Some scientists call for a bigger dose of evolution in doctors’ educations
By MITZI BAKER
Joon Yun, MD, began considering how evolution applies to human health a decade ago, when his first heart disease patients died. These cases disturbed Yun, then a Stanford radiology resident. But they also intrigued him.
Having studied evolutionary biology in college, Yun tried fitting these medical failures into that framework.
His mind wandered to the early days of humans when heart disease was a rare trigger of death. In the prehistoric era, a more likely cause of death would have been an attack by a predator. The human body’s response to trauma handles this type of assault by immediately springing to action: The blood forms clots and the blood vessels tighten, together slowing blood loss, and inflammation kicks in to combat infection. The genes governing these responses to trauma presumably were favored during evolution and have become the “factory setting” in modern humans.
Returning his attention to the modern times, Yun observed that predation as a trigger of the trauma response had virtually disappeared in modern humans. Furthermore, distinctly modern conditions such as smoking and high blood pressure inadvertently trigger the trauma response, which, by activating inflammation, clotting and vessel narrowing, create what we now interpret as atherosclerosis. Distressingly, Yun saw that many current treatments for heart disease, such as propping open clogged arteries through angioplasty or stenting, trigger this ancient trauma response. Vessels irritated by the intrusions simply choke up again.
The idea dawned: Perhaps a little respect for human evolution was in order. Though Yun didn’t realize it at the time, he wasn’t alone in his conviction. A few dozen physicians and medical researchers at institutions throughout the world had begun in the 1990s to pursue this same line of thought. Now they’re angling to get evolutionary medicine taught in medical schools. Whether they’ll succeed is anyone’s guess.
The origin of the thesis
The push to get darwin into medical school began when University of Michigan psychiatrist Randolph Nesse, MD, teamed with George Williams, PhD, an evolutionary biologist at the State University of New York-Stony Brook. Their 1991 paper in the Quarterly Review of Biology laid the groundwork for applying evolutionary theory to medical issues, coining the term “Darwinian medicine.” They published the first book on the topic in 1996 — Why We Get Sick: The New Science of Darwinian Medicine. Nesse worked on the book while spending a sabbatical year at Stanford. He credits the personal generosity of Brant Wenegrat, MD, associate professor of psychiatry and behavioral sciences, emeritus — who Nesse says is one of the world’s best scholars in the area of evolution and psychiatry — for making his book possible.
Why is it a problem that evolutionary medicine isn’t taught in medical schools? Because doctors end up with false beliefs about disease, according to University of Michigan psychiatrist Randolph Nesse, MD, considered to be the founder of Darwinian medicine.
“Some of these thoughts are 20 years behind the times in evolutionary thinking,” he says. “If someone were 20 years behind the times in understanding genes, we would just throw our hands up, but for some reason we don’t do it for evolutionary medicine.”
Myth: Bacteria and viruses become less virulent the longer the interaction with the host species has been going on.
Evolutionary insight: Natural selection would seem to favor lower virulence, as the host must remain mobile enough to interact with others to spread the infecting organism.
But when transmission occurs through insects, needles or clinicians’ hands, virulence increases — there is no longer a need for a functional host. In hospitals, health-care workers’ hands can actually select for more virulent strains.
Myth: Aging happens because parts wear out.
Evolutionary insight: Rather than a degenerative disease, aging could be viewed as a genetic trade-off. Genes that offer advantages in youth might cause the problems seen with aging and eventually death. For example, strong immune defenses protect against infection but these same responses also inflict continual, low-level tissue damage.
Myth: Annoying responses to infection — such as fever, anemia and diarrhea — are unnecessary and should be alleviated with drugs.
Evolutionary insight:Defenses are often confused with disease states. Fever and low iron levels have evolved to combat invading bacteria, while vomiting and diarrhea help flush the body of infection and toxins. While each of these defenses can cause problems in the extreme, blindly blocking them could be deadly.
An editorial in Science this February, “Medicine needs evolution,” sets out a call to action. The three authors — Nesse; Stephen Stearns, PhD, an evolutionary biologist from Yale; and Gil Omenn, MD, PhD, a geneticist and current president of the American Association for the Advancement of Science — argue for including questions about evolution in medical licensing exams, ensuring evolutionary expertise in agencies funding biomedical research and incorporating evolution into every relevant class from high school on. They contend that while evolution’s role in understanding infectious disease and genetics is widely recognized, its potential for use in medicine is barely acknowledged.
