Overview: Debating the effect of environment on language
If languages do indeed evolve then they must show the three crucial aspects of an evolving system: variation of traits, inheritance of those traits, and the differential survival—that is selection—of those traits (Lewontin 1970). We know that languages vary (otherwise the fields of linguistic typology and sociolinguistics would be boring). We know that variation is passed through speech communities and inherited from parent language to its daughters (otherwise historical linguistics would likewise be boring). However, whether linguistic traits are selected for is much less clear (Ramsey and De Block 2016). Nor is it clear just where selection might operate (Dediu et al. 2013).