Beyond the Vocal Learning Dichotomy

Sound production learning across species: Beyond the vocal learning dichotomy Pedro Tiago da Silva Gonçalves Martins Aquesta tesi doctoral està subjecta a la llicència Reconeixement- NoComercial – SenseObraDerivada 4.0. Espanya de Creative Commons. Esta tesis doctoral está sujeta a la licencia Reconocimiento - NoComercial – SinObraDerivada 4.0. España de Creative Commons. This doctoral thesis is licensed under the Creative Commons Attribution-NonCommercial- NoDerivs 4.0. Spain License. Sound production learning across species: Beyond the vocal learning dichotomy Pedro Tiago da Silva Gonc¸alves Martins esis submied to the University of Barcelona in partial fulllment of the requirements of the degree of Doctor of Philosophy in Cognitive Science and Language under the supervision of Dr. Cedric Boeckx ICREA/University of Barcelona Dr. Bridget D. Samuels University of Southern California September 2020 ii Abstract All humans have language. is capacity is a complex biological trait whose evolution is currently an active research topic, especially in recent years. is thesis is an aempt at contributing to this enterprise in two ways, from dierent angles. e rst one is a critical assessment of a prominent theory of language evolution, whereby the “core properties of language” can be reduced to a single computational operation, for- mally irreducible, which evolved suddenly as a result of a single genetic mutation. e second one is an exploration of vocal learning, a trait present in many species which in the case of humans is part of the language capacity as the functional provider of speech. Chapter2 identies a fallacious line of argument associated with the aforemen- tioned theory of language evolution, i.e. that from the formal simplicity of an operation — in the case of this particular hypothesis, the Merge operation — one can derive the evolutionary steps it took for it to emerge. is argument is named here the “no nalf-Merge” fallacy. Aer a summary of independent reasons to doubt this hypothesis for how language evolved, it is shown why the argument is biologically untenable in the rst place. is chapter lends support to the idea that language evolved gradually. e greater part of this thesis (chapters3 and4) focuses on vocal learning. Vo- cal learning, the capacity to modify auditory output on the basis of experience, is displayed by several species, across dierent families. In humans, it is crucial for speech. is thesis looks at vocal learning in two ways, by rst oering an extension to the Vocal Learning Continuum, an inuential framework, and secondly by using genomic information in the human lineage to suggest that vocal learning could have been present in at least some of our ancestors, narrowing the gap between them and modern humans regarding language components. e Vocal Learning Continuum helped move past the dichotomic view according to which species are either vocal learners or non vocal learners, proposing instead a typology with a more nuanced, gradual distribution of this phenotype. However, several issues remain, namely the reliance on a particular brain connection for estab- lishing a vocal learning circuit (forebrain control of phonatory muscles), as well as the primacy given to imitation, which is but one example of vocal learning and not iii iv the whole behavioral spectrum of this phenotype. In chapter3. aer identifying and assessing these limitations, by pointing out conceptual and empirical problems, an extension to the framework is oered, called the Vocal Learning Contiguum, which eschews reliance on particular brain circuits and behaviors, favoring a broader per- spective and welcoming more factors as sources of variation across species. Chapter4 explores a link between the SRGAP2 gene and the emergence of vocal learning in the Homo lineage. SRGAP2C, a duplication of this gene found in Nean- derthals and Denisovans and also in Modern Humans (but no other extant mammals), inhibits SRGAP2A, the ancestral version of the gene, which modulates axon guidance associated with the SLIT-ROBO molecular pathway. A connection is drawn between the downregulatory eect on axon guidance and the formation of a cortico-laryngeal connection associated with the human vocal learning circuit. e thesis is complemented by a series of appendices that delve in more detail into some conceptual issues surrounding the eld of language evolution, namely those coming from linguistics. Resum Tots els humans tenen llenguatge. Aquesta capacitat es´ un tret biologic` complex, l’evolucio´ del qual es´ actualment un tema de recerca molt actiu, especialment en els darrers anys. Aquesta tesi es´ un intent de contribuir en aquesta l´ınia de recerca de dues maneres. La primera es´ una apreciacio´ cr´ıtica d’una teoria prominent d’evolucio´ del llenguatge, segons la qual les “propietats nuclears del llenguatge” es poden reduir a una sola operacio´ computacional, formalment irreductible, la qual va evolucionar de sobte com a resultat d’una sola mutacio´ genetica.