Overlooking the Foundation of your Foundation: Darwinian Medicine's Role in the Medical Community
In “Darwin’s Dangerous Ideas,” Daniel Dennett equates the theory of evolution with a universal acid that cannot be contained and “eats through virtually every traditional concept” (Dennett 1995). As a premedical student aspiring to become a future physician, I was eager to discover the erosive effects of this universal acid on the medical field. While Charles Darwin dropped out of medical school, it appears that some of his key evolutionary concepts are seeking enrollment in order to substantiate the field of Darwinian medicine which involves looking at the practice of medicine through an evolution lens. Several physicians and directors of medical schools who fail to see the relevance of evolution to medicine and express concern about the time constraints of the current medical curriculum, have invested a great deal of effort into preventing the spreading of this universal acid into their field. As of 2006, only eight out of the 126 medical schools in the United States offered a course that referenced evolution (Baker 2006). This paper attempts to encourage medical schools to incorporate Darwinian medicine into their pre-clinical curriculums by discussing the insights into disease and the human body provided by this evolutionary approach to medicine.
Investigations on the applications of evolution to medicine first emerged in the 1880’s and continued on until the 1940’s when evolutionary medicine’s association with eugenics in Nazi Germany led to the field’s disappearance (Zampieri 2009). Evolutionary medicine resurfaced in the early 1990’s with the publication of work that resulted from the collaboration of physician Randolph Nesse and evolutionary theorist George Williams, two notable proponents and founding fathers of modern Darwinian medicine (Zampieri 2009). Despite their common goal of utilizing evolutionary theory to better understand medicine, contemporary Darwinian medicine differs substantially from its predecessor. The initial form of evolutionary medicine believed that disease came about from traits that evaded natural selection whereas its current embodiment views disease as arising from flaws maintained by natural selection (Zampieri 2009). Additionally, the earlier version of evolutionary medicine revolved around illness in relationship to an individual while modern Darwinian medicine focuses on the population level (Zampieri 2009). Traditional western medicine also tends to center around sickness in the individual (Nesse 2001a). Current western medicine takes a mechanistic approach to health as it seeks to answer proximate questions about how the body works and how it responds to disease and considers sickness to be a defect in the machine that is the body (Nesse 2001a). Darwinian medicine on the other hand, asks more ultimate questions such as what is the origin of a disease and why are we vulnerable to certain diseases (Nesse 2001a). In doing so, Darwinian medicine liberates the body from this machine analogy as it views the flaws that give rise to disease as having some sort of evolutionary advantage (Nesse 2001a).
One such reason that we experience disease deals with the fact that pathogens reproduce and evolve at a faster rate than our methods for combating them (Nesse 2001b). This is exemplified by one of the more popularly recognized applications of evolution to medicine: antibiotic resistance. Improper and excessive use of antibiotics leads to the selection of strains of bacteria that have acquired a genetic mutation that confers resistance to the misused antibiotic. This selected strain of bacteria reproduces, passes this resistance mutation to their offspring, and eventually renders the specific antibiotic ineffective. This revelation about the evolution of antibiotic resistance has significantly influenced the practice of dispensing antibiotics and drug design research. The fast paced nature of pathogen evolution also sharpens physicians’ understanding of virulence. Several scientists, including physicians, still falsely assume that as evolution proceeds, natural selection will favor the more benign pathogens since the lethal pathogens possess a major disadvantage in that they kill their host which serves as their life support system. However, natural selection selects for genetic variations that enhance the microbe’s reproductive success which depends on its ability to spread its offspring to other hosts so to ensure that the host doesn’t become overpopulated and die (Nesse 2001b). While it would be unfavorable for pathogens to be lethal if their method of transmission requires their hosts to move around and interact with individuals, pathogens that rely on vectors for transmission do not have this problem and thus do not experience a selection pressure for less virulence (Nesse 2001b). This plays a role in the medical field since certain pathogens such as E-coli, spread from patient to patient in a hospital via the hands of medical staff which serve as vectors for the disease (Nesse 2001b). Awareness of the selection pressures on pathogen virulence has important consequences for doctor-patient interaction and research aimed at eradicating vector-born diseases.
