 According to Korotayev, a systematic acceptance of parallel-cousin marriage took place when Islamization occurred together with Arabization.This research further led to the discovery of the so-called Afrasian Instability Zone.Korotayev has made a special contribution in this field by detecting principal trends in the evolution of Yemeni cultures through application of quantitative methods to the analysis of mass epigraphic sources in the Sabaic language.