Auditory Cheesecake or Amino Acids?
Introduction to Evolutionary Psychology
The recent rise of evolutionary psychology aims to explain all facets of human behavior as a product, or by-product, of evolution. Evolutionary psychologists maintain that each and every characteristic observed in humans is a result of natural or sexual selection, including behaviors. However, there are many elements of human behavior that appear to be extremely difficult to explain in an evolutionary context. Evolutionary explanations of homosexuality, rape, and child abuse draw many criticisms, often from other evolutionary psychologists. A more benign, yet still highly debated element of the human mind is the expression of musicality and its potential influence on the development of language. Essentially all human beings across all known cultures can detect and follow rhythm, move appropriately with a beat, and create and appreciate some type of music (Cross 2006). Music effortlessly provokes a wide range of intense emotions ranging from anger and sadness to blissfulness and peace. Songs are often used to efficiently communicate difficult and complicated feelings such as love, grief, fear, and loss. Music can even induce seemingly automatic and intrinsic rhythmic movements commonly known as dance. A mere song lyric can immediately flood our minds with vivid memories of instances in which that song was played, especially those which have significant meanings in our lives. It is all but universally accepted that language is fundamentally innate, but what about musicality? To many researchers, language and musical ability are two sides of the same coin. Those who cannot play an instrument can usually sing at least hum a tune (Schulkin and Raglan 2014). For most researchers, the question is not if the capacity for musicality exists within our DNA, but rather why? What purpose could possessing an intrinsic musical ability possibly serve in our evolutionary history? As there is no feasible way to fossilize the natural history of music or language development, the ideas presented are based on numerous experiments, postulations, and educated assumptions. Because of a considerable lack of physical evidence, there are several schisms that have arisen between sociobiologists, linguists, evolutionary biologists, psychologists, and philosophers. Many declare that musicality is a strictly human attribute, in terms of production, recognition, and enjoyment (Tallerman 2013). Others argue that music is something that was not only shared previously with our closest ancestors but also currently with other animals, specifically birds and marine mammals (Schulkin and Raglan 2014). Some researchers claim the evidence available demonstrates that music is a purely nonessential by-product of language, providing us with pleasure but not supplying humans with much else in the way of crucial, life-saving adaptations (Cross 2001). However, many more assert that musical ability is not only the driving force behind our languages and cultures but also the single most critical element motivating and shaping the modern human mind (Cross 2001). With this, there is also a divide between those who believe music preceded language and those who feel as though language came first, without the slightest bit of influence from music (Tallerman 2013). The major points of these theories are discussed within this paper. By no means is this an exhaustive review of all available literature, viewpoints, or ideas, but instead a more thorough inspection of several well-known and documented theories and hypotheses.
Musicality of the Avian Mind
The debate of whether or not music is something perceived, appreciated, and produced by other animals or if only by humans delves into a larger issue; do non-human animals possess higher levels of cognitive ability? This debate dates back hundreds, if not thousands of years. The first major hypotheses regarding animal cognition were brought about when Greek philosopher Aristotle stated that humans were the only beings to possess rational souls (Andrews 2014). Centuries later, Descartes would lay the groundwork for most of the Western ideas on animal intelligence, which would be accepted without much resistance for hundreds of years. Arriving at the same conclusion as Aristotle, Descartes proclaimed humans to be the only cognitively proficient animals. He proposed that man was the epitome of cognition, leading all creation in intelligent, creative, and independent thought. On the contrary, philosopher David Hume believed very strongly in the rational and conscious thought of nonhuman animals, going so far as to call those who doubted animal intelligence “stupid and ignorant” (Andrews 2014). Recently, it has become more widely accepted in the scientific community that most advanced vertebrates, as well as some highly developed invertebrates, do in fact have some degree of consciousness, intelligence, and cognition, but what about musicality? Do non-human animals possess the ability to perceive and create music? And if so, what can this teach us about musical evolution in humans? Some of the most compelling and fascinating evidence on the perception of music comes from creatures that are more closely related to crocodiles than to humans: birds. The mysteries of the avian mind have only recently begun to be unraveled. New research has shown that not only are most birds capable of producing complex songs; some are even able to follow and maintain a beat, an ability called beat induction. That is, some species of