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Evolution in Medicine

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.

Conclusion

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.

Posted in: Evolution, Science and Medicine

Leave a Comment (21) ↓

21 thoughts on “Evolution in Medicine

  1. Zoe237 says:

    Fascinating stuff. I was just reading the PNAS proceedings last night in relationship to the placebo thread (causes of chronic disease), but didn’t realize it was a series. Thanks!

    Evolution of the human lifespan and diseases of aging: Roles of infection, inflammation, and nutrition
    Caleb E. Finch1
    + Author Affiliations

    http://www.pnas.org/content/107/suppl.1/1718.full

  2. micheleinmichigan says:

    I love this stuff!

    Hmm, I wonder if controlled intestinal parasite infection to prevent auto-immune disease would be an even tougher sell than maggot debridement therapy.

  3. I wish someone would evolve a Rhinovirus that wasn’t so darned annoying!

  4. KathyO says:

    Eugenie Scott of the National Center for Science Education talks about how biology teachers at every level should find ways to incorporate evolution into every lesson. After all, evolution does impact every aspect of biology, apparently even medicine.

  5. Alaskan says:

    This is a welcomed article, thank you. It’s nice to see Uncle George C. William’s novel work, started decades ago beginning to blossom as evidenced in this important paper by one of his colleagues, R.M. Nesse.

  6. Watcher says:

    This was always something I try to stress to students when I talk about antibiotic resistance. It’s just not possible to separate the two.

    The opposite is true too. Antibiotic resistance is a great example of evolution by natural selection occurring before our very (microscope-aided) eyes.

  7. Draal says:

    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.

    I seem to recall Bill Maher and George Carlin both making similar statements, that it’s better to keep an immune system challenged versus being too obsessive about vaccinations or hygiene, respectively. meh.

  8. Draal says:

    “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.”
    I seem to recall Bill Maher and George Carlin both making similar statements, that it’s better to keep an immune system challenged versus being too obsessive about vaccinations or hygiene, respectively. meh.

  9. Fifi says:

    Thanks for a great post Dr Novella, this is a fascinating subject.

  10. Heinleiner says:

    Dr. Novella, one minor correction:

    “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 bacteria that is one cause of malaria).”

    P. falciparum is a type of protozoan, not a bacterium.

    I had a guest in my Biology of Infectious Diseases class come in and talk about why Malaria is just so damned hard to create a vaccine for, and one of the reasons (among others) is because P. falciparum (et. al.) aren’t “simple” bacteria. All that damned sexual + asexual reproduction. And to think one of the theories for the emergence of sexual reproduction was to combat parasites :D.

    Oh, and this is my first post. Love the Blogs + SGU!

  11. BillyJoe says:

    Draal,

    “I seem to recall Bill Maher…making similar statements, that it’s better to keep an immune system challenged versus being too obsessive about vaccinations…”

    I suppose you told him that vaccinations, like the microorganisms they protect against, also challenge the immune system but with enormously less risk of harming or destroying the body. ;)

  12. Heinleiner – thanks for pointing that out. I corrected the post.

  13. Zetetic says:

    I recently had a very heated discussion with a raw milk advocate who maintained that the human species has enjoyed cow’s milk as a dietary staple “since the beginning of time” and it was the most natural of foods for humans. If he’s a new earth creationist (I don’t know), maybe his timeframe is correct. I can use the evolution of lactose intolerance as ammunition!

  14. Danio says:

    Zetetic, it’s actually the evolution of lactose tolerance that’s evolved. In the ancestral state, the lactase gene switches off after the developmental time during which young mammals drink mother’s milk. When mutations resulting in the failure to downregulate enzyme production occurred in dairy-farming populations, a survival advantage was conferred to the members of these groups.

    http://www.sciencedaily.com/releases/2005/06/050602012109.htm

  15. Taylor says:

    Great blog and great points….except for one issue which I see is constantly mischaracterized, IMHO.

    The actual mechanism of antibiotic resistance is usually mediated by a mutation which makes the pathogen LESS fit. It usually involves a partial destruction of a trait, rather than formation of a new and improved one.

    Consider sulfadoxine which inhibits the enzyme DHPS. A mutation in the enzyme makes the enzyme less efficient, but is selected for in an antibiotic environment because that mutation is thought to change the conformation of the enzyme. The new conformation no longer binds to the antibiotic, rendering the antibiotic ineffective.

    The evidence demonstrating this is straight forward. When the antibiotic is no longer present, the more efficient version of the enzyme returns in full force. The less fit mutant strain dies out. This is why community acquired infections are usually much easier to treat (because they have less antibiotic resistance) than hospital acquired ones. (Obviously, MRSA would be one example of an important exception.)

    So it is usually not an “arms race” that is observed when you look at antibiotic resistance in real time. Instead it is more like a “scorched earth strategy”: the defender escapes because of the destruction of its own internal machinery, a phenomenon mediated mutation and selection.

  16. Taylor says:

    “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 difference, of course, is that the first statement is an emerging hypothesis based on empirical evidence and a firm understanding of Immunology. Still, more work needs to be done to validate it and to come up with a useful, scientifically proven intervention, if that is even possible.

    On the other hand, Maher’s statement is based on pure intuition which completely lacks an understanding of Biology. There is no empirical evidence for his claim.

  17. Taylor says:

    The above comment does not contain the second paragraph, which was a post from Draal.

    Here is the comment again.

    “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.”

    “I seem to recall Bill Maher and George Carlin both making similar statements, that it’s better to keep an immune system challenged versus being too obsessive about vaccinations or hygiene, respectively. meh.”

    The difference, of course, is that the first statement is an emerging hypothesis based on empirical evidence and a firm understanding of Immunology. Still, more work needs to be done to validate it and to come up with a useful, scientifically proven intervention, if that is even possible.

    On the other hand, Maher’s statement is based on pure intuition which completely lacks an understanding of Biology. There is no empirical evidence for his claim.

  18. B Hitt says:

    “Nothing in biology makes sense except in the light of evolution.” – Theodosius Dobzhansky

    Evolutionary principles are also critical in studying the molecular biology of disease. Genetic information that has been conserved throughout evolution points out protein domains with important functions, and understanding the evolutionary lineage of genes helps us use animal models to study the causes of disease and identify therapeutic targets.

    Thank you for this, Dr. Novella.

  19. BillyJoe says:

    Taylor,

    “The actual mechanism of antibiotic resistance is usually mediated by a mutation which makes the pathogen LESS fit.”

    Let me get this right: A bacteria that survives in its antibiotic drenched environment is LESS fit than one that does not survive???

  20. Sophile says:

    It’s not simply the immune systems evolution, but physical traits which have developed to protect our vital parts from damage/trauma — e.g. the phenomenon known as ‘hard-body training’, where, through repeated trauma the haversian (sp?) canals ‘fill-in’ the sponge-like bone area, which hardens, creating a better device for physical protection of one’s vital parts (especially the BioSuperComputer – aka the Brain). I only use this example because I speak from personal experience. Throughout my rowdy childhood, my skull was exposed to serious, consistent trauma, developing a VERY hard head (not just figuratively). When I was in my accident [hit-n-run, flew 100 ft., TBI/coma], I not only came out of the coma, but seemingly retained all of my mental faculties, as I returned to graduate from UCLA with College Honors.

    P.S. My final quarter had a directed research project for which I wrote my final paper entitled “Ethics THROUGH Evolution”.

    I apologize for the obliquity.

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