As a student in the highly interdisciplinary Hominid Paleobiology Doctoral Program, with an even broader interdisciplinary focus on evolutionary neuroscience, I’ve had the opportunity to learn from instructors hailing from a wide variety of fields. I am currently enjoying a course on neurodevelopmental disorders as taught by a rotating list of neuroscience researchers, medical researchers, and clinical doctors. Like a dog that hears the word “food”, I immediately snap to attention any time the word “evolution” is mentioned in class. However, my trigger word is usually embedded within a sentence along the lines of “…And this weird biological quirk probably has something to do with evolution, but who knows.” Not to the discredit of my fantastic instructors, these moments strike me as missed opportunities to investigate the underlying reasons behind these biological quirks, especially in the context of human medicine. In the midst of my search for related literature, I stumbled across a whole discipline that I admittedly didn’t even realize existed, known as evolutionary medicine.
Evolutionary medicine is the application of evolutionary theory to human health[1]. For if medicine is founded in biology, and biology is founded in evolution, why should medicine not also be founded in evolution?2,3 It has been applied to topics as diverse as sickle cell anemia, susceptibility to viral and bacterial infections, depression, anxiety, drug abuse, obesity, cancer, etc[1]. And yet evolution is incorporated into less than 4% of medical school curricula, and is indeed largely absent from thinking within the medical profession[1]. Charles Darwin’s ‘The Origin of Species’ was published over 150 years ago and has since completely revolutionized biology and all its related disciplines. So what’s the hold up when it comes to medicine?
Proponents of incorporating evolutionary medicine as a fundamental part of medical school education have been shot down for a number of reasons. Aside from the already overly saturated course load in most medical schools, critics argue that the answers to why things go wrong in patients has nothing to offer that can’t be supplied by the answers to how things go wrong[1,2,3]. In other words, they only want to know how a person comes to contract pneumonia and how to effectively treat it, not why our bodies evolved in such a way that leaves us susceptible to pneumonia in the first place. Furthermore, they argue that stories about what evolutionary pressures molded our hominin ancestors into our modern state are far too speculative and not empirically testable enough for clinical standards.3 Unfortunately, some blindly “adaptationist” claims have tainted the reputation of evolutionary medicine (and the related field of evolutionary psychology) by overstating the concept that everything in the human body is simply just another adaptation in disguise[3].
Despite this skepticism, evolution has far more to offer medicine than is currently recognized. There is vast insight to be gained from understanding the human body (including the brain) not as a perfectly designed machine at the apex of all life, but rather the cumulative product of several billion years of evolution that is both remarkable and inherently flawed. Evolution offers a unified framework in which to place the overwhelming wealth of seemingly unrelated facts that medical students must learn[2]. Perhaps even more importantly, this framework enables us to make predictions about which biological mechanisms (e.g. genes, biochemical pathways) evolution most likely altered in order to achieve a certain function, and which ones weren’t an option (e.g. constraints due to the pleiotropic effects of a particular gene in other parts of the body, or constraints of embryonic development).1 Lastly, it can tell us why mismatches between the environments of our ancestors and our current environment gives rise to “diseases of civilization” (e.g. sedentary lifestyle giving rise to morbid obesity)[1,2]. I don’t mean to suggest that what is “natural” for our species is necessarily always the best thing for us now. Cultural innovations have of course greatly extended our average lifespan and our quality of life. Rather, with an appropriately cautious and thorough approach that’s befitting to any field that concerns the safety and well-being of human life, evolutionary medicine has the potential to fuel medical insights and eventually paint a truly holistic picture of human biology and health.
Imagine you have a toy musical box with complicated internal parts that work together to play music. Then, in a stroke of bad luck you accidentally drop it, instantly breaking open the box and discombobulating the gears inside. You might be able to figure out how to put it back together based on your memory of what it looked like before. Alternatively, if you acquire the notes of the engineer who designed the box, you could discover why the parts were put together the way they were and thus gain a more complete picture of how they work in synchrony to ultimately produce music. Perhaps you could even use this new knowledge to figure out how to add features to that box to prevent it from breaking in the future, should you have the misfortune of dropping it a second time.
To paraphrase Theodosius Dobzhansky, nothing in biology makes sense except in light of evolution, and by extension, nothing in medicine makes sense except in light of evolution[3].
References:
1 Naugler, C. (2008). Evolutionary Medicine: Update on the Relevance to Family Practice. Canadian Family Physician, 54: 1265-9.
2 Nesse, R. (2009). Making Evolutionary Biology a Basic Science for Medicine. PNAS, Early Edition: 1-8.
3 Cournoyea, M. (2013). Ancestral Assumptions and the Clinical Uncertainty of Evolutionary Medicine. Perspectives in Biology and Medicine, 56: 1: 36-52.