birds, particularly parrots, demonstrate the ability to synchronize their movements along with music on nearly the same level that humans do, and that this ability to follow rhythm comes from within. Until very recently, beat induction was assumed to be a strictly human attribute, and was often called upon to demonstrate a distinction between human and animal dancing (Strycker 2014). However, thanks to one viral video of a dancing Eleonora cockatoo and the chance occurrence of a neuroscientist viewing it, the definition of beat induction as a purely human feature has been forever altered. Researchers initially assumed the parrot was not actually dancing, but instead merely mirroring the movements of its owner, much like what occurs when dogs, cats, and other animals are seen “dancing.” Yet, when brought to the lab and placed in a room without a human to lead, the bird continued to demonstrate the same types of rhythmic movements. Beyond the initial song, researchers observed the parrots’ reaction to several remixes and alternations in the songs speed. When the tempo was increased, the bird danced faster, when the song was slowed down, the birds’ movements followed (Strycker 2014). These findings led to more research being conducted on hundreds of Internet videos of animals “dancing” in an attempt to discover if this bird was one-of-a-kind or if beat induction was more persistent in the animal kingdom than previously thought. The research showed that out of the hundreds upon hundreds of animal videos sampled, ranging from ferrets to dolphins and everything in between, only thirty-three videos possessed animals that were considered to be truly dancing to the rhythm. The researchers concluded that these videos, including twenty-nine recordings of parrots encompassing fourteen different species and four videos of Asian elephants, were the only ones currently available in which the animals were observed exhibiting true beat induction (Strycker 2014). These findings further our understandings of animal cognition and shake the foundations of the firmly held beliefs of some that music is innately human and that beat induction can only be observed in human beings. Nevertheless, as innovative as these findings are into the musical perception of birds, they do not tell us much about the evolution of musicality in our own lineage, only that we are not alone in recognizing and dancing to a good beat when we hear one. The similarities between human and avian song and dance are those of analogy, not homology. Even so, the exciting possibilities, novel experiments, and revolutionary conclusions that can be made from these new discoveries have yet to be fully explored.
Congo African Grey
Interestingly, more closely related relatives of ours like marine mammals, specifically dolphins and whales, are renowned for their vocal abilities as well as their highly complex songs which they use as their primary means of communication (Fitch 2006b). Can these whale songs provide us with new insights into the development of human musicality and language? Current research suggests that the only mammals, other than humans, able to imitate novel vocal sounds are marine mammals (Mercado and others 2004). Unlike the songs produced by songbirds, which are often bounded by genotypic limitations and strongly influenced by sensorimotor experiences early in development, whale songs change continuously throughout their entire lives. In addition to various species of whales, bottlenose dolphins have been observed spontaneously imitating new sounds in their environment, without any encouragement or outside influence to do so (Mercado and others 2004). While research about this spectacular phenomenon is scarce, as it is extremely difficult to accurately study whale communication in their natural habitat, it is generally accepted that, unlike many types of birds, humpback whales do not converge on a species-specific song, but instead develop their own unique tune based on personal experience (Mercado and others 2004). This song varies greatly across the span of their lives and tends to change according to several different factors including the depth at which the songs are sung, the distance between whales, and the specific spectral content. Despite the highly dynamic nature of the whale songs, particular phases seem to reoccur in certain populations across many decades (Mercado and others 2004). This suggests that there is possibly a genetic component to the distinct song sung by a whale, although it appears that the majority of the influence comes from its environment and experiences. When it comes to vocal production, dolphins and whales have a distinct difference worth noting. Only male whales have been observed producing songs while both sexes of dolphin have been shown to produce song-like vocalizations (Fitch 2006b). This is a reflection of their differing mating styles and social structures. Although it may seem like a stretch to attempt to relate whale song to human song, continuing research in this area is undoubtedly a highly important step in understanding the link between musicality, intelligence, and culture. Whales live long lives in which they develop and maintain numerous social bonds that make some type of communication essential. While some may see this research as a frivolous waste of time, some researchers postulate that controlled laboratory and field studies of animal auditory perception are a critical part of understanding and explaining music perception and production for both animals and humans (Fitch 2006a).
