stuck-together combination — the melodic sound people make to express "feeling homesick". Someone might sing "I wanna go home", prompting other voices to chime in with "I need to go home", "I'd love to go home", "Let's go home" and so forth. Note that one part of the song remains constant, while another is permitted to vary. If this theory is accepted, syntactically complex speech began evolving as each chanted mantra allowed for variation at a certain point, allowing for the insertion of an element from some other song. For example, while mourning during a funeral rite, someone might want to recall a memory of collecting honey with the deceased, signalling this at an appropriate moment with a fragment of the "we're collecting honey" song. Imagine that such practices became common. Meaning-laden utterances would now have become subject to a distinctively linguistic creative principle — that of recursive embedding.
Many scholars associate the evolutionary emergence of speech with profound social, sexual, political and cultural developments. One view is that primate-style dominance needed to give way to a more cooperative and egalitarian lifestyle of the kind characteristic of modern hunter-gatherers.
According to Michael Tomasello, the key cognitive capacity distinguishing Homo sapiens from our ape cousins is "intersubjectivity". This entails turn-taking and role-reversal: your partner strives to read your mind, you simultaneously strive to read theirs, and each of you makes a conscious effort to assist the other in the process. The outcome is that each partner forms a representation of the other's mind in which their own can be discerned by reflection.
Tomasello argues that this kind of bi-directional cognition is central to the very possibility of linguistic communication. Drawing on his research with both children and chimpanzees, he reports that human infants, from one year old onwards, begin viewing their own mind as if from the standpoint of others. He describes this as a cognitive revolution. Chimpanzees, as they grow up, never undergo such a revolution. The explanation, according to Tomasello, is that their evolved psychology is adapted to a deeply competitive way of life. Wild-living chimpanzees form despotic social hierarchies, most interactions involving calculations of dominance and submission. An adult chimp will strive to outwit its rivals by guessing at their intentions while blocking them from reciprocating. Since bi-directional intersubjective communication is impossible under such conditions, the cognitive capacities necessary for language don't evolve.
In the scenario favoured by David Erdal and Andrew Whiten, primate-style dominance provoked equal and opposite coalitionary resistance — counter-dominance. During the course of human evolution, increasingly effective strategies of rebellion against dominant individuals led to a compromise. While abandoning any attempt to dominate others, group members vigorously asserted their personal autonomy, maintaining their alliances to make potentially dominant individuals think twice. Within increasingly stable coalitions, according to this perspective, status began to be earned in novel ways, social rewards accruing to those perceived by their peers as especially cooperative and self-aware.
While counter-dominance, according to this evolutionary narrative, culminates in a stalemate, anthropologist Christopher Boehm extends the logic a step further. Counter-dominance tips over at last into full-scale "reverse dominance". The rebellious coalition decisively overthrows the figure of the primate alpha-male. No dominance is allowed except that of the self-organised community as a whole.
As a result of this social and political change, hunter-gatherer egalitarianism is established. As children grow up, they are motivated by those around them to reverse perspective, engaging with other minds on the model of their own. Selection pressures favour such psychological innovations as imaginative empathy, joint attention, moral judgment, project-oriented collaboration and the ability to evaluate one's own behaviour from the standpoint of others. Underpinning enhanced probabilities of cultural transmission and cumulative cultural evolution, these developments culminate in the establishment of hunter-gatherer-style egalitarianism in association with intersubjective communication and cognition. It is in this social and political context that language evolves.
Scenarios involving mother-infant interactionsEdit
"Putting the baby down"Edit
According to Dean Falk's "putting the baby down" theory, vocal interactions between early hominin mothers and infants sparked a sequence of events that led, eventually, to our ancestors' earliest words. The basic idea is that evolving human mothers, unlike their monkey and ape counterparts, couldn't move around and forage with their infants clinging onto their backs. Loss of fur in the human case left infants with no means of clinging on. Frequently, therefore, mothers had to put their babies down. As a result, these babies needed reassurance that they were not being abandoned. Mothers responded by developing "motherese" — an infant-directed communicative system embracing facial expressions, body language, touching, patting, caressing, laughter, tickling and emotionally expressive contact calls. The argument is that language somehow developed out of all this.
While this theory may explain a certain kind of infant-directed "protolanguage" — known today as "motherese" — it does little to solve the really difficult problem, which is the emergence among adults of syntactical speech.
Evolutionary anthropologist Sarah Hrdy observes that only human mothers among great apes are willing to let another individual take hold of their own babies; further, we are routinely willing to let others babysit. She identifies lack of trust as the major factor preventing chimp, bonobo or gorilla mothers from doing the same: "If ape mothers insist on carrying their babies everywhere ... it is because the available alternatives are not safe enough." The fundamental problem is that ape mothers (unlike monkey mothers who may often babysit) do not have female relatives nearby. The strong implication is that, in the course of Homo evolution, allocare could develop because Homo mothers did have female kin close by — in the first place, most reliably, their own mothers. Extending the Grandmother hypothesis, Hrdy argues that evolving Homo erectus females necessarily relied on female kin initially; this novel situation in ape evolution of mother, infant and mother's mother as allocarer provided the evolutionary ground for the emergence of intersubjectivity. She relates this onset of "cooperative breeding in an ape" to shifts in life history and slower child development, linked to the change in brain and body size from the 2 million year mark.
Primatologist Klaus Zuberbühler uses these ideas to help explain the emergence of vocal flexibility in the human species. Co-operative breeding would have compelled infants to struggle actively to gain the attention of caregivers, not all of whom would have been directly related. A basic primate repertoire of vocal signals may have been insufficient for this social challenge. Natural selection, according to this view, would have favoured babies with advanced vocal skills, beginning with babbling (which triggers positive responses in care-givers) and paving the way for the elaborate and unique speech abilities of modern humans.
Was "mama" the first word?Edit
These ideas might be linked to those of the renowned structural linguist Roman Jakobson, who claimed that "the sucking activities of the child are accompanied by a slight nasal murmur, the only phonation to be produced when the lips are pressed to the mother's breast ... and the mouth is full". He proposed that later in the infant's development, "this phonatory reaction to nursing is reproduced as an anticipatory signal at the mere sight of food and finally as a manifestation of a desire to eat, or more generally, as an expression of discontent and impatient longing for missing food or absent nurser, and any ungranted wish." So, the action of opening and shutting the mouth, combined with the production of a nasal sound when the lips are closed, yielded the sound sequence "Mama", which may therefore count as the very first word. Peter MacNeilage sympathetically discusses this theory in his major book, The Origin of Speech, linking it with Dean Falk's "putting the baby down" theory (see above). Needless to say, other scholars have suggested completely different candidates for Homo sapiens' very first word.
Niche construction theoryEdit
While the biological language faculty is genetically inherited, actual languages or dialects are culturally transmitted, as are social norms, technological traditions and so forth. Biologists expect a robust co-evolutionary trajectory linking human genetic evolution with the evolution of culture. Individuals capable of rudimentary forms of protolanguage would have enjoyed enhanced access to cultural understandings, while these, conveyed in ways that young brains could readily learn, would in turn have become transmitted with increasing efficiency.
In some ways like beavers as they construct their dams, humans have always engaged in niche construction, creating novel environments to which they subsequently become adapted. Selection pressures associated with prior niches tend to become relaxed as humans depend increasingly on novel environments created continuously by their own productive activities. According to Steven Pinker, language is an adaptation to "the cognitive niche". Variations on the theme of ritual/speech co-evolution — according to which speech evolved for purposes of internal communication within a ritually constructed domain — have attempted to specify more precisely when, why and how this special niche was created by human collaborative activity.
"Consider a knight in chess. Is the piece by itself an element of the game? Certainly not. For as a material object, separated from its square on the board and the other conditions of play, it is of no significance for the player. It becomes a real, concrete element only when it takes on or becomes identified with its value in the game. Suppose that during a game this piece gets destroyed or lost. Can it be replaced? Of course it can. Not only by some other knight, but even by an object of quite a different shape, which can be counted as a knight, provided it is assigned the same value as the missing piece."— Saussure, F. de 1983 . Course in General Linguistics. Translated by R. Harris. London: Duckworth, pp. 108-09.
