Language evolution: syntax before phonology?

Katie Collier 2 Balthasar Bickel 1 Carel P. van Schaik 0 Marta B. Manser 2 Simon W. Townsend 2 0 Anthropological Institute and Museum, University of Zurich , Zurich , Switzerland 1 Department of Comparative Linguistics 2 Institute of Evolutionary Biology and Environmental Studies Phonology and syntax represent two layers of sound combination central to language's expressive power. Comparative animal studies represent one approach to understand the origins of these combinatorial layers. Traditionally, phonology, where meaningless sounds form words, has been considered a simpler combination than syntax, and thus should be more common in animals. A linguistically informed review of animal call sequences demonstrates that phonology in animal vocal systems is rare, whereas syntax is more widespread. In the light of this and the absence of phonology in some languages, we hypothesize that syntax, present in all languages, evolved before phonology. 1. Introduction Human language and its origins have intrigued philosophers and scientists since early antiquity [1]. This is unsurprising, as language is responsible for much that distinguishes humans from other species and makes us so successful, including the transmission of knowledge [2 5]. Unfortunately, the search for the origins of language is complicated by the fact that language, unlike other biological traits, does not fossilize or leave any traces to study its cumulative evolution. Empirical studies must therefore circumvent this problem and various different approaches have been undertaken to attempt to unpack the evolution of language [6 8]. These include, among others, the study of child language acquisition [9], hominid morphology [10 12], genetics [13] and the use of computer simulations to test specific hypotheses [14 16]. One method that has received particular attention is the exploration of similarities and differences between human language and animal communication systems [6,17]. If similarities are found between humans and a closely related species, then it is possible that they are derived from the same feature present in their common ancestor, representing homologues [18]. If, on the other hand, similarities are found between humans and more distantly related species, these features represent analogues and hence do not give any information on the phylogenetic origins of the feature, but can help elucidate the environmental or social conditions favourable to its convergent evolution [4]. One particular feature of human language that has received considerable attention by both linguists and animal communication researchers, and been highlighted as a fundamental universal structural characteristic [19], is duality of patterning [20,21]. Also known as double articulation [22], duality of patterning is a property of language that allows a combinatorial structure on two levels: (i) phonology, where meaningless sounds called phonemes (i.e. the smallest meaning-differentiating elements of a language that do not themselves have meaning) can be combined into morphemes (i.e. the smallest meaningful elements) and words; and (ii) syntax, in which these morphemes and words can be combined into larger structures [23]. Critically, duality of patterning is the property that allows human languages to create a large lexicon from a few distinct signals [21,24 26]. Unpacking the evolutionary route that led to duality of patterning is thus considered central to a more holistic understanding of language evolution. the way meaningful parts (morphemes, words) go together to form sentences a sequence of meaningful elements whose meaning is a function of the meaning of the individual elements that compose it and the way they are structured together an expression whose meaning is not predictable from the parts that compose it the physical properties of sounds ( phones) meaningless sounds are combined into sequences, the sequences obtained having no conventional meaning minimal meaning-differentiating units ( phonemes) that do not themselves bear meaning recombine to create meaningful expressions meaningful elements combine into a meaningful sequence whose meaning is not a function of the meaning of the parts. visual representation Researchers of vocal communication in animals have emphasized the fact that animals are also capable of forming different types of sound combinations that could potentially be analogous or homologous to one or both levels of duality of patterning found in human languages [2731]. Peter Marler played an important role in establishing the link between the levels of patterning found in human language and the different types of call combinations found in animal communication by introducing the terms phonological and lexical syntax, loosely based on the two levels of duality of patterning [32]. Marler defined phonological syntax (or phonocoding) as the level at which meaningless sounds are combined into sequences, and lexical syntax (or lexicoding) as the higher level at which the meaningful elements are combined. More recently, Hurford has used the terms combinatorial syntax (or combinatoriality) and compositional syntax (or compositionality) to designate the same phenomena as phonological and lexical syntax, respectively [26] (see table 1 for the terms and definitions of sound combinations used in animal communication research and their linguistic equivalents). Our goal here is to examine several examples of animal call combinations from a linguistic perspective and determine which level of duality of patterning they most resemble. 2. Examples of combinations in animal communication systems (a) Winter wrens: phonological syntax? Some of the best-studied examples of animal sound combinations come from birdsong [33]. One classic example of phonological syntax noted by Marler is the song of the winter wren (Troglodytes troglodytes) [32]. Kroodsma & Momose [34] describe the songs of a Japanese population of winter wrens whose song types consist of a highly predictable sequence of notes or syllable types (a note being a continuous trace on a sonogram and a syllable being a repeated unit of identical notes or groups of notes). In their study population, the typical repertoire for a male includes six or seven song types. These different song types are obtained by reusing many of the same syllables or syllable sequences in a different order. However, as Marler noted, these syllables do not differentiate the song types from one another. In fact, all six or seven song types in a male wrens repertoire convey the same message and none of them have any referential meaning [32]. Therefore, while superficially there seem to be structural similarities between bird song and human phonology, there are important differences when it comes to meaning differentiation. For the wrens song to have phonology in the linguistic sense, the different order of syllables in the different song types would have to bring about a c (...truncated)