The Case for a Musical Protolanguage
From distantly related animals to our immediate ancestors, it is believed by some that music was the first step in creating a true verbal language. Prior to the spoken-word language, which can be observed in some form by essentially all cultures today, many researchers believe there was a musical protolanguage that was much more melodic than modern human speech (Fitch 2006b). This is an almost ubiquitous theme among papers that postulate that musicality is critical to the development of human language and this non-verbal, song-like protolanguage most likely came first. Many authors point to human infants and the rhythmic quality of modern speech as their primary sources of evidence. Within the first month of birth, human infants are able to discriminate between vowel and phonetic sounds (Boero 2014). It is believed that we as a species are primed for language; but in order for linguistic ability to fully develop, infants must constantly be bombarded with language and human interaction (Cross 2001). Human infants babble and attempt to communicate with those around them within the first few months of life, seemingly before any substantial learning could occur (Cross 2001). Many studies have shown that by six months of age, infants are sensitive to melodic contoural constancy, that is, being able to recognize that two melodies share the same ups and downs despite the fact that the pitch of each of them is different (Cross 2001). It is apparent through these infant studies that culture and human interaction quickly shape these understandings. Very early in life, infants’ hearing is open to all linguistic and musical sounds but this ability is lost at approximately five to six months of age, when infants begin to become attached to their native language, sometimes referred to as the “motherese” (Boero 2014). Moreover, brain scans have demonstrated that newborn babies can form expectations of musical pitch and can additionally detect and distinguish substitution of musical notes (Boero 2014). Experiments have also shown that infants prefer human speech to just about any other sound played for them and this preference begins almost immediately upon birth (Fitch 2006b). Along with the predisposition for language in infants, some researchers point to the song-like structure of human speech as an indication of musicality in our ancestors. Both music and language contain elements such as melody, tone, pitch, and phrasing. Even slightly altering these elements can have drastic implications on their perceived meaning. In some languages, such as Chinese, a mere change in the tone can differentiate between different definitions of an otherwise identical word (Strycker 2014). Another aspect of human vocalization and communication that can potentially demonstrate the phylogeny of human speech is laughter. It is believed that the first laughter-like noises were present prior to the last common ancestor and potentially arose due to alternations in breathing patterns during play activity (Bryant 2014). Today, laughter seems to play a critical role in conversational timing and flow. Amazingly, there even appears to be a difference in the way we perceive spontaneous and volition laughter. Researchers found when spontaneous laughs were played at a slowed speed for individuals; the sounds were practically indistinguishable from animal calls. On the other hand, volitional laughter, even when played slowly, was almost always distinguished as a noise produced by a human being (Bryant 2014). Even before modern research, Darwin believed that the protolanguage was one of non-lyrical songs and that this ability to communicate, along with corresponding rhythmic musical movements, was selected for by sexual selection (Tallerman 2013). Darwin was one of the first proponents of the idea that music predated language and he claimed this became apparent by studying modern words, grammar, and syntax (Strycker 2014). Today, many supporters of the non-lyrical yet musical protolanguage continue to believe that musicality was one of the major elements that distinguished humans from other primitive primate lineages. Some even go as far as to claim that it was one of the most distinctive features between humans and Neanderthals, that is, humans produced less musical noises while Neanderthals communicated strictly through songs (Smith 2006). However, as intriguing as these hypotheses are, without concrete evidence, they remain highly controversial.
Sounds Simply for Pleasure?
