Detecting evolutionary forces in language change

Abstract

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.

Quantifying the dynamics of topical fluctuations in language

“…These results clearly show that topical fluctuations can be expected to explain a significant amount of change in word frequencies, which one might otherwise be tempted to attribute to other processes, such as selection-be it due to content or formal biases, sociolinguistic prestige, phonological neighborhood effects (e.g. Newberry et al, 2017), or other changes in the transmission biases of speakers (cf. Enfield, 2014).…”

“…It is widely agreed that not all language change is necessarily caused by selection by speakers for certain variants or utterances, but also involves random processes (i.e., drift, or neutral evolution) (Andersen, 1987;Blythe, 2012;Hamilton et al, 2016a;Jespersen, 1922;Newberry et al, 2017;Reali and Griffiths, 2010;Sapir, 1921). Naturally, this should be taken into account in a diachronic study of language.…”

“…Adopting this framework, Newberry et al (2017) claim to show that tests developed in genetics for distinguishing drift and selection of variants in biological evolution can be applied to frequency time series of competing linguistic variants. In particular, they apply the Frequency Increment Test (Feder et al, 2014), and do so on three test cases of changes in the grammar of the English language.…”

“…Adjusting for topics has the potential to be useful in carrying out more objective tests of linguistic selection (cf. Newberry et al, 2017), by controlling for the topical-cultural element. Figure 2 illustrates the results of the aforementioned decomposition operation on four words with different frequency trajectories.…”

Fading of collective attention shapes the evolution of linguistic variants

“…The competition of subjunctive forms seems to be dominated by a general preference for the form -ra across the Spanish speaking countries (23), which is indeed manifested in the fact that the institutional enforcement produced just a local perturbation in the trend of increasing dominance of -ra. Forces that drive selection to one of the alternatives in competition have been explored, and include social and cognitive factors, as well as phonological and biophysical factors (3,24). Although the forces underlying the preference for -ra rest unknown, the dynamics that drive speakers towards the preferred form are modulated by collective behaviors such as the ones analyzed in the present work.…”