 Korotayev concludes that, because the communal democracy correlates positively with the supracommunal one, the Christianization of Europe might have contributed to the development of modern democracy by helping to destroy unilineal descent organisation in this region.Islamization, along with an area's inclusion in the 8th-century Arab-Islamic Khalifate (and its persistence within the Islamic world) has been demonstrated by Korotayev to be a strong and significant predictor of parallel cousin (Father's Brother's Daughter – FBD) marriage.He has shown that while there is a clear functional connection between Islam and FBD marriage, the prescription to marry a FBD does not appear to be sufficient to persuade people to actually marry thus, even if the marriage brings with it economic advantages.