On the other hand, controversial research by Gregory Clark has indicated that social mobility has been consistently low but non-negligible throughout history, and that social mobility was no lower in previous centuries than it has been in recent times [REF].
Genetic studies have suggested that most Jewish congenital diseases arose from genetic drift after a population bottleneck, a phenomenon known as the founder effect, rather than from selective pressure favoring those genes as called for by the Cochran, et al. hypothesis [REF].