The Swiss scholar Ferdinand de Saussure founded linguistics as a twentieth-century professional discipline. Saussure regarded a language as a rule-governed system, much like a board game such as chess. In order to understand chess, he insisted, we must ignore such external factors as the weather prevailing during a particular session or the material composition of this or that piece. The game is autonomous with respect to its material embodiments. In the same way, when studying language, it's essential to focus on its internal structure as a social institution. External matters (e.g., the shape of the human tongue) are irrelevant from this standpoint. Saussure regarded 'speaking' (parole) as individual, ancillary and more or less accidental by comparison with "language" (langue), which he viewed as collective, systematic and essential.
Saussure showed little interest in Darwin's theory of evolution by natural selection. Nor did he consider it worthwhile to speculate about how language might originally have evolved. Saussure's assumptions in fact cast doubt on the validity of narrowly conceived origins scenarios. His structuralist paradigm, when accepted in its original form, turns scholarly attention to a wider problem: how our species acquired the capacity to establish social institutions in general.
"The basic processes and relations which give verbal behaviour its special characteristics are now fairly well understood. Much of the experimental work responsible for this advance has been carried out on other species, but the results have proved to be surprisingly free of species restrictions. Recent work has shown that the methods can be extended to human behaviour without serious modification."— Skinner, B.F. 1957. Verbal Behavior. New York: Appleton Century Crofts, p. 3.
In the United States, prior to and immediately following World War II, the dominant psychological paradigm was behaviourism. Within this conceptual framework, language was seen as a certain kind of behaviour — namely, verbal behaviour, to be studied much like any other kind of behaviour in the animal world. Rather as a laboratory rat learns how to find its way through an artificial maze, so a human child learns the verbal behaviour of the society into which it is born. The phonological, grammatical and other complexities of speech are in this sense "external" phenomena, inscribed into an initially unstructured brain. Language's emergence in Homo sapiens, from this perspective, presents no special theoretical challenge. Human behaviour, whether verbal or otherwise, illustrates the malleable nature of the mammalian — and especially the human — brain.
"There is a long history of study of origin of language, asking how it arose from calls of apes and so forth. That investigation in my view is a complete waste of time, because language is based on an entirely different principle than any animal communication system."— Chomsky, N., 1988. Language and Problems of Knowledge. Cambridge, Massachusetts: MIT Press, p. 183.
From the mid-1950s onwards, Noam Chomsky, Jerry Fodor and others mounted what they conceptualised as a 'revolution' against behaviourism. Retrospectively, this became labelled 'the cognitive revolution'. Whereas behaviourism had denied the scientific validity of the concept of "mind", Chomsky replied that, in fact, the concept of "body" is more problematic. Behaviourists tended to view the child's brain as a tabula rasa, initially lacking structure or cognitive content. According to B. F. Skinner, for example, richness of behavioural detail (whether verbal or non-verbal) emanated from the environment. Chomsky turned this idea on its head. The linguistic environment encountered by a young child, according to Chomsky's version of psychological nativism, is in fact hopelessly inadequate. No child could possibly acquire the complexities of grammar from such an impoverished source. Far from viewing language as wholly external, Chomsky re-conceptualised it as wholly internal. To explain how a child so rapidly and effortlessly acquires its natal language, he insisted, we must conclude that it comes into the world with the essentials of grammar already pre-installed. No other species, according to Chomsky, is genetically equipped with a language faculty — or indeed with anything remotely like one. The emergence of such a faculty in Homo sapiens, from this standpoint, presents biological science with a major theoretical challenge.
Speech act theoryEdit
Speech acts, according to this body of theory, can be analysed on three different levels: locutionary, illocutionary and perlocutionary. An act is locutionary when viewed as the production of certain linguistic sounds — for example, practicing correct pronunciation in a foreign language. An act is illocutionary insofar as it constitutes an intervention in the world as jointly perceived or understood. Promising, marrying, divorcing, declaring, stating, authorising, announcing and so forth are all speech acts in this illocutionary sense. An act is perlocutionary when viewed in terms of its direct psychological effect on an audience. Frightening a baby by saying 'Boo!' would be an example of a "perlocutionary" act.
For Austin, "doing things" with words means, first and foremost, deploying illocutionary force. The secret of this is community participation or collusion. There must be a 'correct' (conventionally agreed) procedure, and all those concerned must accept that it has been properly followed.
"One of our examples was, for instance, the utterance 'I do' (take this woman to be my lawful wedded wife), as uttered in the course of a marriage ceremony. Here we should say that in saying these words we are doing something — namely, marrying, rather than reporting something, namely that we are marrying."— Austin, J. L. 1962. How To Do Things With Words. Oxford: Oxford University Press, pp. 12-13.
In the case of a priest declaring a couple to be man and wife, his words will have illocutionary force only if he is properly authorised and only if the ceremony is properly conducted, using words deemed appropriate to the occasion. Austin points out that should anyone attempt to baptize a penguin, the act would be null and void. For reasons which have nothing to do with physics, chemistry or biology, baptism is inappropriate to be applied to penguins, irrespective of the verbal formulation used.
This body of theory may have implications for speculative scenarios concerning the origins of speech. "Doing things with words" presupposes shared understandings and agreements pertaining not just to language but to social conduct more generally. Apes might produce sequences of structured sound, influencing one another in that way. To deploy illocutionary force, however, they would need to have entered a non-physical and non-biological realm — one of shared contractual and other intangibles. This novel cognitive domain consists of what philosophers term "institutional facts" — objective facts whose existence, paradoxically, depends on communal faith or belief. Few primatologists, evolutionary psychologists or anthropologists consider that nonhuman primates are capable of the necessary levels of joint attention, sustained commitment or collaboration in pursuit of future goals.
"the deciphering of the genetic code has revealed our possession of a language much older than hieroglyphics, a language as old as life itself, a language that is the most living language of all — even if its letters are invisible and its words are buried in the cells of our bodies."— Beadle, G. and M. Beadle, 1966. The Language of Life. An introduction to the science of genetics. Doubleday and Co, New York.
Biosemiotics is a relatively new discipline, inspired in large part by the discovery of the genetic code in the early 1960s. Its basic assumption is that Homo sapiens is not alone in its reliance on codes and signs. Language and symbolic culture must have biological roots, hence semiotic principles must apply also in the animal world.
The discovery of the molecular structure of DNA apparently contradicted the idea that life could be explained, ultimately, in terms of the fundamental laws of physics. The letters of the genetic alphabet seemed to have "meaning", yet meaning is not a concept which has any place in physics. The natural science community initially solved this difficulty by invoking the concept of "information", treating information as independent of meaning. But a different solution to the puzzle was to recall that the laws of physics in themselves are never sufficient to explain natural phenomena. To explain, say, the unique physical and chemical characteristics of the planets in our solar system, scientists must work out how the laws of physics became constrained by particular sequences of events following the formation of the Sun.
According to Howard Pattee — a pioneering figure in biosemiotics — the same principle applies to the evolution of life on earth, a process in which certain "frozen accidents" or "natural constraints" have from time to time drastically reduced the number of possible evolutionary outcomes. Codes, when they prove to be stable over evolutionary time, are constraints of this kind. The most fundamental such "frozen accident" was the emergence of DNA as a self-replicating molecule, but the history of life on earth has been characterised by a succession of comparably dramatic events, each of which can be conceptualised as the emergence of a new code. From this perspective, the evolutionary emergence of spoken language was one more event of essentially the same kind.
The Handicap principleEdit
In 1975, the Israeli theoretical biologist Amotz Zahavi proposed a novel theory which, although controversial, has come to dominate Darwinian thinking on how signals evolve. Zahavi's "handicap principle" states that to be effective, signals must be reliable; to be reliable, the bodily investment in them must be so high as to make cheating unprofitable.
Paradoxically, if this logic is accepted, signals in nature evolve not to be efficient but, on the contrary, to be elaborate and wasteful of time and energy. A peacock's tail is the classic illustration. Zahavi's theory is that since peahens are on the look-out for male braggarts and cheats, they insist on a display of quality so costly that only a genuinely fit peacock could afford to pay. Needless to say, not all signals in the animal world are quite as elaborate as a peacock's tail. But if Zahavi is correct, all require some bodily investment — an expenditure of time and energy which "handicaps" the signaller in some way.