In contrast to the idea that musicality was a central component to developing human language, there are those who claim that music and song production came second in the evolution of verbal communication and that spoken word-like sounds were used before music became common. Those who hold this viewpoint often also maintain that music and song production in humans is merely a by-product of our verbal communication and that it serves no real purpose or fundamental importance in human evolution or behavior (Cross 2001). As linguist and evolutionary psychologist Steven Pinker once put it, for humans, music is nothing more than “auditory cheesecake” (Strycker 2014). Many people who support this theory also postulate that music and language likely evolved separately from each other (Tallerman 2013). Proponents of this idea assert that there is a distinct difference between animal and human song; the former has a particular, evolutionally driven function while the latter may or may not. These researchers argue it is obvious that bird song is a sexually selected characteristic and therefore essential for survival. Birds frequently display complex behaviors that enhance their chances of reproducing, which indicates the intrinsic value of the trait. On the other hand, human music is created rather than displayed and if it is related to fitness, it is not immediately apparent in what way (Tallerman 2013). In addition, they point out that in the animal kingdom males are the ones that primarily perform, display, and vocalize songs while in humans, both males and females exhibit musical ability. This calls them to question the sexual selection theory of language development and suggest that the protolanguage had a purely semantic form, where single noises were designated to have a particular, distinct meaning (Tallerman 2013). Those who doubt the musical origin of language claim that music merely exploits certain human capabilities, several of which they believe do in fact have adaptive purposes (Cross 2001). However, they argue that producing music was not the primary function of these traits and thus musicality is not necessary for human survival or evolution. One of these adaptations is the effortless detection of changes in patterns of pitch. Researchers point out that in our hominin ancestors, the ability to detect changing pitch would have been critical to understanding and interpreting incoming calls and warnings. Those who lacked the ability to comprehend the important messages others were conveying vocally would have quickly died out, making the genes that coded for pitch detection more prominent in the population (Cross 2006). Nevertheless, to those who question the importance of music in our development, the musical side effect of these genes is purely coincidental and to this very day, holds not a shred of importance in our survival as a species. For those who question the intrinsic musicality of humans, the dozens of infant studies indicate something far different than an innate musical ability. Researchers who doubt the importance of music in our evolutionary history claim that the noises made by infants are products of distinct neural circuits and these sounds have evolved merely to attract their mothers attention, thus increasing their chances of survival. They declare these seemingly instinctive vocalizations may show that humans have an inherent predisposition for language, but not for music (Tallerman 2013). Once again, they argue that music is nothing more than a hedonistic accident and perhaps researchers who believe otherwise are choosing to interpret the evidence in such a way that confirms their ideas.
Many articles written on the evolution of musicality in humans and their ancestors point out that interpreting, producing, and appreciating music requires highly advanced cognitive capabilities. While our brains do in fact process music and language in an almost identical way, our individual understanding of each is extremely different (Strycker 2014). Music does not necessarily have a direct meaning that is unanimously understood in the same way by all who hear it, unlike words, which usually have a distinct denotation relating to a particular utterance. For example, two people may listen to the same song but each one interprets the meaning of what they heard in a drastically different manner. This does not mean that one of them is right and the other one is wrong, but instead that music can create many different ideas in those who take part in it. In this way, music is fundamentally polysemic (Cross 2006). It is believed that this is one of the major reasons music was so crucial to hominin development; it promoted human connection, meaning, and imagination in our ancestors (Schulkin and Raglan 2014). This idea has lead to a relatively new field of study called biomusicology, which is the study of music from a biological point of view. Ian Cross, a major proponent of biomusicology, points that out many of our ancestors, including other species of hominins, had highly developed skills in particular domains of life while Homo sapiens appear to have the ability to transfer their expertise between domains (Cross 2001). This is presented as a primary reason why musical ability was vital to our early ancestors. It permitted them to think abstractly and to develop a significant amount of cognitive flexibility. In addition, it allowed for the capacity to easily express complex emotions as well as providing a more peaceful way of dealing with conflicts and complicated issues, such as mate selection and establishing social order and bonds (Schulkin and Raglan 2014). Support for this idea comes from one of the only concrete pieces of evidence for hominin musicality: the first known musical instrument. While there have been other more ancient, potentially musical artifacts found, the earliest undisputed musical items are 36,000 year old bone flutes found in Geissenklosterle, Germany (Fitch 2006a). This time period is around the same point in history as the cultural explosion as well as the time it is believed that our distant human ancestors and Neanderthals could have been interbreeding (Cross 2001). Those who believe in the strictly song-like communication of Neanderthals are very interested in exploring this idea of potential interbreeding and the effects it may have had on communication and language. For many researchers, the most frustrating part about this is that it is very possible musicality was around for thousands of years before these bone flutes were created, however, hollow tree drums and singing voices are not well preserved. This makes finding evidence of musicality in our more ancient ancestors all but impossible.
