What accounts for the vast diversity in the world’s languages? We explore one possibility: languages adapt to their linguistic environment (Linguistic Niche Hypothesis; Lupyan & Dale, 2010). Recent studies have found support for this hypothesis through correlations between aspects of the environment and linguistic structure. We synthesize this previous work and find that languages spoken in cold, small regions tend to be more complex across a range of linguistic features. We also test a novel prediction of the Linguistic Niche Hypothesis by examining the learnability of languages for first-language, child learners.