Animal vocalisations (according to Zahavi) are reliable because they are faithful reflections of the state of the signaller's body. To switch from an honest to a deceitful call, the animal would have to adopt a different bodily posture. Since every bodily action has its own optimal starting position, changing that position to produce a false message would interfere with the task of carrying out the action really intended. The gains made by cheating would not make up for the losses incurred by assuming an improper posture — and so the phony message turns out to be not worth its price.p. 69 This may explain, in particular, why ape and monkey vocal signals have evolved to be so strikingly inflexible when compared with the varied speech sounds produced by the human tongue. The apparent inflexibility of chimpanzee vocalisations may strike the human observer as surprising until we realise that being inflexible is necessarily bound up with being perceptibly honest in the sense of "hard-to-fake".
If we accept this theory, the emergence of speech becomes theoretically impossible. Communication of this kind just cannot evolve. The problem is that words are cheap. Nothing about their acoustic features can reassure listeners that they are genuine and not fakes. Any strategy of reliance on someone else's tongue — perhaps the most flexible organ in the body — presupposes unprecedented levels of honesty and trust. To date, Darwinian thinkers have found it difficult to explain the requisite levels of community-wide cooperation and trust.
An influential standard textbook is Animal Signals, by John Maynard Smith and David Harper. These authors divide the costs of communication into two components, (1) the investment necessary to ensure transmission of a discernible signal; (2) the investment necessary to guarantee that each signal is reliable and not a fake. The authors point out that although costs in the second category may be relatively low, they are not zero. Even in relatively relaxed, cooperative social contexts — for example, when communication is occurring between genetic kin — some investment must be made to guarantee reliability. In short, the notion of super-efficient communication — eliminating all costs except those necessary for successful transmission — is biologically unrealistic. Yet speech comes precisely into this category.
Cognitive linguistics views linguistic structure as arising continuously out of usage. Speakers are forever discovering new ways to convey meanings by producing sounds, and in some cases these novel strategies become conventionalised. Between phonological structure and semantic structure there is no causal relationship. Instead, each novel pairing of sound and meaning involves an imaginative leap.
In their book, Metaphors We Live By, George Lakoff and Mark Johnson helped pioneer this approach, claiming that metaphor is what makes human thought special. All language, they argued, is permeated with metaphor, whose use in fact constitutes distinctively human — that is, distinctively abstract — thought. To conceptualise things which cannot be directly perceived — intangibles such as time, life, reason, mind, society or justice — we have no choice but to set out from more concrete and directly perceptible phenomena such as motion, location, distance, size and so forth. In all cultures across the world, according to Lakoff and Johnson, people resort to such familiar metaphors as ideas are locations, thinking is moving and mind is body. For example, we might express the idea of "arriving at a crucial point in our argument" by proceeding as if literally travelling from one physical location to the next.
Metaphors, by definition, are not literally true. Strictly speaking, they are fictions — from a pedantic standpoint, even falsehoods. But if we couldn't resort to metaphorical fictions, it's doubtful whether we could even form conceptual representations of such nebulous phenomena as "ideas", thoughts", "minds", and so forth.
The bearing of these ideas on current thinking on speech origins remains unclear. One suggestion is that ape communication tends to resist metaphor for social reasons. Since they inhabit a Darwinian (as opposed to morally regulated) social world, these animals are under strong competitive pressure not to accept patent fictions as valid communicative currency. Ape vocal communication tends to be inflexible, marginalising the ultra-flexible tongue, precisely because listeners treat with suspicion any signal which might prove to be a fake. Such insistence on perceptible veracity is clearly incompatible with metaphoric usage. An implication is that neither articulate speech nor distinctively human abstract thought could have begun evolving until our ancestors had become more cooperative and trusting of one another's communicative intentions.
When people converse with one another, according to the American philosopher John Searle, they're making moves, not in the real world which other species inhabit, but in a shared virtual realm peculiar to ourselves. Unlike the deployment of muscular effort to move a physical object, the deployment of illocutionary force requires no physical effort (except movement of the tongue/mouth to produce speech) and produces no effect which any measuring device could detect. Instead, our action takes place on a quite different level — that of social reality. This kind of reality is in one sense hallucinatory, being a product of collective intentionality. It consists, not of "brute facts" — facts which exist anyway, irrespective of anyone's belief — but of "institutional facts", which "exist" only if you believe in them. Government, marriage, citizenship and money are examples of "institutional facts". One can distinguish between "brute" facts and "institutional" ones by applying a simple test. Suppose no one believed in the fact — would it still be true? If the answer is "yes", it's "brute". If the answer is "no", it's "institutional".
"Imagine a group of primitive creatures, more or less like ourselves ... Now imagine that, acting as a group, they build a barrier, a wall around the place where they live ... The wall is designed to keep intruders out and keep members of the group in ... Let us suppose that the wall gradually decays. It slowly deteriorates until all that is left is a line of stones. But let us suppose that the inhabitants continue to treat the line of stones as if it could perform the function of the wall. Let us suppose that, as a matter of fact, they treat the line of stones just as if they understood that it was not to be crossed ... This shift is the decisive move in the creation of institutional reality. It is nothing less than the decisive move in the creation of what we think of as distinctive in human, as opposed to animal, societies."— John R. Searle, 1995. The construction of social reality, Free Press, pp.134
The facts of language in general and of speech in particular are, from this perspective, "institutional" rather than "brute". The semantic meaning of a word, for example, is whatever its users imagine it to be. To "do things with words" is to operate in a virtual world which seems real because we share it in common. In this incorporeal world, the laws of physics, chemistry and biology do not apply. That explains why illocutionary force can be deployed without exerting muscular effort. Apes and monkeys inhabit the "brute" world. To make an impact, they must scream, bark, threaten, seduce or in other ways invest bodily effort. If they were invited to play chess, they would be unable to resist throwing their pieces at one another. Speech is not like that. A few movements of the tongue, under appropriate conditions, can be sufficient to open parliament, annul a marriage, confer a knighthood or declare war. To explain, on a Darwinian basis, how such apparent magic first began to work, we must ask how, when and why Homo sapiens succeeded in establishing the wider domain of institutional facts.
Nature or society?Edit
"Brute facts", in the terminology of speech act philosopher John Searle, are facts which are true anyway, regardless of human belief. Suppose you don't believe in gravity: jump over a cliff and you'll still fall. Natural science is the study of facts of this kind. "Institutional facts" are fictions accorded factual status within human social institutions. Monetary and commercial facts are fictions of this kind. The complexities of today's global currency system are facts only while we believe in them: suspend the belief and the facts correspondingly dissolve. Yet although institutional facts rest on human belief, that doesn't make them mere distortions or hallucinations. Take my confidence that these two five-pound banknotes in my pocket are worth ten pounds. That's not merely my subjective belief: it's an objective, indisputable fact. But now imagine a collapse of public confidence in the currency system. Suddenly, the realities in my pocket dissolve.
Scholars who doubt the scientific validity of the notion of "institutional facts" include Noam Chomsky, for whom language is not social. In Chomsky's view, language is a natural object (a component of the individual brain) and its study, therefore, a branch of natural science. In explaining the origin of language, scholars in this intellectual camp invoke non-social developments — in Chomsky's case, a random genetic mutation. Chomsky argues that language might exist inside the brain of a single mutant gorilla even if no one else believed in it, even if no one else existed apart from the mutant — and even if the gorilla in question remained unaware of its existence, never actually speaking. In the opposite philosophical camp are those who, in the tradition of Ferdinand de Saussure, argue that if no one believed in words or rules, they simply would not exist. These scholars, correspondingly, regard language as essentially institutional, concluding that linguistics should be considered a topic within social science. In explaining the evolutionary emergence of language, scholars in this intellectual camp tend to invoke profound changes in social relationships.
Criticism. Darwinian scientists today see little value in the traditional distinction between "natural" and "social" science. Darwinism in its modern form is the study of cooperation and competition in nature — a topic which is intrinsically social. Against this background, there is an increasing awareness among evolutionary linguists and Darwinian anthropologists that traditional inter-disciplinary barriers can have damaging consequences for investigations into the origins of speech.
