Pharyngula

Medicine needs evolution

This week’s issue of Science contains a very strongly worded statement about the utility of evolutionary biology in medicine, and calls for an increase in education about evolution at all levels of the medical curriculum, from high school to med school. I’ve put the whole thing below the fold—it’s good reading.

Medicine Needs Evolution

The citation of “Evolution in Action” as Science‘s 2005 breakthrough of the year confirms that evolution is the vibrant foundation for all biology. Its contributions to understanding
infectious disease and genetics are widely recognized, but its full potential for use in medicine has yet
to be realized. Some insights have immediate clinical applications, but most are fundamental, as is the
case in other basic sciences. Simply put, training in evolutionary thinking can help both biomedical
researchers and clinicians ask useful questions that they might not otherwise pose.

Although anatomy, physiology, biochemistry, and embryology are recognized as basic sciences
for medicine, evolutionary biology is not. Future clinicians are generally not taught evolutionary
explanations for why our bodies are vulnerable to certain kinds of failure. The narrowness
of the birth canal, the existence of wisdom teeth, and the persistence of genes that cause
bipolar disease and senescence all have their origins in our evolutionary history. In a whole
array of clinical and basic science challenges, evolutionary biology is turning out to be
crucial. For example, the evolution of antibiotic resistance is widely recognized, but few
appreciate how competition among bacteria has shaped chemical weapons and resistance
factors in an arms race that has been going on for hundreds of millions of years. The
incorrect idea that selection reliably shapes a happy coexistence of hosts and pathogens
persists, despite evidence for the evolution of increased virulence when disease transmission
occurs through vectors such as insects, needles, or clinicians’hands. There is growing
recognition that cough, fever, and diarrhea are useful responses shaped by natural selection,
but knowing when is it safe to block them will require studies grounded in an understanding
of how selection shaped the systems that regulate such defenses and the compromises
that had to be struck.

Evolution is also the origin of apparent anatomical anomalies such as the vulnerabilities
of the lower back. Biochemistry courses cover bilirubin metabolism, but an evolutionary
explanation for why bilirubin is synthesized at all is new: It is an efficient free-radical
scavenger. Pharmacology emphasizes individual variation in genes encoding cytochrome
P450s, but their evolutionary origins in processing dietary toxins are just being fully appreciated. In
physiology, fetal nutritional stress appears to flip an evolved switch that sets the body into a state that
protects against starvation. When these individuals encounter modern diets, they respond with the
deadly metabolic syndrome of obesity, hypertension, and diabetes.

The triumphs of molecular biology call attention to evolutionary factors responsible for certain
genetic diseases. The textbook example is sickle-cell disease, whose carriers are resistant to malaria.
Similar protection against infection has been hypothesized for other disorders. Which aspects of the
modern environment are pathogenic? We need to find out. Increases in breast cancer have been
attributed to hormone exposure in modern women who have four times as many menstrual cycles as
women in cultures without birth control. Other studies suggest that nighttime exposure to light increases
the risk of breast cancer by inhibiting the normal nighttime surge of melatonin, which may decrease
tumor growth. Evolution has also provided some explanations for conditions such as infertility. The
process that eliminates 99.99% of oocytes may have evolved to protect against common genetic defects.
And some recurrent spontaneous miscarriages may arise from a system evolved to protect against
investing in offspring with combinations of specific genes that predispose to early death from infection.

These and other examples make a strong case for recognizing evolution as a basic science for
medicine. What actions would bring the full power of evolutionary biology to bear on human disease?
We suggest three. First, include questions about evolution in medical licensing examinations; this will
motivate curriculum committees to incorporate relevant basic science education. Second, ensure
evolutionary expertise in agencies that fund biomedical research. Third, incorporate evolution into every
relevant high school, undergraduate, and graduate course. These three changes will help clinicians and
biomedical researchers understand that both the human body and its pathogens are not perfectly
designed machines but evolving biological systems shaped by selection under the constraints of
tradeoffs that produce specific compromises and vulnerabilities. Powerful insights from evolutionary
biology generate new questions whose answers will help improve human health.

Randolph M. Nesse, Stephen C. Stearns, Gilbert S. Omenn

Comments

  1. #1 LadyGrey
    February 23, 2006

    Well put. An acquaintance once mentioned a friend in medical school who was a creationist. I was horrified, and said strongly that I would never want him as a doctor. I do not trust someone who doesn’t understand/believe in evolution to practice medicine, and it had never occured to me that someone so anti-science and anti-intellectual would actually pursue medicine, but apparently it can happen.

  2. #2 Grumpy
    February 23, 2006

    This may be an urban legend (read: erroneous factoid), but…

    I had heard that the surgeon who implanted a baboon heart in Baby Faye in 1984 was a creationist. This is significant if, say, a chimp heart would’ve been more suitable but the surgeon didn’t think it made any difference.

  3. #3 Kristine
    February 24, 2006

    Great essay, but I caught that “evolved to protect” phrase, too. Ever since this ID conspiracy I have become more sensitive to alegoric and potentially confusing phrases such as “designed to,” “intended for,” etc. Of course I know what the author is really saying, but it really points to how religion, since it arose before science, dictates our thoughts and speech.

  4. #4 Jonathan Badger
    February 24, 2006

    Speaking of this weeks’ Science, did anyone read the article “Evangelicals, Scientists Reach Common Ground on Climate Change”? While it’s good that otherwise conservative christians are begining to doubt the Republican line on the environment, there are some scary lines in it like:

    Those two gatherings helped establish crucial trust, Ball says. But more work was needed before the 86 leaders were ready to sign a statement last year that “human-induced climate change is real.” Rightward political leanings–”Evangelists aren’t tree-huggers,” one Christian biologist says–were one obstacle. So too was what DeWitt calls science’s “connection with evolution.”

    “Connection with evolution”? As if it were outside science.

  5. #5 mark
    February 24, 2006

    You don’t need to understand evolution to reap the benefits of homeopothy or coffee enemas.