Abstract
OBJECTIVE
Medicine does not have a comprehensive theory of health, ill-health, and disease. Its explanations of disease are firmly rooted in pathological anatomy brought about by infection, intoxication, trauma, and mutations in genes. Because medical concepts have been influenced mainly by classical physics, it is mechanistic, materialistic, deterministic, reductionistic, linear-causal, and strongly biased toward proximate explanations of disease. Of late, many thoughtful persons have attempted to provide medicine with a more comprehensive theory that integrates the documented roles of physical, social, environmental, and psychological factors in the etiology and pathogenesis of ill-health and disease (eg, Refs. 1-3).
METHOD
Until very recently (4), no one has clearly pointed out that such a comprehensive theory should be guided by the concepts of evolutionary and organismic biology. Darwin's great theory states that evolution is "driven," but not exclusively so, by natural and sexual selection. Natural selection acts on variants that differ in adaptive capacities. Those capable of adaptation survive to reproduce. Failure to adapt reduces reproductive fitness and success, and leads to injury or death. But this formulation could be expanded to regard ill-health and disease as adaptive failures, whereas health usually may be conceived of as equivalent to adaptive success. Adaptations are determined by many factors-genetic, morphological, physiological, and behavioral. Selective pressures are many and varied. However, social primates are at a selective advantage, and are among the most successful species and varieties. Social behavior (eg, support) seems to enhance the chances of survival and reproductive fitness. Physiological (immunological, metabolic, cardiovascular) and behavioral adaptations are geared specifically for interactions with the environment. Emotions have evolved as ways of matching physiological responses with environmental demands and signaling the organism's state.
RESULTS
This study will review aspects of evolutionary theory that would lead to a unified, integrated theory of health, illness, and disease, and to a clearer taxonomy in medicine.
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