Evolutionary Approach to Medicine

Marcelo Turkienicz Berlim, MD, Alberto Mantovani Abeche, MD, Department of Gynecology and Obstetrics, Federal University of Rio Grande do Sul, School of Medicine, Porto Alegre, RS, Brazil

South Med J. 2001;94(1) 

In This Article

Abstract and Introduction

A new discipline in the medical field, called Darwinian (or evolutionary) Medicine, has arisen to study how natural selection could shape a machine as complex as the human body without eliminating its vulnerability to diseases. It asserts that systems and organs that form our bodies result from millions of years of evolutionary advances and are designed to survive in order to reproduce. According to this principle, Nature does not strive for complexity or perfection -- it is blind and random. Using the scientific knowledge that has revolutionized biology, Darwinian Medicine seeks to provide an explanation for diseases based on the evolutionary process. This new discipline, in short, can undoubtedly help physicians in their medical practice, though further research is necessary to improve understanding of the range of its clinical application.

Darwinian medicine is a new field of medical science whose most important aim is to seek evolutionary explanations for the vulnerability of humankind to diseases,[1,2] namely, to study medical problems in the light of the Theory of Evolution. In simple terms, this theory states that the variation of genetic material occurs randomly in species in every generation, through cellular DNA mutations, and that the survival or extinction of a given organism is a result of natural selection, according to its capacity to adapt and reproduce itself within its own environment. Thus, through natural selection, genes providing greater reproductive success to the organisms are "selected" and remain in the genome during subsequent generations. Conversely, genes that result in less viable offspring are gradually eliminated from the population.[1,2] However, according to Darwin, natural selection was not the only process driving evolution: variability is also increased by sexual selection, thought to account for characteristics such as the behavior, shape, and physiology of organisms before, during, and after mating. Through this process, while competing with a member of the same sex and species, an individual gains reproductive advantages over a member of the opposite sex.[3]

One of the greatest mysteries of medicine is the presence, in an excellently structured machine such as the human body, of apparent failures and palliative mechanisms that cause most diseases.[4] The evolutionary approach offered by Darwinian Medicine sums up this "mystery" in two issues: why did the natural selection process not uniformly eliminate the genes that render us susceptible to diseases, and why did it not select all genes that improve our capacity to resist damages and perform "repairs"?[3]

To solve this paradox, it is necessary to make a careful distinction between the "immediate" explanations and the "evolutionary" explanations of diseases. The immediate explanations approach the pathogenic mechanisms of diseases and the body's responses to it. Evolutionary explanations, on the other hand, go back in time trying to show why human beings remain susceptible to some diseases and not to others.[1,2] However, the evolutionary and immediate explanations are not alternative ones; ie, both are necessary for the overall understanding of the disease process.[1,2]

Evolutionists have advanced several explanations for the maintenance of deleterious genes in the human genome: (1) many diseases appear mostly after the peak reproduction periods; (2) anomalous traits tend only to reduce, not eliminate, the number of progeny; (3) recessive traits may be hard for natural selection to eliminate if they only partially compromise adaptation; and (4) even if it is maladaptive to have the entire set of genes that produce a given illness, having some of them may be advantageous in certain environments.[5]

The rationale of Darwinian Medicine begins by establishing a causal relationship between previous information on health/disease and a hypothesis concerning evolutionary adaptation. Thus, the process follows a logical sequence that attempts to answer issues such as the following: Do the features studied in the human body participate in some adaptive mechanism? If these features appear functionally undesirable, how did natural selection allow them to continue for so many generations? Could they have been adaptive features in ancient periods of human development and currently cause disease?[1,3] One of the basic principles of Darwinian Medicine states that the regulation of some defense mechanisms of the human organism (ie, anxiety, fever, and cough) were shaped by natural selection for maximal reproductive success. This means that these defense mechanisms will arouse a response whenever its cost is less than the likelihood of harm multiplied by the protection. Thus, if the cost is low, defense will be expressed in a way that seems too frequent and too intense, although the system is functioning normally or near optimum. This has been called the "smoke detector principle," because of the frequent but normal and necessary false alarms from those systems.[1,2,4]

Undoubtedly, the Darwinian Medicine theory is eminently testable,[5] despite the fact that it concerns themes belonging to a time distinct from ours. We have to remember that evolutionary biology is a historical science, as opposed to chemistry and physics. Instead of using laws and experiments, researchers construct a historical narrative, ie, an attempt to reconstruct the particular scenario that led to the events and processes they are trying to explain.[6] Moreover, these field investigators have been using several skills to solve this challenge, such as the observation of physiologic and behavioral similarities between modern human beings and the higher primates (whose genomes are homologous at about 98%) and the study of human communities, which today still live as our forefathers did.[7]

Evolutionary principles have been widely applied to several fields of medical knowledge. For this reason, we are obliged to choose basic topics of this new discipline to achieve a synthesis of its main concepts.

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