The field’s advocates argue that an evolutionary context will prod researchers and clinicians to ask better questions. “Once you get doctors asking ‘Why is a body vulnerable to this disease?’ and ‘Why didn’t natural selection make the body less vulnerable?’ a lightbulb just goes on, and they recognize that there is a whole other set of questions that needs to be asked about every single disease,” says Nesse. Every topic in medicine can become an evolutionary puzzle — by asking questions such as why the appendix is still there (not just how to take it out), why the genes for Alzheimer’s disease don’t get selected out and why rates of cardiovascular disease have skyrocketed in recent years.
So, where can students take a course in evolution and medicine? In dozens of undergraduate programs across the country, and scores more worldwide, but not in any U.S. medical school, says Nesse. A query of an American Association of Medical Colleges database that contains detailed information about the course offerings of the majority of U.S. medical schools turned up only eight medical schools with any courses mentioning “evolution.” That’s out of 126 medical schools in the country.
Nesse, Stearns and others have been trying to convince medical school deans to incorporate evolutionary ideas into their curricula, but so far, little luck. They know that deans feel beleaguered by demands to add new subjects to the already crowded schedule — nutrition, alcoholism and aging to name a few. “But still, it’s preposterous that evolution is not a part of medical education,” says Nesse. “Evolution offers a broad framework on which you can organize and understand all kinds of facts and principles. It ties together medical education instead of leaving it hanging as 50,000 discrete facts.”
Stanford medical school’s curriculum director believes students learn about evolution’s role in medicine despite the absence of a course on the topic. “It is impossible to be a good physician without understanding the evolutionary process,” says Julie Parsonnet, MD, senior associate dean for medical education. She notes the importance of evolutionary explanations for antimicrobial resistance and the emergence of new infectious diseases, as well as more complex chronic diseases, such as the cardiovascular problems that piqued Yun’s interest years ago. “We do teach these examples in various classes. And we need to be sure that students have the basic knowledge to integrate them into their thinking. A full course in Darwinian medicine, however, probably exceeds these current needs.”
Medical schools might not be ready for full-blown evolutionary theory courses — at least not in the United States. Evolutionary medicine proponent Stephen Lewis, PhD, a biology lecturer at the University of Chester in England, says: “The impression that we get in England is that your education system is experiencing very strong anti-evolutionary feeling coming from certain religious groups.”
Lewis agrees with Parsonnet that specific evolutionary medicine courses probably aren’t necessary, but that the basic biological principles on which medicine is based should be infused with evolutionary concepts. “If, as Theodosius Dobzhansky stated, ‘Nothing in biology makes sense except in the light of evolution,’ then all biology teaching must be done in the light of evolution to make it make sense,” he says. “Otherwise biology loses all its explanatory power and becomes little more than stamp collecting.”
Influencing medicine: Another route evolution can take
Perhaps part of the problem in convincing medical practitioners to embrace evolution is the nature of the science. Evolutionary hypotheses about human physiology are notoriously hard to investigate, given humans’ long generation times.
Add to this the fact that the field has failed so far to provide clinically useful findings and you see why medical schools lack interest, says Lewis. “There is much about explanation and understanding but little about treating and curing,” he says.
Even if medical institutions aren’t concerned about evolution’s lessons, at least one investment firm is. These days Yun, now a Stanford staff physician, and Stanford radiology resident Patrick Lee, MD, are partners at Palo Alto Investors, where evolutionary insights guide their health-care investment recommendations. Of the billion dollars under management, the firm has invested $350 million in health care, much of that in companies that produce devices that make sense from an evolutionary standpoint. In other words, stents are out; gentler procedures that don’t escalate the trauma response are in. Drug-delivery systems for treating kidney disease intravenously are out; delivering the drugs directly to the kidneys to bypass the trauma response is in.
The idea is that treatments shouldn’t cause further stress to the body. “Thus, we can unwind Darwinian maladaptations,” says Yun. If a product makes sense from the evolutionary perspective, reducing the trauma response rather than exacerbating it, he and like-minded physicians are interested.
Originally published on the Stanford Medicine Magazine in Summer 2006.