- Animal communication
- Deception in animals
- Evolutionary anthropology
- Evolutionary linguistics
- Essay on the Origin of Languages
- Human evolution
- Language acquisition
- Linguistic anthropology
- Linguistic universals
- Neurobiological origins of language
- Origins of society
- Origin of language
- Physical anthropology
- Proto-Human language
- Recent African origin of modern humans
- Signalling theory
- Social evolution
- Sociocultural evolution
- Symbolic culture
- Universal grammar
- Hockett, Charles F. (1960). "The Origin of Speech" (PDF). Scientific American. 203 (3): 88–96. doi:10.1038/scientificamerican0960-88.
- Corballis, Michael C. (2002). From hand to mouth : the origins of language. Princeton: Princeton University Press. ISBN 978-0-691-08803-7. OCLC 469431753.
- Lieberman, Philip (1984). The biology and evolution of language. Cambridge, Massachusetts: Harvard University Press. ISBN 9780674074132. OCLC 10071298.
- Lieberman, Philip (2000). Human language and our reptilian brain : the subcortical bases of speech, syntax, and thought. Cambridge, Massachusetts: Harvard University Press. ISBN 9780674002265. OCLC 43207451.
- Abry, Christian; Boë, Louis-Jean; Laboissière, Rafael; Schwartz, Jean-Luc (1998). "A new puzzle for the evolution of speech?". Behavioral and Brain Sciences. 21 (4): 512–513. doi:10.1017/S0140525X98231268.
- Kelemen, G. (1963). Comparative anatomy and performance of the vocal organ in vertebrates. In R. Busnel (ed.), Acoustic behavior of animals. Amsterdam: Elsevier, pp. 489–521.
- Riede, T.; Bronson, E.; Hatzikirou, H.; Zuberbühler, K. (Jan 2005). "Vocal production mechanisms in a non-human primate: morphological data and a model". J Hum Evol. 48 (1): 85–96. doi:10.1016/j.jhevol.2004.10.002. PMID 15656937.
- Riede, T.; Bronson, E.; Hatzikirou, H.; Zuberbühler, K. (2006). "Multiple discontinuities in nonhuman vocal tracts — A reply". Journal of Human Evolution. 50 (2): 222–225. doi:10.1016/j.jhevol.2005.10.005.
- Fitch, WT. (Jul 2000). "The evolution of speech: a comparative review" (PDF). Trends in Cognitive Science. 4 (7): 258–267. doi:10.1016/S1364-6613(00)01494-7. PMID 10859570.
- Stokoe, W. C. 1960. Sign language structure: an outline of the communicative systems of the American deaf. Silver Spring, MD: Linstock Press.
- Bellugi, U. and E. S. Klima 1975. Aspects of sign language and its structure. In J. F. Kavanagh and J. E. Cutting (eds), The Role of Speech in Language. Cambridge, Massachusetts: The MIT Press, pp. 171 203.
- Hickok, G.; Bellugi, U.; Klima, ES. (Jun 1996). "The neurobiology of sign language and its implications for the neural basis of language". Nature. 381 (6584): 699–702. doi:10.1038/381699a0. PMID 8649515.
- Kegl, Judy; Senghas, Ann; Coppola, Marie (1999). Michel DeGraff, eds. Creation through Contact: Sign Language Emergence and Sign Language Change in Nicaragua / Judy Kegl, Ann Senghas, Marie Coppola. Language creation and language change : creolization, diachrony, and development. Cambridge, Massachusetts: MIT Press. ISBN 978-0-262-04168-3. OCLC 39508250.
- Hauser, MD.; Chomsky, N.; Fitch, WT. (Nov 2002). "The faculty of language: what is it, who has it, and how did it evolve?" (PDF). Science. 298 (5598): 1569–79. doi:10.1126/science.298.5598.1569. PMID 12446899. Archived from the original (PDF) on 2013-12-28.
- Goodall, Jane (1986). The chimpanzees of Gombe : patterns of behavior. Cambridge, Massachusetts: Belknap Press of Harvard University Press. ISBN 978-0-674-11649-8. OCLC 12550961.
- Burling, R (1993). "Primate calls, human language, and nonverbal communication". Current Anthropology. 34: 25–53. doi:10.1086/204132.
- Darwin. C. 1872. The Expression of the Emotions in Man and Animals. London: Murray.
- Ekman, P. 1982. Emotion in the Human Face, 2nd Edition. Cambridge: Cambridge University Press.
- McNeil, D. 1992. Hand and Mind. What gestures reveal about thought. Chicago and London: University of Chicago Press.
- Kendon, A. 1988. Sign Languages of Aboriginal Australia. Cambridge: Cambridge University Press.
- MacNeilage, Peter, 2008. The Origin of Speech. Oxford: Oxford University Press.
- Lieberman, P.; Crelin, E. S.; Klatt, D. H. (1972). "Phonetic ability and related anatomy of the newborn, adult human, Neanderthal man, and the chimpanzee". American Anthropologist. 74: 287–307. doi:10.1525/aa.1972.74.3.02a00020.
- Stevens, K. N. 1972. The quantal nature of speech: Evidence from articulatory-acoustic data. In P. B. Denes and E. E. David, Jr. (eds.), Human Communication: A unified view. New York: McGraw-Hill, pp. 51–66.
- Ladefoged, P. and Maddieson, I. 1996. The Sounds of the World's Languages. Malden: MA: Blackwell.
- MacLarnon, A. 2012. The anatomical and physiological basis of human speech production: adaptations and exaptations. In M. Tallerman and K. .Gibson (eds.), The Oxford Handbook of Language Evolution. Oxford: Oxford University Press, pp. 224-235.
- MacLarnon, A. M. (1993). The vertebral canal. In A. Walker and R. Leakey (eds.), The Nariokotome Homo erectus skeleton. Cambridge, Massachusetts: Harvard University Press, 359–90.
- MacLarnon AM, Hewitt GP (July 1999). "The evolution of human speech: the role of enhanced breathing control". Am. J. Phys. Anthropol. 109 (3): 341–63. doi:10.1002/(SICI)1096-8644(199907)109:3<341::AID-AJPA5>3.0.CO;2-2. PMID 10407464.
- Maclarnon, Ann; Hewitt, Gwen (2004). "Increased breathing control: Another factor in the evolution of human language". Evolutionary Anthropology: Issues, News, and Reviews. 13 (5): 181–197. doi:10.1002/evan.20032.
- Fitch, WT. (2000). "The phonetic potential of nonhuman vocal tracts: comparative cineradiographic observations of vocalizing animals". Phonetica. 57 (2–4): 205–18. doi:10.1159/000028474. PMID 10992141.
- Fitch, WT.; Reby, D. (Aug 2001). "The descended larynx is not uniquely human". Proc Biol Sci. 268 (1477): 1669–75. doi:10.1098/rspb.2001.1704. PMC . PMID 11506679.
- Weissengruber, GE.; Forstenpointner, G.; Peters, G.; Kübber-Heiss, A.; Fitch, WT. (Sep 2002). "Hyoid apparatus and pharynx in the lion (Panthera leo), jaguar (Panthera onca), tiger (Panthera tigris), cheetah (Acinonyxjubatus) and domestic cat (Felis silvestris f. catus)". J Anat. 201 (3): 195–209. doi:10.1046/j.1469-7580.2002.00088.x. PMC . PMID 12363272.
- Lieberman, Philip (2007). "The Evolution of Human Speech: Its Anatomical and Neural Bases" (PDF). Current Anthropology. 48 (1): 39–66. doi:10.1086/509092.
- Nishimura, T.; Mikami, A.; Suzuki, J.; Matsuzawa, T. (Sep 2006). "Descent of the hyoid in chimpanzees: evolution of face flattening and speech". J Hum Evol. 51 (3): 244–54. doi:10.1016/j.jhevol.2006.03.005. PMID 16730049.
- M. Clegg 2001. The Comparative Anatomy and Evolution of the Human Vocal Tract Unpublished thesis, University of London.
- Perreault, C.; Mathew, S. (2012). "Dating the origin of language using phonemic diversity". PLoS ONE. 7 (4): e35289. doi:10.1371/journal.pone.0035289. PMC . PMID 22558135.
