Understanding world-wide patterns of language diversity has long been a goal for philosophers, linguists, and evolutionary scientists. Research over the past decade has suggested that linguistic diversity may result from differences in the physical and social environments in which languages evolve. Specifically, cross-linguistic and historical analyses showed that the structure of languages spoken in exoteric societies is different from the structure of languages spoken in esoteric societies (e.g., Lupyan & Dale, 2010; Meir et al., 2012; Nettle, 2012; Trudgill, 2009; Wray & Grace, 2007). In particular, it has been argued that increased population size, sparser community structure and higher proportion of adult L2 learners in the community lead to morphological simplification. However, these three community properties are typically confounded in the real world, making it hard to evaluate their separate contribution to this pattern of variation. In this talk I will present results from three studies in which we examine the live formation of new languages created in the lab by different micro-societies, which differ in their size or in their network connectivity. This is the first experimental demonstration for the unique and causal role of community size and network structure in the emergence of linguistic structure.