The genetically-minded Moderns of the 1930s felt they were facing a grave demographic crisis : why where there so few Ubermensch and so many undermensch: why so few Cedars and so much hyssop ?
In other words, why on earth were there so many beetles, defectives and useless mouths ?
Not believing in a Supreme Being, at least not believing in any Being Superior to themselves, they had to blame the Iron Laws of Nature and Evolution for this un-natural natural fondness for things weak and foolish.