From a friend:

Perhaps another way of looking at this issue is to ask whether or not faith is a universal human condition. There is a school of thought, based on Luther, that suggests faith is universally present in each human person. It is even suggested that it has natural stages that can be correlated with other psychological and sociological stages of human development (As in James Fowler’s “Stages of Faith”).

If this suggestion has any merit then Luther’s claim that salvation comes through faith alone may have universal application.