A recent series of article in the Proceedings of the National Academy of Sciences (PNAS) discusses the role of evolutionary biology in modern medicine. The authors collectively make a forceful point – medicine is an applied science. It is based upon a number of basic sciences, and one of those basic sciences is evolution.
The most obvious example is bacterial antibiotic resistance. Antibiotics place a selective pressure on a bacterial population, often resulting in the emergence of resistant strains. Understanding this “evolutionary arms race” between bacteria and antibiotics allows us to develop strategies for minimizing resistance.
But there are less obvious ways in which evolutionary principles apply to infectious diseases. It has been known for a long time that sickle-cell trait provides resistance to malaria (the blood cells are less hospitable to the P. falciparum protozoan parasite that is one cause of malaria). This explains the persistence of sickle cell disease in populations where malaria is endemic.
Evolutionary principles may also improve our vaccine strategy. Vaccines are another way to create selective pressures on infectious organisms. We may inadvertently target vaccines against proteins that select out less virulent strains, selecting for the more virulent or infectious strains. Understanding of this allows us to instead target vaccines against virulence without targeting less deadly strains.
An example given is the following:
The diphtheria toxoid vaccine selects against toxin production, which is what causes disease, rather than other features of Corynebacterium. Thus, diphtheria infections and clinical isolations still occur, but the extant strains lack toxin production.
The authors also provide examples of how evolutionary principles can direct future research. They reference new research looking into the role of intestinal parasites and autoimmune diseases. The research is based upon the premise that humans co-evolved not only with our intestinal flora, but with certain parasites, such as intestinal worms. Now we live in a largely hygienic environment, and have even taken steps to eliminate parasites. This may have unintentionally deprived our immune systems of needed stimulation, resulting in poor immune regulation, and subsequent increase in auto-immune diseases like asthma and multiple sclerosis.
The authors also point out that the incidence of lactose intolerance inversely correlates with the duration of dairy farming in various populations. Populations that have consumed dairy products for thousands of years have evolved the ability to produce lactase even into adulthood, while populations without dairy farming have not.
Knowledge of common descent and cladistic patterns (evolutionary relationships) also allows for the targeting of drugs at genes and gene products that are present in certain pests and parasites but not in the crops or animals they infect.
There are more examples, and collective they provide a compelling case that evolutionary principles are important to understanding populations, genetics, infectious diseasease, diet, and other issues of public health – in diagnosis, treatment, and research. Therefore, the authors argue, evolution is an important topic for medical professionals to understand, and I completely agree.
In the press release for this special issue of PNAS, they report:
Their ideas may be gaining ground. This past summer, the American Association of Medical Colleges (AAMC) and the Howard Hughes Medical Institute (HHMI) published a joint report, titled Scientific Foundations for Future Physicians. The report calls for ambitious changes in the science content in the premedical curriculum and on the Medical College Admission Test (MCAT), including increased emphasis on evolution. “For the first time, the AAMC and HHMI are recommending that evolution be one of the basic sciences students learn before they come to medical school,” Nesse explained.
(Randolph Nesse is an author on the final paper in the series.)
Increasing the basic science standards for medical students can only help the goals of science-based medicine, and I am glad to see that evolutionary biology is being recognized as the core basic science that it is.
This recognition is also not new. There is already a journal of evolution in medicine, available online as the Evolution and Medicine Review. Some of the current PNAS authors have also written about the topic previously, including this 2006 editorial in Science titled Medicine Needs Evolution.
The PNAS series is an indicator that their views are indeed taken seriously.