Music as the Basis of Modern Human Intelligence
In addition to the importance of developing advanced cognitive functions, some theorists argue that music is absolutely essential to human development, sociality, and behavior. These researchers emphasize that musical ability is the driving force behind the modern human mind and without it, we would have evolved in a way that is much more similar to our chimpanzee and bonobo relatives (Cross 2001). Proponents of this theory combine evidence provided by comparative animal studies and human infant studies. These researchers support the idea of a musical protolanguage and assert that if music was no more than a useless by-product, as Pinker and Tallerman claim, it should be a target for natural selection, eventually causing it to disappear completely (Fitch 2006a). It has been suggested that coordinated vocal behavior allows individuals to accurately assess the fitness of others as cooperative partners. This is believed to have been a major step in the evolution of humans, as we possess an extremely cooperative nature, which is assumed to be one of the reasons we surpassed our primate relatives (Bryant 2014). Researchers have also proposed that music is strongly linked to our motivation, social contacts, and cognitive capabilities. It has been suggested that music is innately part of our biological make-up, that it is critical to human social capability because it interacts with cultural boundaries and allows us to efficiently share our experiences, emotions, and intentions with those around us (Schulkin and Raglan 2014). Much evidence provided for this theory comes from understanding the auditory perception and vocal production of human infants. Infants are far superior to adult humans in their ability to identify absolute pitch, sometimes called “perfect pitch” (Smith 2006). This leads evolutionary psychologists and biomusicologists to point out that at such as young age, it is highly unlikely that learning has much, if any, influence on this behavior; which appears to demonstrate the innate nature of musicality. Proto-musical behaviors observed by infants when interacting with their caregivers include using rhythm and pitch in a musical way. Not only do infants listen to sounds, they are quickly able to produce and even move in unison with them (Cross 2001). Recently it has been shown that human infants as young as two days old are able to recognize a beat within a series of drum rhythms (Strycker 2014). W. Tecumseh Fitch, prominent promoter of the influence of musicality on the development of human language, declares that the question of if music is an adaptation has been far overstated in recent years. In order to further our knowledge on the biological element of musicality and language, he calls for researchers to perform more concrete experiments on living animals and humans rather than continuing to make assumptions and quarrel about various hypotheses regarding our ancestors. Alas, petty arguments between researchers are not furthering our understandings and it is nearly impossible to ever truly know how they communicated and if spoken language was in fact preceded by a more musical one. Fitch advises that human musical ability would be better treated as an “instinct to learn” while also combining cultural and biological elements (Fitch 2006a). From this, we may begin to understand how large of an impact music really has on the human race as a whole.
What is Do You Think?
Why do you believe musicality evolved in humans?
In My Humble Opinion
After reviewing all of the literature presented at great length, it is in my opinion that the most compelling arguments come from the biomusicologists, particularly those who declare that not only is music an integral element to the development of human language and culture, without music, Homo sapiens would have likely evolved in a way much more similar to our closest primate relatives. Without artistic expression and musical ability, the vast majority of human innovation would be drastically reduced or perhaps even absent. It is because of our ability to think so abstractly that essentially all of the major developments and advancements of mankind have come about. In order to be truly innovative, artists, musicians, and scientists must be immensely creative. Perhaps the first step in developing this imaginative skill was imitating sounds heard in nature, altering them slightly, and then recombining them in novel ways to indicate new meanings. It appears to be very logical that performing musical displays, singing, and dancing were initially sexually selected traits, as even today it seems as though 95% of popular music is written about love, sex, an attractive potential mate, or some combination of the three. The example of prospective musical ability in animals, both the auditory perception and production of marine mammals and birds, only furthers strengthens my position. While some parrots may in fact display beat induction, it is a trait that has not yet been observed in the wild, but instead only in captive birds that spend their lives with humans (Strycker 2014). Perhaps we are driving animal evolution by sharing our homes with these highly intelligent animals, which is in turn altering their natural behaviors to more closely match ours. In this, we are finding new ways to more readily relate and connect with these fascinating creatures, many of which have lifespans exceeding sixty-years. Furthermore, denying the extremely tight-knit connection music has to our emotions would be ignoring a critical part of being alive, essentially overlooking an integral piece of what it means to be human. Music is by far one of the most intriguing elements of human cognition, so to write it off as being nothing more than an unimportant accident that just happened to stick with us is not a good enough explanation.
Snowball Can Really Dance!
From dancing parrots and singing whales to babbling infants and melodic ancestors, the debate on the evolution of musicality in humans is only just beginning. Without much concrete evidence from the previous 60,000 years, researchers are often only able to speculate and make educated guesses about the history of language and music production. Studies on cultural effects of music, language, and social structure make strong cases for some theories; however, they can often just as easily be rebutted with other studies or even just a different perspective on the same findings. Research into infant vocal perception and animal song also produce compelling evidence for many of these ideas, yet they often further divide those who believe music is merely a by-product of other adaptations and those who postulate that music is the single most important feature of human language and the modern mind. It is highly unlikely that we will ever know with certainty which came first, how our ancestors communicated, or if musical ability was the element that drove hominin evolution to the extremes of cognitive ability we see today. However, the developments and novel understandings brought about by these overarching questions of human language and musical development advance our body of knowledge and provide fascinating insights into the complicated nature of the human mind, brain, and the relationship between them. Despite all of the turmoil and arguments between the various sides, one thing is certain: music lives within all of us. Song is nearly as important to human beings as social interaction and comes to us just as naturally. Music is a highly effective method of communicating with those around us. Without music, there is a possibility that instead of living in highly advanced cities, we would still be living on the open planes or in caves, much like our ancestors were, void of higher levels of thought, cooperation, and possibly even complex emotions. Music may not be strictly human, but for those of us who embrace it, music makes being human truly remarkable.
