Human Self-domestication and Language Evolution: Focusing on Disorders
Year: 2022
Type: dissertation
Abstract: The objective of this doctoral thesis is to contribute to the current discussion of the origins \nof language in our species. Various hypotheses have been proposed to explain this conundrum, \nmany of them with antithetical views. The framework adopted in this thesis, and the \nfundamental basis of the investigation conducted therein, is the human self-domestication \nhypothesis. According to this hypothesis, specific characteristics of the human phenotype are a \nresult, in part, of a process similar to that experienced by domesticated animals. The fact that \nmany domesticated animals share common traits, known as the ‘domestication \nsyndrome’ (DS) has led researchers to hypothesize that these cognitive, behavioral, and \nphysical traits are the result of sexual selection of individuals with lower levels of aggression, \nin response to changes in a variety of environmental factors. One consequence of selfdomestication, \naccording to this hypothesis, is the creation of a ‘cultural niche’, that is, a \nsociocultural environment that allows for the complexification of language via a cultural \nmechanism (Thomas and Kirby, 2018; Benítez-Burraco and Progovac, 2020). In this view, \nhuman language (particularly, languages used and spoken currently) can be seen as not only \nthe product of biological factors, but also of advanced cultural aspects that characterise us as a \nspecies, which of course are also brought about by the same biological factors that shape \nlanguage. This thesis is centered on the more variable aspects of human selfdomestication; \nsince self-domestication is thought to be the result of physical changes \nrelated to control of aggression, it stands to reason that factors which favor prosocial behavior \nalso heighten traits associated with self-domestication, and vice versa. Because more recently \nevolved traits are more vulnerable to ontogenetic damage, neurodevelopmental disorders \nprove to be key areas of study. A fundamental objective of the thesis is to determine \nthe extent to which features of self-domestication are altered in disorders related to \natypical or impaired socialization, and how this may contribute to the current \nunderstanding of language evolution. In order to do this, two main disorders were selected: \nWilliams Syndrome (WS) and Autism Spectrum Disorders (ASD), which have \ntraditionally been considered to represent opposite extremes when it comes to social \nbehavior, with individuals with ASD exhibiting diminished traits of self-domestication \n(see Benítez-Burraco et al., 2016 for a discussion), and individuals with WS seemingly \nexhibiting exaggerated traits of self-domestication. The first article of this thesis (Niego and Benítez-Burraco, 2019) focuses on WS, with the \nmain goal of discovering whether or not this assumption about exaggerated DS traits is true, \nand if the anecdotal evidence suggesting so can be substantiated with research. The \nresearch conducted for this article supports the fact that many traits of human self-domestication are indeed exaggerated in people with WS. In addition, various candidate genes \nfor domestication in mammals are found to be significantly dysregulated in the blood of \npeople with WS, suggesting that the WS deletion region may contain genes which are involved \nin the self-domesticated phenotype and that these genes affect the characteristic traits of WS. \nOnce this characterization of ASD and WS as hypo- and hyper-domesticated conditions was \nestablished, the second and third articles of this thesis (Niego and Benítez- Burraco, 2020; \nNiego and Benítez-Burraco, 2021a) aimed to determine to what extent these conditions can be \nconsidered as opposite to each other in the sociocognitive realm. The fundamental reason for \nthis was to determine if their opposite manifestations of the self-domestication syndrome affect \nthe cognitive and social/behavioral phenotypes of both disorders. Article Two (Niego and \nBenítez-Burraco, 2020) concluded that ASD and WS cannot be considered to be opposites— \nneither in the phenotypical sense nor in the neurobiological sense. The third article (Niego and \nBenítez-Burraco, 2021a) extended this conclusion to the genetic realm, since a significant \noverlap was found between differentially expressed genes in the blood of ASD and WS. The \naim was to investigate whether there are also quantitative differences at the phenotypic level \nwhich could be attributed to this genetic overlap. The results of both articles suggest that the \ncase of ASD and WS is too complicated to explain these two disorders as opposite ends of a \nspectrum; both ASD and WS are not static conditions, but rather exist on a continuum, of \nwhich neurotypical people are also a part. The last two articles that make up the thesis, \narticles four and five (Niego and Benítez- Burraco, 2021b; Niego and Benítez- Burraco, \n2021c) analyze feralization, a seemingly opposite process to domestication, and its impact on \ncommunicative capacity. Feralization is the process by which a domesticated animal returns to \na wild-like environment. Understanding the extent to which feralization represents a genuine \nreversal of domestication and to what extent it can be seen as simply an adaptation to \nenvironment can aid in understanding the limits of the variation displayed in the selfdomesticated \nphenotype, both in neurotypical populations and in disorders. Article Four \n(Niego and Benítez-Burraco, 2021b) concluded that feralization does not in fact represent a \ncomplete reversal of domestication, but rather that certain physical, behavioral, and \nneurobiological traits revert to some extent. This investigation pointed to the fact that only a \nlimited number of genes are involved in both feralization and domestication, and these genes \ncan be considered to be promising candidates when it comes to explaining the sensitivity \nof self-domestication to environmental effects. Article Five (Niego and Benítez-Burraco, \n2021c) sought to apply the conclusions derived from the previous article to humans, in \nparticular, to clarify to what extent our characteristic sociocognitive traits (resulting from \nhuman self-domestication) are expected to revert as the result of genetic or environmental \nchanges. In order to do this, Article Five made use of various lists of traits garnered from \nliterature on feral animals with characteristics of individuals with ASD–a sociocognitive disorder known for its genetic origin– as well as individuals with Reactive Attachment \nDisorder (RAD) –a sociocognitive disorder known for its environmental origin. Given the \nprincipal objective of this thesis, special attention was paid to problems concerning language \nand communication in all of the groups which were studied.
Source: idUS (Universidad de Sevilla)
Author: Niego, Amy
Language: English
Subfield: Cultural Studies
Field: Social Sciences
Domain: Social Sciences
Open Access status: green
OpenAlex ID: W7057188696