Here is an aspect of Islam that I had not been particularly aware of: 1400 years of Inbreeding Inbreeding apparently has the dual effect of diminishing the viability of the inbred population and simultaneously increasing the likelihood of a beneficial mutation if natural selection is operative within the inbred population. Humans are noted for their disinclination to lose children to the working of natural selection. Medical intervention is the usual response to an imperfect child. That's very humane, but it works directly against the evolution of the human species. And the smaller the subject group the more radical the effect. If marriage to non-Muslims is forbidden, and marriage between first cousins is permitted, there are only a few ways that Islamics can avoid inbreeding themselves to extinction: 1) Start destroying defective Muslim babies, in imitation of (or as a working of) Natural Selection. 2) Increase the number of Muslim women by raping them ten times each, and then marrying them. 3) Conquer the world, and make Islam the only religion. The third option seems to be the only practical course in the long run. So far, Islam has made considerable progress in that direction. At some point the Muslim population will become so large that it will become genetically viable, and inbreeding will no longer be a dignificant concern. In some areas, such as India, that point may have already been reached. Wikipedia sez: Inbreeding - Wikipedia, the free encyclopedia Scrolling down to the "Humans" section. the part about "Prevalence" brings to light some interesting figures. I note that India is not included in them.