Are modern environments really bad for us?: revisiting the demographic and epidemiologic transitions.

It is a common assumption that agriculture and modernization have been detrimental for human health. The theoretical argument is that humans are adapted to hunter-gatherer lifestyles, and that the agricultural and "modern" environments are novel and hence likely to be detrimental. In particular, changes in nutrition, and population size and distribution with the adoption of agriculture, are considered to increase the risk of infectious disease mortality. Similarly, changes due to modern lifestyles, notably changes in nutrition, smoking, exercise, and stress, are thought to be associated with an increased risk of degenerative disease mortality in the industrial environment. This paper reviews the available literature on the history and prehistory of total mortality (the demographic transition) and cause of death (the epidemiologic transition), and finds that neither agriculture nor modernization is associated with increases in mortality, i.e., declines in health. First, mortality does not appear to have increased during the transition to agriculture, or during the early phases of the industrial revolution. Clearly, infectious diseases have declined with modernization. Second, the empirical data, when uncorrected for misclassification of cause of death, do suggest an increase in degenerative disease mortality, at least until the mid 20th century, when these causes of death clearly began to decline. All studies that correct for misclassification of cause of death, however, find that the general decline in degenerative disease mortality began much earlier, perhaps as early as the 1850s in the developed countries. This is about the same time that infectious disease mortality began to decline in these countries. The exception is neoplasms, which increased with modernization until quite recently. Part of the increase in neoplasms may be attributable to increases in smoking during the course of modernization. Nevertheless, the overall risk of degenerative disease mortality appears to have declined with modernization. The fact that the decline in the risk of infectious disease mortality, and the decline in risk of degenerative disease mortality, are largely coordinated suggests that the causes of both declines may be related. Historical trends in morbidity, and potential causes of the decline in infectious and degenerative disease mortality, are briefly considered.