He believed they all were related to the mismatch of genes and environment. At a genetic level, the individual had a need for a different level of nutrients to promote proper phenotypic function. If that need were not met, the resulting undernutrition would manifest as chronic disease in midlife. This very powerful concept revolutionized our thinking about the origin of age-related diseases. In defending his concept of biochemical individuality in a talk I once heard him give, Dr. Roger Williams said, Nutrition is for real people.
Statistical humans are of little interest.
Everyone in the audience realized he or she had spent years in studying statistical humans but had never seen one in real practice. People are unique. We must treat real people with respect for their biochemical uniqueness. As the father of the physiological definition of the word stress, Dr. Selye opened the minds of both medical professionals and healthcare consumers to the role of the mind in the function of the body. The combination of the physiology of stress and the understanding of the influence of perceived stress on genetic expression serve as a powerful driver for the evolution of molecular medicine.