Hunting Monsters: Modelling Language Survival

"Now, of course, the fellows producing this model are physicists and they are not directly familiar with the socio-political factors that can strengthen or weaken a language, though they did attempt to factor some of these into their results. Their model nevertheless produced some interesting findings. They reckoned that there are three factors that allow two languages to coexist indefinitely in an area. Firstly, there needs to be a significant number of speakers of each language there. Secondly, the languages need to be somewhat similar. And thirdly, there needs to be a large bloc of people who can speak both languages. Their model is apparently fairly good at retrospectively predicting the historical data on the relative strength of Spanish and Galician in northwest Spain. The last requirement is being presented as the most surprising one, but I was struck by their model's suggestion that the two co-existing languages need to be somewhat similar."