A serial founder effect model of phonemic diversity based on phonemic loss in low-density populations

It has been observed that the number of phonemes in languages in use today tends to decrease with increasing distance from Africa. A previous formal model has recently reproduced the observed cline, but under two strong assumptions. Here we tackle the question of whether an alternative explanation for the worldwide phonemic cline is possible, by using alternative assumptions. The answer is affirmative. We show this by formalizing a proposal, following Atkinson, that this pattern may be due to a repeated bottleneck effect and phonemic loss. In our simulations, low-density populations lose phonemes during the Out-of-Africa dispersal of modern humans. Our results reproduce the observed global cline for the number of phonemes. In addition, we also detect a cline of phonemic diversity and reproduce it using our simulation model. We suggest how future work could determine whether the previous model or the new one (or even a combination of them) is valid. Simulations also show that the clines can still be present even 300 kyr after the Out-of-Africa dispersal, which is contrary to some previous claims which were not supported by numerical simulations.

已有观测表明，当今在用语言的音位（phoneme）数量往往随与非洲的地理距离增加而递减。此前已有一项形式化模型复现了这一观测到的渐变趋势，但该模型需满足两项较强的假设。本文旨在探讨：若采用不同的假设条件，能否为全球音位数量的地理渐变梯度提供另一种解释？答案是肯定的。我们沿袭阿特金森（Atkinson）的研究视角，形式化提出了如下假说：该分布模式或源于反复出现的瓶颈效应与音位丢失过程。在我们的模拟实验中，现代人类走出非洲的扩张进程里，人口密度较低的群体发生了音位丢失现象。我们的研究结果复现了观测到的全球音位数量渐变趋势。此外，我们还观测到了音位多样性的渐变梯度，并通过模拟模型成功复现了这一现象。我们提出了未来研究的可行方向：通过相关工作验证此前的模型、本文提出的新模型（或二者的结合）是否成立。模拟实验还显示，即便在现代人类走出非洲扩张事件发生30万年后，音位数量的渐变梯度依然存在——这与此前一些未得到数值模拟支持的论断相悖。