THERE are probably no biological interactions more complex than those which take place between men and the environment in which they live; yet, in spite of this, it has been customary to consider only quite circumscribed features of human activity—such as the pattern of eating, or the amount of physical activity associated with an occupation—as largely determining whether or not men will develop quite specific diseases, such as atherosclerosis or essential hypertension.
It has also been assumed that one can find populations which are essentially homogeneous with regard to all pertinent aspects of human activity except 1 or 2, and which, therefore, may be used to investigate the specific effects of these specific activities upon specific disease syndromes, without considering other and more complex human activities which might significantly influence the occurrence of many diseases, and which might significantly alter the interpretation of the findings. Having available an unusually
Christenson WN, Hinkle LE. Differences in Illness and Prognostic Signs in Two Groups of Young Men. JAMA. 1961;177(4):247-253. doi:10.1001/jama.1961.73040300003006