Evolutionary Dynamics Do Not Motivate a Single-Mutant Theory of Human Language

Abstract

One of the most controversial hypotheses in cognitive science is the Chomskyan evolutionary conjecture that language arose instantaneously in our species as the result of a single staggeringly fortuitous mutation. Here we analyze the evolutionary dynamics implied by this hypothesis, which has never been formalized. The theory supposes the emergence and fixation of a single mutant (capable of the syntactic operation Merge) during a narrow historical window as a result of frequency-independent selection under a huge fitness advantage in a population of an effective size that is standardly assumed to have been no larger than ~15 000 early humans. We examine this proposal by combining diffusion analysis and extreme value theory to derive a probabilistic formulation of its dynamics. Perhaps counter-intuitively, a macro-mutation is much more unlikely a priori than multiple mutations with smaller fitness effects, yet both hypotheses predict fixation with high conditional probability. The consequences of this asymmetry have not been accounted for previously. Our results diffuse any suggestion that evolutionary reasoning provides an independent rationale for the controversial single-mutant theory of language.3 Significance statementIn recent years, Chomsky and colleagues have sought support for their minimalist theory of the language faculty from evolutionary considerations. They have argued for a spontaneous emergence of a mutation conferring an advantage for thought independent of communication. Here for the first time a formalization of this view is offered, and contrasted with a more gradual evolutionary scenario. The outcome of our analysis argues against the Chomskyan view. 4

The Language Origin Paradigms: Conceptual Typologies, Results Accumulation, and Theoretical Perspectives

“…The "language Rubicon" means the qualitative boundary between the communicative systems of animals and human language.6 See the recent criticism in (deBoer et al, 2020).7 Punctuated equilibria which hold that evolutionary transformations took place in sudden, radical steps(Gould & Eldredge, 1977).…”

Loquens : A characterization of “Hunter-Gatherers of Words”

“…We can ask the same question about the evolution of language and its contribution to the human condition: knowing what we know now about human evolution, and in particular having access to high-quality genomes of our closest extant and extinct relatives (Meyer et al, 2012;Prüfer et al, 2014Prüfer et al, , 2017Mafessoni et al, 2020), are there positions along the spectrum of possible hypotheses regarding the evolution of language and cognition that we can safely put aside as wrong or so implausible as not to be worthy of serious consideration? I have argued elsewhere (Boeckx, 2017b;Martins and Boeckx, 2019;de Boer et al, 2020;Boeckx, 2021) that an entire class of evolutionary narratives exemplified by Berwick and Chomsky (2016), which posit one or a few key changes at the level of the genome and the brain that are claimed to have sparked a recent cognitive revolution in our lineage, have lost their initial conceptual appeal because the evolutionary trajectory of our lineage is clearly vastly much more complex than we used to think even just two decades ago. The twists and turns, booms and busts, carefully uncovered over the past decade in (geography/climate-aware) archaeology 1 (Scerri et al, 2014(Scerri et al, , 2018(Scerri et al, , 2019Groucutt et al, 2021;Kaboth-Bahr et al, 2021;Gosling et al, 2022;Foerster et al, 2022), alongside the numerous instances of events gene-flow across species that can be inferred from ancient genomes (Bergström et al, 2021), leave little room for doubt.…”