` La segona es´ una exploracio´ del aprenentatge vocal, un tret que forma part de la capacitat del llenguatge com a prove¨ıdor funcional de la parla. El cap´ıtol2 identica una l ´ınia argumental fal·losa associada amb la teoria sus- dita d’evolucio´ del llenguatge, i.e. que des de la simplicitat formal d’una operacio´ — en el cas d’aquesta hipotesi,` la operacio´ Fusio´ — es poden derivar els passos evolu- tius necesaris per al seu sorgiment. Aquest argument s’anomena en aquest cap´ıtol “no nalf-Merge fallacy”. Despres´ d’exposar raons independents per dubtar d’aquesta hipotesi` de la evolucio´ del llenguatge, es mostra per que` l’argument es´ biologicament` insostenible. Aquest cap´ıtol dona suport a la idea de que el llenguatge va evolucionar gradualment. La part preponderant d’aquesta tesi (cap´ıtols3i4) es centra en l’aprenentatge vocal: la capacitat de modicar l’output auditiu en base a l’experiencia.` L’aprenentatge vocal esta` present en diverses especies,` de diferents fam´ılies taxonomiques.` En humans, es´ crucial per a la capacitat de la parla. Aquesta tesi analitza aquest tema de dues maneres. En primer lloc s’ofereix una extensio´ d’un marc inuent, el Cont´ınuum de l’Aprenentatge Vocal. En segon lloc s’utilitza informacio´ genomica` del llinatge huma` per suggerir que l’aprenentatge vocal podria haver estat present en com a m´ınim al- guns dels nostres ancestres, reduint el buit entre aquests i els humans moderns pel que fa a components del llenguatge. El Cont´ınuum de l’Aprenentatge Vocal va ajudar a superar la visio´ dicotomica` segons la qual les especies` son´ “aprenedors vocals” o no ho son,´ proposant en el seu lloc una tipologia amb una distribucio´ mes´ matisada i gradual d’aquest fenotip. Tanma- v vi teix, queden certs aspectes per resoldre. Un d’ells es´ la dependencia` en una connexio´ cerebral particular per establir un circuit de aprenentatge vocal (control prosencefalic` dels musculs´ fonatoris). Un altre es´ la primacia donada a l’imitacio,´ la qual, tot i ser un exemple de aprenentatge vocal, no representa la totatilat de l’espectre compor- tamenmtal d’aquest fenotip. En el cap´ıtol3, despr es´ d’identicar i valorar aquestes limitacions, assenyalant problemes conceptuals i emp´ırics, s’ofereix una extensio´ a aquest marc. Aquesta extensio´ rep aqu´ı el nom de Cont´ıguum de l’Aprenentatge Vocal. Aquest abordatge evita la centralitat d’un circuit cerebral o comportament particu- lars, afavorint una perspectiva mes´ ampla i donant la benvinguda a mes´ factors com a fonts de variacio´ entre especies.` El cap´ıtol4 explora un nexe entre el gen SRGAP2 i el sorgiment de l’aprenentatge vocal en el llinatge Homo. SRGAP2C, una duplicacio´ d’aquest gen, present tant en neandertals i denissovans com en humans moderns (pero` no en altres mam´ıfers existents), inhibeix la versio´ ancestral del gen (SRGAP2A), la qual modula el guiatge axonal associat amb la ruta molecular SLIT-ROBO. Com a resultat d’aquesta exploracio,´ es proposa una associacio´ entre l’efecte de regulacio´ negativa en el guiatge axonal i la formacio´ d’una connexio´ cortico-lar´ıngia vinculada al circuit huma` d’aprenentatge vocal. La tesi es complementa amb una serie` d’apendixs` que s’enfoquen amb mes´ detall en algunes questions¨ conceptuals que envolten el camp de l’evolucio´ del llenguatge, principalment aquelles que provenen del ambit` de la lingu¨´ıstica. Contents Abstract iii Resumv Contents vii List of Figuresx List of Tables xi Full List of Abbreviations xiii Acknowledgments xv 1 Introduction1 1.1 Reasons for studying vocal learning in language evolution...... 2 1.2 Two tenets that guide the work in this thesis.............. 4 1.2.1 e notion of vocal learning adopted.............. 4 1.2.2 Doing away with dichotomies.................. 5 1.3 esis Outline............................... 6 2 Language and complexity considerations: e no half-Merge fallacy9 2.1 Introduction................................ 10 2.2 e no half-Merge argument....................... 11 2.3 e no half-Merge fallacy......................... 12 3 Vocal learning: Beyond the contiguum 17 3.1 Introduction................................ 18 3.1.1 e “canonical” list of vocal learners.............. 18 3.1.2 e vocal learning continuum and beyond........... 20 3.2 Limitations of the vocal learning continuum.............. 20 3.2.1 Bidimensionality......................... 21 3.2.2 More on brain wiring....................... 22 3.2.3 Complexity considerations.................... 24 vii viii Contents 3.3 A more permissive view

Load more