Sound production learning across species: beyond the vocal learning dichotomy

• Autores: Pedro Tiago da Silva Gonçalves Martins
• Directores de la Tesis: Cedric Boeckx (dir. tes.), Bridget Samuels (codir. tes.)
• Lectura: En la Universitat de Barcelona ( España ) en 2020
• Idioma: español
• Tribunal Calificador de la Tesis: Adriano Lameira (presid.), Faustino Diéguez Vide (secret.), Andrea Ravignani (voc.)
• Programa de doctorado: Programa de Doctorado en Ciencia Cognitiva y Lenguaje por la Universidad Autónoma de Barcelona; la Universidad de Barcelona y la Universidad Rovira i Virgili
• Materias:
  • Ciencias de la vida
    • Biología animal (zoología)
      • Comportamiento animal
    • Biología humana
      • Genética humana
    • Fisiología humana
      • Fisiología del lenguaje
    • Biología vegetal (botánica)
  • Lingüística
    • Teoría lingüística
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• Resumen

  • All humans have language. This capacity is a complex biological trait whose evolu­tion is currently an active research topic, especially in recent years. This thesis is an attempt at contributing to this enterprise in two ways, from different angles. Toe first one is a critical assessment of a prominent theory oflanguage evolution, whereby the "core properties oflanguage" can be reduced to a single computational operation, for­mally irreducible, which evolved suddenly as a result of a single genetic mutation. Toe 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.

    Chapter 2 identifies a fallacious line of argument associated with the aforemen­tioned 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. This argument is named here the "no nalf-MERGE" fallacy. After a summary of independent reasons to doubt this hypothesis for how language evolved, it is shown why the argument is biologically untenable in the first place. This chapter lends support to the idea that language evolved gradually.

    Toe greater part of this thesis (chapters 3 and 4) focuses on vocal learning. Vo­cal learning, the capacity to modify auditory output on the basis of experience, is displayed by several species, across different families. In humans, it is crucial for speech. This thesis looks at vocal learning in two ways, by first offering an extension to the Vocal Learning Continuum, an influential framework, and secondly by using genomic information in the human lineage to suggest that vocal learning could have been present in at least sorne of our ancestors, narrowing the gap between them and modern humans regarding language components.

    Toe 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 estab­lishing 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 the whole behavioral spectrum of this phenotype. In chapter 3. after identifying and assessing these limitations, by pointing out conceptual and empirical problems, an extension to the framework is offered, called the Vocal Learning Contiguum, which eschews reliance on particular brain circuits and behaviors, favoring a broader per­spective and welcoming more factors as sources of variation across species.

    Chapter 4 explores a link between the SRGAP2 gene and the emergence of vocal learning in the Horno lineage. SRGAP2C, a duplication of this gene found in Nean­derthals 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 effect on axon guidance and the formation of a cortico-laryngeal connection associated with the human vocal learning circuit.

    Toe thesis is complemented by a series of appendices that del ve in more detail into sorne conceptual issues surrounding the field of language evolution, namely those coming from linguistics.