Do principles of language processing in the brain affect the way grammar evolves over time or is language change just a matter of socio-historical contingency? While the balance of evidence has been ambiguous and controversial, we identify here a neurophysiological constraint on the processing of language that has a systematic effect on the evolution of how noun phrases are marked by case (i.e. by such contrasts as between the English base form she and the object form her). In neurophysiological experiments across diverse languages we found that during processing, participants initially interpret the first base-form noun phrase they hear (e.g. she…) as an agent (which would fit a continuation like … greeted him), even when the sentence later requires the interpretation of a patient role (as in … was greeted). We show that this processing principle is also operative in Hindi, a language where initial base-form noun phrases most commonly denote patients because many agents receive a special case marker ("ergative") and are often left out in discourse. This finding suggests that the principle is species-wide and independent of the structural affordances of specific languages. As such, the principle favors the development and maintenance of case-marking systems that equate base-form cases with agents rather than with patients. We confirm this evolutionary bias by statistical analyses of phylogenetic signals in over 600 languages worldwide, controlling for confounding effects from language contact. Our findings suggest that at least one core property of grammar systematically adapts in its evolution to the neurophysiological conditions of the brain, independently of socio-historical factors. This opens up new avenues for understanding how specific properties of grammar have developed in tight interaction with the biological evolution of our species.

The animate–inanimate distinction is of crucial importance cognitively, and animacy has been known to influence language comprehension. However, little is known about the role of animacy in verb agreement processing. The present study employed event-related brain potentials to examine whether the gender agreement of the verb with animate (natural gender) and inanimate (grammatical gender) subject nouns reveal similar or different processing mechanisms in Hindi. Critical stimuli were intransitive sentences of the form subject–verb–aux. Subject nouns were either animate or inanimate, and the verb either showed correct gender agreement or violated it. The violation of gender agreement with animate subjects evoked a P600 effect, whereas gender agreement violation with inanimate subjects revealed a long-latency N400-like effect. The result suggests that different underlying mechanisms are involved in the computation of gender agreement with animate and inanimate arguments in Hindi, illustrating the crucial role that animacy plays in verb agreement processing.

The study reported here was conducted to investigate the neurophysiological correlates of processing two types of subject experiencer verbs, namely mental experiencer verbs and physical experiencer verbs in Malayalam, a South Dravidian language. Event-related brain potentials (ERPs) were recorded as twenty-eight first-language speakers of Malayalam read intransitive sentences with the two types of experiencer verbs. Critical stimuli were either fully acceptable, whereby the subject case matched the requirements of the verb, or unacceptable, whereby the subject case violated the requirements of the verb. A linear mixed-models analysis confirmed negativity effects in the time window 400–800 ms for mental and physical experiencer verbs. Post-hoc analyses revealed that the negativity peaked relatively early for mental experiencer verbs, whereas relatively late for physical experiencer verbs. Further, the sentence-final acceptability of trials modulated the ERPs in non-anomalous conditions but not in violation conditions, and this modulation qualitatively differed between mental and physical experiencer verbs. These results suggest that, whilst a qualitatively similar mechanism is involved in the processing of both kinds of experiencer verbs, subtle but robust differences are inherent in processing mental versus physical experiencer verbs in Malayalam.