- Jon Hamilton (14 March 2017). "Orangutan's Vocal Feats Hint At Deeper Roots of Human Speech".
- John J. Ohala, 2000. The irrelevance of the lowered larynx in modern Man for the development of speech. Paris, ENST: The Evolution of Language, pp. 171-172.
- Fitch, W. T. (2002). Comparative vocal production and the evolution of speech: Reinterpreting the descent of the larynx. In A. Wray (ed.), The Transition to Language. Oxford: Oxford University Press, pp. 21–45.
- Wynn & Coolidge, p.27
- Wade, Nicholas (19 October 2007). "Neanderthals Had Important Speech Gene, DNA Evidence Shows". The New York Times. Retrieved 18 May 2009.
- Lieberman, Philip; Edmund S. Crelin (Spring 1971). "On the Speech of Neanderthal Man". Linguistic Inquiry. 2 (2): 203–222. JSTOR 4177625.
- Nishimura, T.; Mikami, A.; Suzuki, J.; Matsuzawa, T. (Jun 2003). "Descent of the larynx in chimpanzee infants". Proc Natl Acad Sci U S A. 100 (12): 6930–3. doi:10.1073/pnas.1231107100. PMC . PMID 12775758.
- Boë, L.J.; et al. (2002). "The potential of Neandertal vowel space was as large as that of modern humans". Journal of Phonetics. 30: 465–484. doi:10.1006/jpho.2002.0170.
- Arensburg, B.; Schepartz, LA.; Tillier, AM.; Vandermeersch, B.; Rak, Y. (Oct 1990). "A reappraisal of the anatomical basis for speech in Middle Palaeolithic hominids". Am J Phys Anthropol. 83 (2): 137–146. doi:10.1002/ajpa.1330830202. PMID 2248373.
- Arensburg B, Tillier AM, Vandermeersch B, Duday H, Schepartz LA, Rak Y (April 1989). "A Middle Palaeolithic human hyoid bone". Nature. 338 (6218): 758–60. doi:10.1038/338758a0. PMID 2716823.
- Granat et al., Hyoid bone and larynx in Homo. Estimated position by biometrics, Biom. Hum. et Anthropolol., 2006, 24, 3-4, 243–255.
- Boë, L.J. et al., Variation and prediction of the hyoid bone position for modern Man and Neanderthal, Biom. Hum. et Anthropolol., 2006, 24, 3-4, 257–271
- Martínez I.; Rosa M.; Arsuaga J.L.; Jarabo P.; Quam R.; Lorenzo C.; Gracia A.; Carretero J.M.; Bermúdez de Castro J.M.; Carbonell E. (July 2004). "Auditory capacities in Middle Pleistocene humans from the Sierra de Atapuerca in Spain". Proceedings of the National Academy of Sciences. 101 (27): 9976–81. doi:10.1073/pnas.0403595101. PMC . PMID 15213327.
- Kay, R. F.; Cartmill, M.; Balow, M. (1998). "The hypoglossal canal and the origin of human vocal behavior". Proceedings of the National Academy of Sciences of the USA. 95: 5417–5419. doi:10.1073/pnas.95.9.5417.
- DeGusta, D.; Gilbert, W. H.; Turner, S. P. (1999). "Hypoglossal canal size and hominid speech". Proceedings of the National Academy of Sciences of the USA. 96: 1800–1804. doi:10.1073/pnas.96.4.1800.
- Jungers, W. L.; Pokempner, A. A.; Kay, R. F.; Cartmill, M. (2003). "Hypoglossal canal size in living hominoids and the evolution of human speech". Human Biology. 75: 473–484. doi:10.1353/hub.2003.0057.
- Jakobson, R., Gunnar, C., Fant, M. and Halle, M. 1952. Preliminaries to Speech Analysis. Cambridge, Massachusetts: MIT Press.
- Jakobson, R. and M. Halle 1956. Fundamentals of Language. The Hague: Mouton.
- Jakobson, R. 1938. "Observations sur le classement phonologiques des consonnes", in Proceedings of the 3rd International Congress of Phonetic Sciences, Ghent.
- Chomsky, N. 1957. Syntactic Structures. The Hague: Mouton.
- Chomsky, N. 1964 . The logical basis of linguistic theory. In H.G. Lunt (ed.), The Proceedings of the Ninth International Congress of Linguists. The Hague: Mouton, pp. 914-77.
- Chomsky, N. and Halle, M. 1968. The Sound Pattern of English. New York: Harper and Row.
- Chomsky, N. 1965. Aspects of the Theory of Syntax. Cambridge, Massachusetts: MIT Press, pp. 148-192.
- Ladefoged, P. and Maddieson, I. 1996. The Sounds of the World's Languages. Oxford: Blackwell.
- Ladefoged, P. 2006. Features and Parameters for Different Purposes. http://www.linguistics.ucla.edu/people/ladefoge/PLfeaturesParameters.pdf
- Oudeyer, Pierre-Yves (2006). Self-organization in the evolution of speech. Oxford University Press; New York: Oxford University Press. ISBN 978-0-19-928915-8. OCLC 65203001.
- Lindblom, B., MacNeilage, P. and Studdert-Kennedy, M. 1984. Self-organizing processes and the explanation of language universals. In M. Butterworth, B. Comrie and Ö Dahl (eds), Explanations for language universals. Berlin: Walter de Gruyter and Co., pp. 181-203.
- de Boer, B. 2005b. Self-organisation in language. In C. Hemelrijk (ed.), Self-organisation and evolution of social systems. Cambridge: Cambridge University Press, 123–139.
- Hurford, J. R, J. R. (2000). Chris Knight; Michael Studdert-Kennedy; James R Hurford, eds. Social transmission favours linguistic generalization. The Evolutionary emergence of language : social function and the origins of linguistic form. Cambridge ; New York: Cambridge University Press. pp. 324–352. ISBN 978-0-521-78157-2. OCLC 807262339.
- Steels, L (1995). "A self-organizing spatial vocabulary". Artificial Life. 2: 319–332. doi:10.1162/artl.1995.2.319.
- Steels, L. and Vogt, P. 1997. Grounding adaptive language games in robotic agents. In P. Harvey and P. Husbands (eds.), Proceedings of the 4th European Conference on Artificial Life. Cambridge, Massachusetts: MIT Press, 474–482.
- Berrah A-R., Glotin H., Laboissière R., Bessière P., Boë L-J. 1996. From Form to Formation of Phonetic Structures: An Evolutionary Computing Pers- pective, in Proc. ICML 1996 Workshop on Evolutionary Computing and Machine Learning, pp. 23-29, Bari, Italy.
- de Boer, B (2000). "Self-organization in vowel systems". Journal of Phonetics. 28: 441–465. doi:10.1006/jpho.2000.0125.
- Moulin-Frier C., Laurent R., Bessière P., Schwartz J.-L., and Diard J. 2012 Adverse Conditions Improve Distinguishability of Auditory, Motor and Perceptuo- Motor Theories of Speech Perception: an Exploratory Bayesian Modeling Study. Language and Cognitive Processes, 27(7–8):1240–1263.
- de Boer, B. 2012. Self-organization and language evolution. In M. Tallerman and K. Gibson (eds), 2012. The Oxford Handbook of Language Evolution. Oxford: Oxford University Press, pp. 612-620.
- Lindblom. B. 1986. Phonetic universals in vowel systems. In J. J. Ohala and J. J. Jaeger (eds.), Experimental Phonology. Orlando: Academic Press, pp. 13-14.
- Oudeyer P-Y. 2005. The Self-Organization of Speech Sounds, Journal of Theoretical Biology, 233(3), pp. 435–449.
- Premack, David & Premack, Ann James. The Mind of an Ape, ISBN 0-393-01581-5.
- Kimura, Doreen (1993). Neuromotor Mechanisms in Human Communication. Oxford: Oxford University Press. ISBN 978-0-19-505492-7.
- Newman, A. J.; et al. (2002). "A Critical Period for Right Hemisphere Recruitment in American Sign Language Processing". Nature Neuroscience. 5 (1): 76–80. doi:10.1038/nn775. PMID 11753419.
