Language Impairments in ASD Resulting from a Failed Domestication of the Human Brain

Abstract

Autism spectrum disorders (ASD) are pervasive neurodevelopmental disorders entailing social and cognitive deficits, including marked problems with language. Numerous genes have been associated with ASD, but it is unclear how language deficits arise from gene mutation or dysregulation. It is also unclear why ASD shows such high prevalence within human populations. Interestingly, the emergence of a modern faculty of language has been hypothesized to be linked to changes in the human brain/skull, but also to the process of self-domestication of the human species. It is our intention to show that people with ASD exhibit less marked domesticated traits at the morphological, physiological, and behavioral levels. We also discuss many ASD candidates represented among the genes known to be involved in the “domestication syndrome” (the constellation of traits exhibited by domesticated mammals, which seemingly results from the hypofunction of the neural crest) and among the set of genes involved in language function closely connected to them. Moreover, many of these genes show altered expression profiles in the brain of autists. In addition, some candidates for domestication and language-readiness show the same expression profile in people with ASD and chimps in different brain areas involved in language processing. Similarities regarding the brain oscillatory behavior of these areas can be expected too. We conclude that ASD may represent an abnormal ontogenetic itinerary for the human faculty of language resulting in part from changes in genes important for the “domestication syndrome” and, ultimately, from the normal functioning of the neural crest.

Evaluating the self‐domestication hypothesis of human evolution

“…The encompassing nature of the HSD hypothesis makes it what some would call an “umbrella hypothesis”: it simultaneously explains multiple traits, with a single mechanism driving a cascade of events. Accordingly, it has received prominent media and popular science attention, and several recent publications have cited it as firmly established and used it to interpret aspects of brain evolution in humans . Overall, therefore, the HSD hypothesis deserves serious scrutiny as a likely candidate to explain patterns in human evolution.…”

“…Accordingly, it has received prominent media and popular science attention, [21][22][23] and several recent publications have cited it as firmly established and used it to interpret aspects of brain evolution in humans. 24,25 Overall, therefore, the HSD hypothesis deserves serious scrutiny as a likely candidate to explain patterns in human evolution.…”

Autism and Williams syndrome: dissimilar socio-cognitive profiles with similar patterns of abnormal gene expression in the blood

“…Finally, the HPA axis (a major neuroendocrine system resulting from the interaction between the hypothalamus, the pituitary gland, and the adrenal glands) comes into play here, because of its involvement in stress response---particularly, the response to cortisol in the amygdala, the PFC, and the hippocampus--all of them areas implicated in situations of fear and social stress (see Martens et al, 2008;Dedovic et al, 2009;Lense and Dykens, 2013;Bitsika et al, 2015). Both ASD and WS individuals have been shown to exhibit interrupted HPA axis function (Spratt et al, 2012;Jacobson, 2014;Benítez-Burraco et al, 2016;Niego and Benítez-Burraco, 2019, among many others). This might explain in part the prevalence of anxiety in the two disorders, although as mentioned above, the anxiety generally seems to happen in separate arenas for each group: social in ASD and non-social in WS (see also Dykens, 2003;Graham et al 2005;Rodgers et al, 2012;Lense and Dykens, 2013).…”

Abnormal features of human self-domestication in bipolar disorder

“…In further support of this view, regions positively selected in modern humans compared to extinct hominins are enriched in candidate genes for domestication in mammals (Theofanopoulou et al, 2017). Interestingly, complex genetic conditions involving cognitive deficits, behavioral anomalies, and abnormal socialization patterns, like SZ and ASD, are characterized by abnormal presentations of traits associated with (self-)domestication; moreover, candidate genes for domestication are overrepresented among the candidates for these conditions and/or exhibit altered expression profiles in the brains of affected people (Benítez-Burraco et al, 2016; Benítez-Burraco et al, 2017; Benítez-Burraco, 2020b). But the same pattern holds in conditions with a neat molecular etiology, like WS, as genes outside the affected genomic region that are differentially-expressed in patients are likewise enriched in candidates for domestication (Niego and Benítez-Burraco, 2019).…”