Although our body and pharmaceutical companies struggle to keep up with the rapidly evolving pathogens, natural selection has equipped us with several defense mechanisms against these microbes. Despite the unpleasantness they evoke, a fever, coughing, and diarrhea can prove advantageous since they act as mechanisms employed by the body to expel pathogens and to create an inhospitable environment for them while alerting one to the possible microbe invasion occurring within their body (Nesse 2001a). Consequently, in certain cases, suppressing these symptoms with medication may actually do more harm than good. A 2000 study investigating why pregnant women experience morning sickness found that women who suffered from morning sickness were less likely to spontaneously miscarry than pregnant women unaffected by morning sickness (Flaxman and Sherman 2000). From these results, the study concluded that morning sickness protected the vulnerable fetus by forcing women to vomit food items that typically contain risky toxins and warned expectant mothers about the potential hazards that could arise from blocking this defense strategy with anti-nausea medication (Flaxman and Sherman 2000). Acknowledging the beneficial role that certain symptoms play in warding off disease presents physicians with a new set of useful questions to consider when treating patients. Doctors must now decipher whether the patient’s symptom is a defense mechanism or a tool used by the pathogen and determine the necessity and possible negative outcomes of treating the symptom (Flaxman and Sherman 2000).
The pain one suffers in return for the protection provided by a symptom such as a fever represents one of the many trade offs that the evolution of the body revolves around. These trade offs help explain why we are vulnerable to disease. Contrary to popular belief, natural selection does not select for health but rather for reproductive fitness (Nesse 2001a). This means that natural selection will favor a genetic variation that increases reproductive fitness even if that same gene causes cancer later on in life (Nesse 2001a). Physicians stand to benefit from such an understanding of the reasoning behind a population’s susceptibility to disease since their profession requires an extensive knowledge on disease and the human body.
Another explanation for why we fall ill stems from the idea that the human body is still not fully adapted to the modern environment (Nesse 2001a). In an attempt to gain insight into why it plagues a large portion of the human race, researchers applied this evolutionary explanation to obesity. It seems that our bodies still retain some behaviors suited to the ancient environment where our earliest predecessors lived as the shadow following the modern day patient in the above picture (from Baker 2006) illustrates. In this ancient environment, the human body exerted an immense amount of energy seeking food and needed to be prepared for periods of food shortage (Nesse 2001a). For this reason, our body yearned for high caloric, fatty foods that were scarce in the ancient world and did not waste energy on extraneous activities such as recreational exercise (Nesse 2001b). Possession of this innate craving for high caloric foods and a desire to avoid exercise in the modern world where a plethora of fatty foods are easily accessible has led to the obesity crisis (Nesse 2001b). This explanatory insight can help direct doctors’ treatment plans for obesity and other diseases that emerge from environmental maladaptations.
One of the biggest benefits doctors-in-training can derive from Darwinian Medicine is its ability to unite all of the wide ranging information taught in medical school in the same way that Daniel Dennett believes “evolution by natural selection unifies the realm of life” (Nesse 2001b and Dennett 1995). Reflecting on the unifying nature of Darwinian medicine reminded me of our “Stories of Evolution” class discussion in which we classified almost everything as a story. Since Darwinian medicine ties everything in medicine together, I am not sure whether it acts as the whole story of medicine, a mere piece of the story that allows us to see the whole picture, or an entirely different story on medicine. Regardless of its story classification, Darwinian medicine does not contradict our current story of western medicine but rather, enhances it and has the potential to produce more effective physicians. For that reason, I invite medical school directors to assess the story of medicine that they aim to equip their students with and consider incorporating Darwinian medicine into it.