Oceanic barriers promote language diversification in the Japanese Islands

Good barriers make good languages. Scholars have long speculated that geographical barriers impede linguistic contact between speech communities, and promote language diversification in a manner similar to the process of allopatric speciation. This hypothesis, however, has seldom been tested systematically and quantitatively. Here we adopt methods from evolutionary biology and attempt to quantify the influence of oceanic barriers on the degree of lexical diversity in the Japanese Islands. Measuring the degree of beta diversity from basic vocabularies, we find that geographical proximity and, more importantly, isolation by surrounding ocean, independently explains a significant proportion of lexical variation across Japonic languages. Further analyses indicate that our results are neither a byproduct of using a distance matrix derived from a Bayesian language phylogeny nor an epiphenomenon of accelerated evolutionary rates in languages spoken by small communities. Moreover, we find that ...地理屏障愈完备，语言多样性愈显著。长期以来，学者们一直推测，地理屏障会阻碍不同语言社群间的语言接触，并以类似于异域成种（allopatric speciation）的过程推动语言多样化。然而，这一假说极少得到系统性与定量性的验证。本研究借鉴进化生物学的研究方法，尝试量化海洋屏障对日本列岛诸语言词汇多样性程度的影响。我们基于基础词汇表测算β多样性（beta diversity）指数后发现，地理邻近性，以及更为关键的周边海洋所带来的隔离效应，能够独立解释日本语系（Japonic languages）诸语言间大量的词汇变异。进一步分析表明，本研究结果既非源于基于贝叶斯语言系统发育（Bayesian language phylogeny）所构建的距离矩阵的附带效应，也并非小型社群所使用语言的进化速率加快所产生的副现象。此外，我们发现……