Dupanloup de Ceuninck I, Schneider S, Langaney A, Excoffier L
Laboratoire de Génétique et Biométrie, Département d'Anthropologie, Université de Genève, Geneva, Switzerland.
Eur J Hum Genet. 2000 Oct;8(10):750-6. doi: 10.1038/sj.ejhg.5200519.
We present here a quantitative way to assess the impact of language-family boundaries on population differentiation and to evaluate the homogeneity of the genetic processes along these boundaries. Our estimator (delta a) of the impact of the boundary is based on an isolation by distance (IBD) model and measures the added genetic distance between populations located on different sides of the boundary. We compare this statistic with another estimator of group differentiation (F(CT)) computed under an analysis of variance framework that does not assume any particular spatial structure of the populations. Monte Carlo simulations are used to study the behaviour of these statistics under a two-dimensional stepping-stone model. Simulations show that F(CT) can suggest the existence of a frontier when populations only differ because of IBD. This spurious behaviour is much less frequent for the delta a statistic. However, the large variance associated with the delta a statistic, and the fact that it should only be computed in the presence of IBD, may limit the use of this statistic. Overall, the origin and the effect of the boundary is best understood by comparing different statistics and by testing for the presence of IBD on each side of the boundary as well as across the boundary. We illustrate our approach by examining the boundary between Afro-Asiatic and Indo-European populations. These populations are globally genetically differentiated, but the effect of the linguistic boundary on gene flow seems geographically very heterogeneous. This boundary appears to be the result of a secondary contact between two differentiation centres rather than an enhancer of population differentiation.
我们在此提出一种定量方法，以评估语系边界对群体分化的影响，并评估沿这些边界的遗传过程的同质性。我们对边界影响的估计值（δa）基于距离隔离（IBD）模型，并测量位于边界两侧的群体之间额外的遗传距离。我们将这个统计量与在不假设群体有任何特定空间结构的方差分析框架下计算的另一个群体分化估计值（F(CT)）进行比较。蒙特卡罗模拟用于研究这些统计量在二维 stepping-stone 模型下的行为。模拟表明，当群体仅因 IBD 而不同时，F(CT) 可能会表明存在一个边界。对于 δa 统计量，这种虚假行为的频率要低得多。然而，与 δa 统计量相关的大方差，以及它仅应在存在 IBD 的情况下计算这一事实，可能会限制该统计量的使用。总体而言，通过比较不同的统计量，并测试边界两侧以及跨边界是否存在 IBD，可以最好地理解边界的起源和影响。我们通过研究亚非语系和印欧语系群体之间的边界来说明我们的方法。这些群体在全球范围内存在遗传分化，但语言边界对基因流动的影响在地理上似乎非常不均匀。这个边界似乎是两个分化中心二次接触的结果，而不是群体分化的增强因素。