Andrews K. Animal Cognition [Internet]: The Stanford Encyclopedia of Philosophy; c2014 [cited 2015 2/21]. Available from: http://plato.stanford.edu/entries/cognition-animal/.
Boero D. Early human communication helps in understanding language evolution. Behavioral and Brain Sciences [Internet]. [revised 12/14;cited 2/21/15]Cambridge Journals. Available from http://journals.cambridge.org.prox.lib.ncsu.edu/action/displayFulltext?type=6&fid=9475057&jid=BBS&volumeId=37&issueId=06&aid=9475056&fulltextType=AC&fileId=S0140525X13004081.
Bryant G. The evolution of coordinated vocalizations before language. Behavioral and Brain Sciences [Internet]. [revised 12/14;cited 2/21/15]Cambridge Journals. Available from http://journals.cambridge.org.prox.lib.ncsu.edu/action/displayFulltext?type=6&fid=9474982&jid=BBS&volumeId=37&issueId=06&aid=9474981&fulltextType=AC&fileId=S0140525X1300397X.
Cross I. Music, mind and evolution. Psychology of Music [Internet]. [revised 2001;cited 2/21/15]ProQuest. Available from http://search.proquest.com.prox.lib.ncsu.edu/docview/1339623?accountid=12725.
Cross I. Music, cognition, culture, and evolution. Annals of the New York Academy of Sciences [Internet]. [revised 6/25/06;cited 2/21/15]Annals of the New York Academy of Sciences. Available from http://onlinelibrary.wiley.com.prox.lib.ncsu.edu/doi/10.1111/j.1749-6632.2001.tb05723.x/full.
Fitch W. On the biology and evolution of music. Music Perception: An Interdisciplinary Journal [Internet]. [revised 9/06(a);cited 2/21/15]University of California Press. Available from http://www.jstor.org.prox.lib.ncsu.edu/stable/10.1525/mp.2006.24.1.85.
Fitch W. The evolution of music in comparative perspective. Annals of the New York Academy of Sciences [Internet]. [revised 4/18/06(b);cited 2/21/15]Annals of the New York Academy of Sciences. Available from http://onlinelibrary.wiley.com.prox.lib.ncsu.edu/doi/10.1196/annals.1360.004/full.
Mercado E, Herman L, Pack A. Song copying by humpback whales: Themes and variations. Animal Cognition [Internet]. [revised 10/15/04;cited 2/21/15]Springer Link. Available from http://link.springer.com.prox.lib.ncsu.edu/article/10.1007/s10071-004-0238-7/fulltext.html.
Schulkin J and Raglan G. The evolution of music and human social capability. Frontiers in Neuroscience [Internet]. [revised 9/17/14;cited 2/21/15]Frontiers in Neuroscience. Available from http://www.ncbi.nlm.nih.gov.prox.lib.ncsu.edu/pmc/articles/PMC4166316/.
Smith N. The evolution of music and language. Current Anthropology [Internet]. [revised 2006;cited 2/21/15]Chicago Journals. Available from http://www.jstor.org.prox.lib.ncsu.edu/stable/10.1086/527676.
Strycker N. 2014. Beat generation. In: The Thing with Feathers. 1st ed. New York, NY: Penguin Group. 129 p.
Tallerman M. Join the dots: A musical interlude in the evolution of language? / The evolution of language. Journal of Linguistics [Internet]. [revised 2/13;cited 2/21/15]Journal of Linguistics. Available from http://journals.cambridge.org.prox.lib.ncsu.edu/action/displayFulltext?type=6&fid=8921678&jid=LIN&volumeId=49&issueId=02&aid=8921677&fulltextType=RV&fileId=S0022226713000017#sec4.