Evolutionary Medicine

Evolutionary medicine, sometimes referred to as Darwinian medicine, is an emerging academic field that employs evolutionary principles to aid in the understanding of human health and disease at the levels of both the individual and the population. While its main value lies in giving an ultimate (evolutionary) perspective to patterns of health and disease, there are areas of clinical medicine and public health where it has direct application. Whereas the bulk of clinical medicine is focused on issues of proximate causation and, in particular, pathophysiological mechanisms and their treatment, evolutionary perspectives focus on understanding how and why traits evolved and how they confer greater or lesser disease risk. Evolutionary perspectives also give weight to ecological dimensions, particularly the positioning of individuals within their social and environmental context, and also their relationship to other organisms, including gut microbiota, parasites, and infectious agents. A core principle of evolutionary medicine is that selection has operated to optimize reproductive fitness, and that this is not the same as selection for health or longevity. Indeed, selection pressures wane with age, and humans have had increasing median lifespans in recent centuries, leading to greater incidence of diseases that occur in the post-reproductive period. Another distinctive feature is an appreciation of the role of cultural evolution and technology in changing the environments within which humans now live—changes that can exaggerate the mismatch between evolved biology and the environment, with health consequences. Selection can occur not only at the level of the whole organism but also at the level of a cellular clone, and evolutionary concepts have become important in understanding the progression of cancer. More controversially, evolutionary concepts are contributing to understanding the origin of human behavior at both an individual and a group level, and also to understanding some psychiatric symptomatology. Evolutionary history also contributes to disease risk through anatomical and biochemical vestiges such as the appendix or the lack of the gene to synthesize ascorbic acid (and prevent scurvy); through genetic mechanisms such as founder effects and balancing selection; and through the evolution of defense mechanisms that may operate excessively (e.g., autoimmune disorders), which can explain much common symptomatology (e.g., fever). Being well versed in evolutionary concepts enables medical students and clinicians to integrate factual knowledge of cellular biology, physiology, and anatomy into a meaningful framework, thus promoting a better understanding of human health and disease. This sentiment is being embraced by a growing number of medical schools worldwide as evidenced by the inclusion of evolutionary medicine into the core curricula.