Language Structure Is Partly Determined by Social Structure
Languages having the most speakers — and those that have spread around the world — were found to have far simpler grammars, specifically morphology, than languages spoken by few people and in circumscribed regions. For example, languages spoken by more than 100,000 people are almost six times more likely to have simple verb conjugations compared to languages spoken by fewer than 100,000 people.
Lupyan and Dale call this social affect on grammatical patterns the “Linguistic Niche Hypothesis.” Languages evolve within particular socio-demographic niches. Although all languages must be learnable by infants, the introduction of adult learners to some languages (for example, through migration or colonization) means that aspects of a language difficult for adults to learn will be less likely to be passed on to subsequent generations of learners. The result is that languages spoken by more people over larger geographic regions have become morphologically simpler over many generations.
Gary Lupyan, Rick Dale. Language Structure Is Partly Determined by Social Structure. PLoS ONE, 2010; 5 (1): e8559 DOI: 10.1371/journal.pone.0008559