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Department of Health and Exercise Science Colorado State University Fort Collins, CO 80523 Email: cordain{at}cahs.colostate.edu
Dear Sir:
We appreciated and enjoyed Walker's constructive comments and interesting insights and agree with many, but not all, of his conclusions. Numerous epidemiologic data support the notion that increasing Westernization and industrialization in human populations is associated with a greater incidence of chronic degenerative diseases. It is almost axiomatic that changes in diet and activity levels initiated by Westernization and industrialization are largely responsible for these health disorders. As human societies stray farther and farther from the original environmental conditions (both diet and exercise) for which our present genome was selected, it is not unexpected that ill-health effects should emerge (1, 2).
We have little doubt that some, but not all, lifestyle characteristics of rural Africans and many of the world's other less industrialized people could serve as a model to benefit the health and well-being of Western populations. However, the reason certain of these lifestyle variables are advantageous is that they are consistent with those of Stone Age hunter-gatherers that in turn represent the lifestyle characteristics for which our species is genetically adapted. High levels of physical activity are required of both hunter-gatherers (2) and rural Gambian subsistence farmers (3) and similarly may provide both of these groups with protection from degenerative disorders and disease. However, the proximate mechanisms of exercise's therapeutic effect are not specifically intrinsic to subsistence farming but, rather, stem ultimately from the rigors and selective pressures dictated by the physical requirements of the hunter-gatherer lifestyle that shaped the present human genome over >2 million years of evolutionary experience. Similarly, it was found that increased dietary intakes of n-3 fatty acids may provide protection from chronic disease in highly industrialized societies such as Japan (4) and in partially Westernized hunter-gatherers such as the Inuit (5). The ultimate evolutionary reason these fatty acids afford protection for these diverse populations is based on our species' genetically determined requirement for them, which in turn was shaped by the environmental selective pressures that fashioned the present human genome. By examining the original environmental conditions for which our present genome was selected during the Paleolithic Era (the Old Stone Age, lasting from 2.6 million y ago until the agricultural revolution 10000 y ago), it is possible to gain insight into optimal lifestyle characteristics that may be of therapeutic value for modern populations experiencing degenerative disorders.
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