But, interestingly, many Darwinists were not willing to live with complete moral relativism. They still retained one fixed point of reference—the process of evolution itself. Since morality arose through evolution, they argued that the purpose of morality is to advance the evolutionary process. They thereby imported the nineteenth-century cult of progress into evolutionary theory. The problem with this is that it presupposed that some forms of morality are “better” than others. But, of course, Darwinism provided no basis to consider some form of morality “better” than any other, or for that matter, it gave no reason to think that morality was “better” in any real sense than immorality. Yet most used morally charged language quite freely, apparently oblivious to the contradiction this entailed.
Those Darwinists who made the evolutionary process the new criteria for morality radically altered the way that people thought about morality. Since they generally affirmed that good health and intelligence were key factors in the upward march of evolution, improving physical vitality and mental prowess—especially of future generations—became the highest moral virtue. The greatest sin was to contribute in some way to the decline of physical life or intellectual ability. This kind of evolutionary ethics flew in the face of Christian morality, in which one’s health, vitality, and mental faculty play no role in determining moral or immoral behavior. While Christian morality demands a relationship of love toward God and one’s neighbors, which involves self-sacrifice, evolutionary ethics focused on breeding better humans, even it if meant sacrificing other people in the process."
Richard Weikart, From Darwin to Hitler, pg.229-230