- McNeill, D. 1992. Hand and mind. Chicago, IL: University of Chicago Press.
- McNeill, D. (ed.) 2000. Language and gesture. Cambridge: Cambridge University Press.
- MacNeilage, P. 1998. Evolution of the mechanism of language output: comparative neurobiology of vocal and manual communication. In J. R. Hurford, M. Studdert Kennedy and C. Knight (eds), Approaches to the Evolution of Language. Cambridge: Cambridge University Press, pp. 222 41.
- Corballis, M. C. 2002. Did language evolve from manual gestures? In A. Wray (ed.), The Transition to Language. Oxford: Oxford University Press, pp. 161-179.
- Johanna Nichols, 1998. The origin and dispersal of languages: Linguistic evidence. In Nina Jablonski and Leslie C. Aiello, eds., The Origin and Diversification of Language, pp. 127-70. (Memoirs of the California Academy of Sciences, 24.) San Francisco: California Academy of Sciences.
- Perreault, C.; Mathew, S. (2012). "Dating the origin of language using phonemic diversity". PLoS ONE. 7 (4): e35289. doi:10.1371/journal.pone.0035289.
- Maddieson, I. 1984. Patterns of Sounds. Cambridge: Cambridge University Press.
- Maddieson, I.; Precoda, K. (1990). "Updating UPSID". UCLA Working Papers in Phonetics. 74: 104–111.
- Keith Hunley, Claire Bowern, and Meghan Healy ("Rejection of a serial founder effects model of genetic and linguistic coevolution", Proceedings of the Royal Society B, 2/1/2012
- Bowern, Claire. 2011 Out of Africa? The logic of phoneme inventories and founder effects. Linguistic Typology. Volume 15, Issue 2, Pages 207–216, ISSN (Online) 1613-415X, ISSN (Print) 1430-0532, DOI: 10.1515/lity.2011.015, November 2011
- Darwin, C. (1871). The Descent of Man, and Selection in Relation to Sex, 2 vols. London: Murray, p. 56.
- Müller, F. M. 1996 . The theoretical stage, and the origin of language. Lecture 9 from Lectures on the Science of Language. Reprinted in R. Harris (ed.), The Origin of Language. Bristol: Thoemmes Press, pp. 7-41.
- Paget, R. 1930. Human speech: some observations, experiments, and conclusions as to the nature, origin, purpose and possible improvement of human speech. London: Routledge & Kegan Paul.
- Firth, J. R. 1964. The Tongues of Men and Speech. London: Oxford University Press, pp. 25-6.
- Stam, J. H. 1976. Inquiries into the origins of language. New York: Harper and Row, p. 243-44.
- Zahavi, A (1993). "The fallacy of conventional signalling". Philosophical Transactions of the Royal Society of London. 340: 227–230. doi:10.1098/rstb.1993.0061.
- Maynard Smith, J (1994). "Must reliable signals always be costly?". Animal Behaviour. 47: 1115–1120. doi:10.1006/anbe.1994.1149.
- Slocombe, K. 2012. Have we underestimated great ape vocal capacities? In M. Tallerman and K. Gibson (eds), The Oxford Handbook of Language Evolution. Oxford: Oxford University Press, pp. 90-95.
- Byrne, R. and A. Whiten (eds) 1988. Machiavellian Intelligence. Social expertise and the evolution of intellect in monkeys, apes, and humans. Oxford: Clarendon Press.
- Knight, Chris (1998). James R Hurford; Michael Studdert-Kennedy; Chris Knight, eds. Ritual/speech coevolution: a solution to the problem of deception (PDF). Approaches to the evolution of language : social and cognitive base. Cambridge, UK ; New York: Cambridge University Press. pp. 68–91. ISBN 978-0-521-63964-4. OCLC 37742390.
- Power, Camilla (1998). James R Hurford; Michael Studdert-Kennedy; Chris Knight, eds. Old wives' tales: the gossip hypothesis and the reliability of cheap signals. Approaches to the evolution of language : social and cognitive base. Cambridge, UK ; New York: Cambridge University Press. pp. 111–129. ISBN 978-0-521-63964-4. OCLC 37742390.
- Fitch, W. T. (2004). Ulrike Griebel; D Kimbrough Oller, eds. Kin selection and "mother tongues" : a neglected component in language evolution. Evolution of communication systems : a comparative approac. Cambridge, Massachusetts: MIT Press. pp. 275–296. ISBN 978-0-262-15111-5. OCLC 845673575.
- Hamilton, WD. (Jul 1964). "The genetical evolution of social behaviour. I.". J Theor Biol. 7 (1): 1–16. doi:10.1016/0022-5193(64)90038-4. PMID 5875341.
- Hamilton, WD. (Jul 1964). "The genetical evolution of social behaviour. II". J Theor Biol. 7 (1): 17–52. doi:10.1016/0022-5193(64)90039-6. PMID 5875340.
- Tallerman, M. In press. Kin selection, pedagogy and linguistic complexity: whence protolanguage. In R. Botha and M. Everaert (eds), The Evolutionary Emergence of Human Language. Oxford: Oxford University Press.
- Ulbæk, Ib (1998). James R Hurford; Michael Studdert-Kennedy; Chris Knight, eds. The origin of language and cognition. Approaches to the evolution of language : social and cognitive base. Cambridge, UK ; New York: Cambridge University Press. pp. 30–43. ISBN 978-0-521-63964-4. OCLC 37742390.
- Trivers, R. L. (1971). "The evolution of reciprocal altruism". Quarterly Review of Biology. 46: 35–57. doi:10.1086/406755.
- Knight, Chris (2006). Angelo Cangelosi; Andrew D M Smith; Kenny Smith, eds. Language co-evolved with the rule of law (PDF). The evolution of language : proceedings of the 6th international conference (EVOLANG6) , Rome, Italy, 12–15 April 200. New Jersey: World Scientific. doi:10.1007/s11299-007-0039-1. ISBN 9789812566560. OCLC 70797781.
- Dessalles, J.-L. 1998. Altruism, status and the origin of relevance. In J. R. Hurford, M. Studdert-Kennedy and C. Knight (eds), Approaches to the Evolution of Language. Social and cognitive bases. Cambridge: Cambridge University Press, pp. 130-147.
- Dunbar, R. I. M. (1996). Grooming, gossip and the evolution of language. London: Faber and Faber. ISBN 9780571173969. OCLC 34546743.
- Donald, M. 1998. Mimesis and the Executive Suite: missing links in language evolution. In J. R. Hurford, M. Studdert Kennedy and C. Knight (eds), Approaches to the Evolution of Language: Social and cognitive bases. Cambridge: Cambridge University Press, pp. 44-67.
- Donald, M. 1999. Preconditions for the evolution of protolanguage. In Corballis, M. and S. E. G. Lea (eds), 1999. The Descent of Mind. Psychological perspectives on hominid evolution. Oxford: Oxford University Press, pp. 138-154.
- Lewis, Jerome (2009). Rudolf P Botha; Chris Knight, eds. As Well as Words: Congo Pygmy Hunting, Mimicry, and Play,. The cradle of language. Oxford ; New York: Oxford University Press. pp. 236–256. ISBN 978-0-19-954586-5. OCLC 804498749.
- Gintis, H.; Smith, E. A.; Bowles, S. (2001). "Cooperation and costly signaling". Journal of Theoretical Biology. 213: 103–119. doi:10.1006/jtbi.2001.2406.
- Rousseau, J.-J. 1973 . The social contract. In Jean-Jacques Rousseau, The Social Contract and Discourses. Trans. G. D. H. Cole. New edition. London & Melbourne: Dent, pp. 179-309.
- Knight, Chris (2000). Chris Knight; Michael Studdert-Kennedy; James R Hurford, eds. Play as precursor of phonology and syntax. The Evolutionary emergence of language : social function and the origins of linguistic form. Cambridge ; New York: Cambridge University Press. pp. 99–119. ISBN 978-0-521-78157-2. OCLC 807262339.
- Knight, C. (2008). ""Honest fakes" and language origins" (PDF). Journal of Consciousness Studies. 15 (10–11): 236–48.
