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

Area of Science:

• Cognitive Science
• Evolutionary Biology
• Linguistics

Background:

• The Chomskyan evolutionary conjecture proposes language arose instantaneously in humans via a single mutation.
• This hypothesis has lacked formal evolutionary dynamics analysis.
• It posits emergence and fixation of a single mutant with syntactic Merge ability in a small population (~15,000) with high fitness advantage.

Purpose of the Study:

• To formally analyze the evolutionary dynamics implied by the Chomskyan single-mutation hypothesis for language origin.
• To determine the probability of a single mutation leading to language evolution versus multiple mutations.
• To assess if evolutionary reasoning supports a single-mutant theory of language.

Main Methods:

• Combined diffusion analysis and extreme value theory to create a probabilistic model of evolutionary dynamics.
• Examined the probability of macro-mutations occurring and reaching fixation in a population.
• Compared the likelihood of single large-effect mutations versus multiple small-to-medium effect mutations.

Main Results:

• While a macro-mutation is more likely to fix if it occurs, it is a priori much less probable than multiple smaller mutations.
• The most probable evolutionary scenario involves the accumulation of a moderate number of mutations with medium fitness effects.
• This precise probabilistic analysis of mutation occurrence and fixation has not been previously applied to language evolution.

Conclusions:

• The study's findings cast doubt on the Chomskyan single-mutant hypothesis for language origin.
• Evolutionary reasoning does not independently support a single-mutant theory of language.
• Gradual accumulation of multiple genetic changes is a more likely evolutionary pathway for language.