ABSTRACT
During most of the twentieth century, the “germ theory” model dominated etiological explanations of disease. The prevalent model now, is a “gene model” where new genetic diseases are being discovered or defined, and many common diseases that already existed are being redefined in genetic terms. The concept of genetic disease has not remained stable but has changed from the fairly restricted notion of a disease traceable to a single gene defect with 100% heritability to the present extended usage where it represents common disease and even complex behavioral traits such as alcoholism. HTN, asthma, and coronary heart diseases are all defined as complex multifactorial diseases. These complex diseases are usually the result of long-term, often subtle, gene-environment interactions, such that individual life histories may be as important as population histories in predicting and explaining these traits.
