Evolving a definition of disease

Koch and Pasteur provided modern medicine with its primary model of disease – that it has a specific and organic cause. Treatment is generally developed from an understanding of that agent of causation. Generations of medical students have been taught the causes of disease in their pathology classes: genetic, infection, trauma and so on. But for some situations such a model is inadequate. The boundaries between normality and abnormality blur, and can be situational and dependent on when and where an individual lives. Persistence of intestinal lactase function was the co-evolutionary outcome when groups of Homo sapiens started herding cattle and using their milk for food