Evolutionary Biology from Concept to Application

pp 197-207

Nothing in Medicine Makes Sense Except in the Light of Evolution: A Review

  • Bernard SwynghedauwAffiliated withHôpital Lariboisière, Centre de Recherches Cardiovasculaires de 1’INSERM

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Applying evolutionary biology to medical problems is surprisingly new and still absent from medical as well biological teaching, despite the fact that “nothing in biology makes sense except in the light of evolution” (T. Dobzhansky in Am. Biol. Teach. 35:125, 1973), and biology is the basis of medicine. Evolutionary medicine takes the view that contemporary diseases are related to incompatibility between the environment in which humans currently live and the conditions under which human biology evolved and genomes have been shaped by a different environment during biological evolution. Human activity has recently acutely modified the environmental conditions in which all living beings live. The main result is a spectacular increased lifespan and pronounced change in the medical landscape. The concept of evolutionary medicine applies to every disease state. From an epidemiological viewpoint, the simultaneous increased incidence in both autoimmune (type 1 diabetes, Crohn’s disease, etc.) and allergic (asthma, childhood allergy, etc.) diseases is inversely related to the drop in infectious diseases. The so-called hygiene hypothesis is now solidly established and its mechanism is well documented. It involved both a strong genetic component and a dysregulation of the immune system with a main role attributed to interleukin-10. The conflict resulting from the free availability of food and salt and the remaining fat- and salt-retaining genes is now considered as a major determinant of the rising epidemic incidence of obesity, arterial hypertension and type 2 diabetes. The so-called metabolic syndrome is a summary of these different components and represents a major goal for contemporary preventive medicine. For example, genome-wide association studies have currently identified at least nine genes which are significantly associated with type 2 diabetes. Cancer may be viewed as an accelerated form of evolution at the level of cancer cells. About one third of the hundreds of mutations which have been identified so far in cancers are subject to an evolutionary pressure with a nearly doubling of the nonsynonymous to synonymous substitutions ratio. The genome-environment relationship is a major paradigm for a biologist. It is equally important in medicine, and diseases can now be ascribed as a threshold on a norm reaction curve that depends on a given genotype.