- Rappaport, R. A. 1999. Ritual and Religion in the Making of Humanity. Cambridge: Cambridge University Press.
- Enfield, N. J. (2010). "Without social context?" (PDF). Science. 329: 1600–1601. doi:10.1126/science.1194229.
- Watts, Ian (2009). Rudolf P Botha; Chris Knight, eds. Red Ochre, Body Painting, and Language: Interpreting the Blombos Ochre. The cradle of language. Oxford ; New York: Oxford University Press. pp. 62–92. ISBN 978-0-19-954586-5. OCLC 804498749.
- Steels, L. (2009). Rudolf P. Botha, Chris Knight, eds. Is sociality a crucial prerequisite for the emergence of language?. The prehistory of language. Oxford ; New York: Oxford University Press. ISBN 978-0-19-954587-2. OCLC 819189595.
- Deacon, Terrence William. (1997). The symbolic species : the co-evolution of language and the brain. New York: W.W. Norton. ISBN 978-0-393-03838-5. OCLC 807018262.
- Knight, C. 2010. The origins of symbolic culture. In Ulrich J. Frey, Charlotte Störmer and Kai P. Willfuhr (eds) 2010. Homo Novus — A Human Without Illusions. Berlin, Heidelberg: Springer-Verlag, pp. 193-211.
- Rappaport, R. A. 1979. Ecology, Meaning, and Religion. Berkeley, California: North Atlantic Books.
- Searle, John R. (1995). The construction of social reality. New York: Free Press. ISBN 978-0-02-928045-4. OCLC 31411549.
- Durkheim, E. 1947 . Origins of these beliefs. Chapter VII. In É. Durkheim, The Elementary Forms of the Religious Life. A study in religious sociology. Trans. J. W. Swain. Glencoe, Illinois: The Free Press, pp. 205-39.
- Chris Knight and Jerome Lewis, 2017. Wild Voices: Mimicry, Reversal, Metaphor and the Emergence of language. Current Anthropology Volume 58, Number 4, pp. 435-453.
- Noam Chomsky (2011): Language and Other Cognitive Systems. What Is Special About Language?, Language Learning and Development, 7:4, 263-278
- Chomsky, N (2005). "Three factors in language design". Linguistic Inquiry. 36 (1): 1–22. doi:10.1162/0024389052993655.
- Donovan, J. 1891-92. The festal origin of human speech, part I. Mind 16(64), pp. 495-506.
- Langer, S. 1957 . Philosophy in a New Key. Cambridge, Massachusetts: Harvard University Press.
- Durkheim, E. 1976 . The Elementary Forms of the Religious Life. Translated by Joseph Ward Swain. Introduction by Robert Nisbet. London: Allen & Unwin.
- Brown, S. 2000. The Musilanguage model of music evolution. In N. L. Wallin, B. Merker, and S. Brown (eds.), The origins of music. Cambridge, Massachusetts: MIT Press, 271–300.
- Knight, C. 1999. Sex and language as pretend-play. In R. Dunbar, C. Knight and C. Power (eds), The Evolution of Culture. Edinburgh: Edinburgh University Press, pp. 228-47.
- Mithen, Steven J. (2006). The singing neanderthals: The origins of music, language, mind, and body. Cambridge, Massachusetts: Harvard University Press. ISBN 978-0-674-02192-1. OCLC 62090869.
- Richman, B. 2000. How music fixed "nonsense" into significant formulas: on rhythm, repetition, and meaning. In N. L. Wallin, B. Merker and S. Brown (eds), The Origins of Music: An introduction to evolutionary musicology. Cambridge, Massachusetts: MIT Press, pp. 301-314.
- Wray, A (2000). Chris Knight; Michael Studdert-Kennedy; James R Hurford, eds. Holistic Utterances in Protolanguage: The Link from Primates to Humans. The Evolutionary emergence of language : social function and the origins of linguistic form. Cambridge ; New York: Cambridge University Press. pp. 285–302. ISBN 978-0-521-78157-2. OCLC 807262339.
- Whiten, A. 1999. The evolution of deep social mind in humans. In M. Corballis and S. E. G. Lea (eds), The Descent of Mind. Psychological perspectives on hominid evolution. Oxford: Oxford University Press, pp. 173-193.
- Knight, C. and C. Power (2011). Social conditions for the evolutionary emergence of language. In M. Tallerman and K. Gibson (eds), Handbook of Language Evolution. Oxford: Oxford University Press, pp. 346-49.
- Tomasello, M. 1999. The Cultural Origins of Human Cognition. Cambridge, Massachusetts: Harvard University Press.
- Tomasello, M. 2006, Why don't apes point? In N. J. Enfield & S. C. Levinson (eds), Roots of Human Sociality: Culture, cognition and interaction. Oxford & New York: Berg, pp. 506-524.
- Tomasello, M. 2008. Origins of Human Communication. Cambridge, Massachusetts: MIT Press.
- Erdal, D.; Whiten, A. (1994). "On human egalitarianism: an evolutionary product of Machiavellian status escalation?". Current Anthropology. 35 (2): 175–183. doi:10.1086/204255.
- Erdal, D. and A. Whiten 1996. Egalitarianism and Machiavellian intelligence in human evolution. In P. Mellars and K. Gibson (eds), Modelling the Early Human Mind. Cambridge: McDonald Institute Monographs, pp. 139-150.
- Boehm, C. 1997. Egalitarian behaviour and the evolution of political intelligence. In A. Whiten and R. W. Byrne (eds), Machiavellian Intelligence II: Extensions and evaluations. Cambridge: Cambridge University Press, pp. 341-364.
- Boehm, C. 2001. Hierarchy in the Forest. The evolution of egalitarian behavior. Cambridge, Massachusetts: Harvard University Press.
- Falk, D (2004). "Prelinguistic evolution in early Hominins: Whence motherese?". Behavioral and Brain Sciences. 27: 491–503. doi:10.1017/s0140525x04000111.
- Hrdy, Sarah Blaffer (2009). Mothers and others : the evolutionary origins of mutual understanding. Cambridge, Massachusetts: Belknap Press of Harvard University Press. ISBN 978-0-674-03299-6. OCLC 261174072.
- Hawkes, K.; O'Connell, JF.; Jones, NG.; Alvarez, H.; Charnov, EL. (Feb 1998). "Grandmothering, menopause, and the evolution of human life histories". Proc Natl Acad Sci U S A. 95 (3): 1336–9. doi:10.1073/pnas.95.3.1336. PMC . PMID 9448332.
- Zuberbühler, K. 2012. Cooperative breeding and the evolution of vocal flexibility. In Tallerman, M. and K. Gibson (eds), The Oxford Handbook of Human Evolution. Oxford: Oxford University Press, pp. 71-81.
- Jakobson, R. 1960. "Why 'Mama' and 'Papa'". In B. Caplan and S. Wagner (eds), Essays in Honor of Heinz Werner. New York: International Universities Press, pp. 124-134; p. 130.
- MacNeilage, P. 2008. The Origin of Speech. Oxford: Oxford University Press, pp. 144-154.
- Kenneally, Christine. (2007). The first word : the search for the origins of language. New York: Viking. ISBN 978-0-670-03490-1. OCLC 80460757.
- Richerson, P. J. and R. Boyd, 2004. Not by Genes Alone: How culture transformed human evolution. Chicago: Chicago University Press.
- Laland, K. N.; Odling-Smee, J.; Feldman, M.W. (2001). "Cultural niche construction and human evolution". Journal of Evolutionary Biology. 14: 22–33. doi:10.1046/j.1420-9101.2001.00262.x.
- Odling-Smee, J. and K. N. Laland, 2009. Cultural niche-construction: evolution's cradle of language. In R. Botha and C. Knight (eds.), The Prehistory of Language. Oxford: Oxford University Press, pp. 99-121.
- Pinker, S. (2003) Language as an adaptation to the cognitive niche, in M. H. Christiansen and S. Kirby (eds), Language Evolution. Oxford: Oxford University Press, pp. 16-37.
- Skinner, B. F. 1957. Verbal Behavior. New York: Appleton Century Crofts.
- Chomsky, N (1959). "Review of B. F. Skinner's Verbal Behavior". Language. 35 (1): 26–58.
