Department of Biology, FI-20014 University of Turku, Turku, Finland.
Institute of Estonian and General Linguistics, Jakobi 2, University of Tartu, 51014, Tartu, Estonia.
BMC Evol Biol. 2018 Sep 3;18(1):132. doi: 10.1186/s12862-018-1238-6.
The processes leading to the diversity of over 7000 present-day languages have been the subject of scholarly interest for centuries. Several factors have been suggested to contribute to the spatial segregation of speaker populations and the subsequent linguistic divergence. However, their formal testing and the quantification of their relative roles is still missing. We focussed here on the early stages of the linguistic divergence process, that is, the divergence of dialects, with a special focus on the ecological settings of the speaker populations. We adopted conceptual and statistical approaches from biological microevolution and parallelled intra-lingual variation with genetic variation within a species. We modelled the roles of geographical distance, differences in environmental and cultural conditions and in administrative history on linguistic divergence at two different levels: between municipal dialects (cf. in biology, between individuals) and between dialect groups (cf. in biology, between populations).
We found that geographical distance and administrative history were important in separating municipal dialects. However, environmental and cultural differences contributed markedly to the divergence of dialect groups. In biology, increase in genetic differences between populations together with environmental differences may suggest genetic differentiation of populations through adaptation to the local environment. However, our interpretation of this result is not that language itself adapts to the environment. Instead, it is based on Homo sapiens being affected by its environment, and its capability to adapt culturally to various environmental conditions. The differences in cultural adaptations arising from environmental heterogeneity could have acted as nonphysical barriers and limited the contacts and communication between groups. As a result, linguistic differentiation may emerge over time in those speaker populations which are, at least partially, separated.
Given that the dialects of isolated speaker populations may eventually evolve into different languages, our result suggests that cultural adaptation to local environment and the associated isolation of speaker populations have contributed to the emergence of the global patterns of linguistic diversity.
导致当今 7000 多种语言多样性的过程是几个世纪以来学术界关注的主题。有几个因素被认为有助于说话人群体的空间隔离和随后的语言分歧。然而，它们的正式测试和相对作用的量化仍然缺失。我们在这里关注的是语言分歧过程的早期阶段，即方言的分歧，特别关注说话人群体的生态环境。我们从生物微观进化中采用了概念和统计方法，并将语言内部的变异与同一物种内的遗传变异进行了平行比较。我们在两个不同层面上模拟了地理距离、环境和文化条件以及行政历史差异对语言分歧的作用：在市级方言之间（生物学上，个体之间）和方言群体之间（生物学上，种群之间）。
我们发现地理距离和行政历史在分离市级方言方面很重要。然而，环境和文化差异对方言群体的分歧有显著贡献。在生物学中，种群之间遗传差异的增加以及环境差异可能表明种群通过适应当地环境而发生遗传分化。然而，我们对这一结果的解释并不是语言本身适应环境。相反，它基于智人受到环境的影响，以及其适应各种环境条件的文化能力。环境异质性引起的文化适应差异可能起到非物理障碍的作用，并限制了群体之间的接触和交流。因此，在至少部分分离的说话人群体中，语言分化可能会随着时间的推移而出现。
鉴于孤立说话人群体的方言最终可能演变成不同的语言，我们的结果表明，对当地环境的文化适应以及与之相关的说话人群体的隔离，促成了全球语言多样性模式的出现。
