Language Evolution and Computation Bibliography

Both language and genes evolve by transmission over generations with opportunity for differential replication of forms. The understanding that gene frequencies change at random by genetic drift, even in the absence of natural selection, was a seminal advance in evolutionary biology. Stochastic drift must also occur in language as a result of randomness in how linguistic forms are copied between speakers. Here we quantify the strength of selection relative to stochastic drift in language evolution. We use time series derived from large corpora of annotated texts dating from the 12th to 21st centuries to analyse three well-known grammatical changes in English: the regularization of past-tense verbs, the introduction of the periphrastic ‘do’, and variation in verbal negation. We reject stochastic drift in favour of selection in some cases but not in others. In particular, we infer selection towards the irregular forms of some past-tense verbs, which is likely driven by changing frequencies of rhyming patterns over time. We show that stochastic drift is stronger for rare words, which may explain why rare forms are more prone to replacement than common ones. This work provides a method for testing selective theories of language change against a null model and reveals an underappreciated role for stochasticity in language evolution.

This dissertation advances our understanding of the roles played by pragmatic and grammatical competence in theories of language change by using mathematical and statistical methods to analyze the cross-linguistic change in the expression of negation known as Jespersen's cycle. In the history of Middle English this change is characterized by two transitions: from pre-verbal ne to an initially emphatic embracing ne...not; from embracing ne...not to post-verbal not. This description conflates two often related process: the formal cycle describes changes in the forms of negation available and consists of the transitions from pre-verbal to embracing to post-verbal negation; the functional cycle describes changes in how forms are used to signal meaning and consists of the transition from pre-verbal to embracing negation. Using tools from evolutionary game theory, we show that the functional cycle can be explained by limits on our pragmatic competence. The incoming embracing form is initially restricted to negating propositions that are common information between interlocutors. But, experimental evidence shows that speakers have difficulty in distinguishing common and privileged information. Speakers use the initially restricted form in more and more contexts that are less and less closely tied to the discourse, and it undergoes a kind of informational bleaching. Applying statistical methods developed in population genetics, we show that grammatical competence, and the process of acquisition through which it is formed, predict stability rather than change in both transitions of the formal cycle unless the observed transitions are the result of the accumulation of small random changes akin to genetic drift in finite populations. We show that we can reject this possibility in the first transition of the formal cycle, but not in the second. The possibility of random change in the second transition of the formal cycle offers some insight into the varying amount of time it takes across languages. The main contribution of this dissertation is demonstrating the need for articulated models of both pragmatic and grammatical competence in explanatory theories of language change, while also offering a set of tools and methods for analyzing different factors in historical corpora. https://repository.upenn.edu/edissertations/1578