- Chomsky, N. 1966. Cartesian Linguistics. A chapter in the history of rationalist thought. New York: Harper and Row.
- J. A. Fodor, 1983. The Modularity of Mind: An Essay on Faculty Psychology, Cambridge, Massachusetts: MIT Press.
- Gardner, H. 1985. The Mind's New Science. A history of the cognitive revolution. New York: Basic Books.
- Johnson, D. M. and C. E. Erneling (eds.), 1997. The Future of the Cognitive Revolution. Oxford: Oxford University Press.
- Chomsky, N. 2002. On Nature and Language. Cambridge: Cambridge University Press, pp. 45-60.
- Chomsky, N. 1980. Rules and Representations. New York: Columbia University Press.
- Chomsky, N. 1965. Aspects of the Theory of Syntax. Cambridge, Massachusetts: MIT Press.
- Chomsky, N. 2000. The Architecture of Language. Oxford: Oxford University Press.
- Austin, J. L. 1978 . How to Do Things with Words. Oxford: Oxford University Press.
- Austin, J. L. 1962. How To Do Things With Words. Oxford: Oxford University Press, p.24.
- Searle, J. 1969. Speech Acts. An essay in the Philosophy of Language. Cambridge: Cambridge University Press.
- Tomasello, M. 2006, Why don't apes point? In N J Enfield & S C Levinson (eds), Roots of Human Sociality: Culture, cognition and interaction. Oxford & New York: Berg, pp. 506-524.
- Barbieri, M. 2003. The Organic Codes. An Introduction to Semantic Biology. Cambridge, UK: Cambridge University Press.
- Pattee, H. H. 1980. Clues from molecular symbol systems. In U. Bellugi and M. Studdert-Kennedy (eds), Signed and Spoken Language: Biological Constraints on Linguistic Form. Dahlem Konferenzen, Verlag-Chemie, pp. 261-274.
- Pattee, H. H. (2008). "Physical and functional conditions for symbols, codes and languages". Biosemiotics. 1 (2): 147–168. doi:10.1007/s12304-008-9012-6.
- Sebeok, Thomas A.; Hoffmeyer, Jesper; Emmeche, Claus (eds.) (1999). Biosemiotica. Berlin & New York: Mouton de Gruyter.
- Zahavi, A. (Sep 1975). "Mate selection-a selection for a handicap". J Theor Biol. 53 (1): 205–14. doi:10.1016/0022-5193(75)90111-3. PMID 1195756.
- Zahavi, A. (Aug 1977). "The cost of honesty (further remarks on the handicap principle)". J Theor Biol. 67 (3): 603–5. doi:10.1016/0022-5193(77)90061-3. PMID 904334.
- Zehavi, Amots.; Zahavi, Avishag. (1997). The handicap principle : a missing piece of Darwin's puzzle. New York: Oxford University Press. ISBN 978-0-19-510035-8. OCLC 35360821.
- Maynard Smith, John; Harper, David (2003). Animal signal. New York: Oxford University Press. ISBN 978-0-19-852685-8. OCLC 54460090.
- Chomsky, N. 2000. The Architecture of Language. Oxford: Oxford University Press, pp. 17-18..
- Dessalles, Jean-Louis. (2007). Why we talk : the evolutionary origins of language. Oxford ; New York: Oxford University Press. ISBN 978-0-19-927623-3. OCLC 71329834.
- Trivers, R. L. 1985. Social Evolution. Menlo Park, CA: Benjamin/Cummings.
- Hurford, James R.; Studdert-Kennedy, Michael.; Knight, Chris (1998). Approaches to the evolution of language : social and cognitive base. Cambridge, UK ; New York: Cambridge University Press. ISBN 978-0-521-63964-4. OCLC 37742390.
- Dunbar, Robin I.M.; Knight, Chris; Power, Camilla. (1999). The evolution of culture : an interdisciplinary vie. Edinburgh: Edinburgh University Press. ISBN 978-0-7486-1076-1. OCLC 807340111.
- Knight, Chris; Studdert-Kennedy, Michael.; Hurford, James R. (2000). The Evolutionary emergence of language : social function and the origins of linguistic form. Cambridge ; New York: Cambridge University Press. ISBN 978-0-521-78157-2. OCLC 807262339.
- Bickerton, D. 2009. Adam's Tongue. New York: Hill and Wang.
- Botha, R. and C. Knight (eds) 2009. The Prehistory of Language. Oxford: Oxford University Press.
- Botha, R. and C. Knight (eds) 2009. The Cradle of Language. Oxford: Oxford University Press.
- Burling, R. 2005. The Talking Ape. How language evolved. Oxford: Oxford University Press.
- Christiansen, M. and S. Kirby (eds), 2003. Language Evolution. Oxford: Oxford University Press.
- Corballis, M. C., 2002. From Hand to Mouth: The Origins of Language. Princeton and Oxford: Princeton University Press.
- Deacon, T. W., 1997. The Symbolic Species: The Co-evolution of Language and the Brain. New York: W.W. Norton.
- de Boer. 2001. "The Origins of Vowels Systems", Oxford University Press.
- de Grolier, E. (ed.), 1983. The Origin and Evolution of Language. Paris: Harwood Academic Publishers.
- Deutscher, G. 2005. The Unfolding of Language. The evolution of mankind's greatest invention. London: Random House.
- Dor, D., C. Knight and J. Lewis (eds), 2014. The Social Origins of Language. Oxford: Oxford University Press.
- Dunbar, R. I. M. 1996. Grooming, Gossip and the Evolution of Language. London: Faber and Faber.
- Dunbar, R. I. M.; Knight, Chris; Power, Camilla. (1999). The evolution of culture : an interdisciplinary view. Edinburgh: Edinburgh University Press. ISBN 978-0-7486-1076-1. OCLC 807340111.
- Fitch, W. T. 2010. The Evolution of Language. Cambridge: Cambridge University Press.
- Harnad, S. R., H. D. Steklis and J. Lancaster (eds), 1976. Origins and Evolution of Language and Speech. New York: Annals of the New York Academy of Sciences.
- Hrdy, S. B. 2009. Mothers and others. The evolutionary origins of mutual understanding. London and Cambridge, Massachusetts: Belknap Press of Harvard University Press.
- Hurford, J. R. 2007. The Origins of Meaning. Language in the light of evolution. Oxford: Oxford University Press.
- Hurford, James R.; Studdert-Kennedy, Michael.; Knight, Chris (1998). Approaches to the evolution of language : social and cognitive bases. Cambridge, UK ; New York: Cambridge University Press. ISBN 978-0-521-63964-4. OCLC 37742390.
- Kenneally, C. 2007. The First Word. The search for the origins of language. New York: Viking.
- Lenneberg, E. H. 1967. Biological Foundations of Language. New York: Wiley.
- Leroi-Gourhan, A. 1993. Gesture and Speech. Trans. A. Bostock Berger. Cambridge, Massachusetts: MIT Press.
- Lieberman, Philip. (1991). Uniquely human : the evolution of speech, thought, and selfless behavior. Cambridge, Massachusetts: Harvard University Press. ISBN 978-0-674-92182-5. OCLC 21764294.
- Lieberman, Philip. (2006). Toward an evolutionary biology of language. Cambridge, Massachusetts: Belknap Press of Harvard University Press. ISBN 978-0-674-02184-6. OCLC 62766735.
- Logan, Robert K. 2007. "The Extended Mind: The Emergence of Language, the Human Mind and Culture. Toronto: University of Toronto Press.
- MacNeilage, P. 2008. The Origin of Speech. Oxford: Oxford University Press.
- Maynard Smith, J. and D. Harper 2003. Animal Signals. Oxford: Oxford University Press.
- Oudeyer, P-Y. (2006) "Self-Organization in the Evolution of Speech", Oxford University Press.
- Tallerman, M. and K. Gibson (eds), 2012. The Oxford Handbook of Language Evolution. Oxford: Oxford University Press.
- Tomasello, M. 2008. Origins of Human Communication. Cambridge, Massachusetts: MIT Press.
- Zahavi, A. and A. Zahavi 1997. The Handicap Principle. A missing piece in Darwin's puzzle. New York and Oxford: Oxford University Press.