The Role of the Immune System from an Evolutionary Perspective
Résumé
”Nothing in Biology makes sense, except in the light of evolution.” This famous citation of Theodosius Dobzhansky also underlies the integrative field of evolutionary medicine, which faces the challenge to combine (patho-)physiological mechanisms with evolutionary function. Here we introduce a concept from the study of animal behaviour, which are the four questions of Tinbergen that consider 1) the ontogeny of an individual describing its development, 2) its physiological machinery, which 3) has fitness consequences influencing 4) the evolutionary history (phylogeny) of future generations. It is shown how this concept can be applied to infectious disease and to chronic inflammatory systemic diseases. Evolutionary medicine takes lifetime reproductive success into account. The hypothesis to be tested is that mechanisms underlying a disease in old age might have higher fitness benefits in the pre-reproductive and / or reproductive life history stage. We emphasize that our human aim is not to increase evolutionary fitness but to reduce suffering and costs of public health. Thus, medical research might be most successful in diseases that have no lifetime fitness cost, as otherwise evolution would already have acted against it. Importantly, while no selection pressure existed to favour physiological mechanisms acting against such diseases, such mechanisms might become available via biomedical research. We conclude that for a comprehensive understanding of the pathophysiology of a disease, its fitness consequences and its evolutionary history should be considered. The special situation of the immune system and chronic inflammatory systemic diseases is highlighted.
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