Saturday, June 25, 2011

Jerry Coyne and Darwinian medicine: Introduction

Jerry Coyne recently attended a meeting that included presentations on Darwinian medicine, which is the application of evolutionary biology to medical education, treatment and research.

Advocates of Darwinian medicine propose that each disease has a proximate cause and an evolutionary cause. The proximate cause is the scientific cause, traditionally understood. The proximate cause of a genetic disease would include, for example, the nature of the gene mutation, the defect in the protein product caused by the gene defect, the disease manifestations of the defective product, and the therapeutic options for treating the disease.

The evolutionary cause of a disease is the speculative evolutionary story of how the disease arose and persists. For example, the evolutionary cause of a genetic disease is a speculation about how the disease state survived 'natural selection' and speculation about several proposed interactions between the disease and the host.

With that in mind, let's look at Coyne's post:

I was once down on the practical uses of evolution: I thought of the discipline more as a way to understand the world than to improve it. But I’ve changed my mind, largely at the instigation of Dave Hillis at the University of Texas at Austin, who has enlightened me about the real applications of evolution in medicine.

"Applications of evolution in medicine" is perhaps a bit optimistic. Evolutionary explanations of disease states are remarkably speculative, perhaps even more so than evolutionary explanations of biological origins. It remains unclear how such speculation can become 'applications' in medical science, which after all, is the paradigm of applied science.

An analogy would be the attempt to apply the multiverse theories of cosmology to bridge construction.

At the meeting yesterday there was an all-day symposium on “Darwinian medicine” (DM). This is the discipline that studies not only how the evolution of pathogens helps us understand disease (antibiotic resistance in bacteria is, of course, the classic example), but also how human evolution affects not only our susceptibility to disease, but explains some of our symptoms (fever, for example, may be an evolved adaptation to kill pathogens, and so you might want to hold off reducing mild fevers).

Fever is a good example of the pros and cons of "applying" evolutionary speculation to medicine. We know a great deal about the influence of fever on the immune system and on microorganisms. The wisdom or folly of reducing fever is assessed by the actual proximate knowledge of the relevant pathophysiology, not by evolutionary stories about fever. 'Does reduction of fever help or hurt recovery from infection' is the relevant question, and it is entirely a question of proximate causes.

The evolutionary speculation about how fever arose-- 'organisms that survived infections by mounting fever were more reproductively successful than organisms that didn't mount fever and thus didn't survive infections-- is probably true, and just as probably tautological. But the evolutionary speculation is based on the proximate (scientific) understanding of fever and of resistance to disease. The evolutionary speculation adds nothing new to the proximate explanation.

Of what application is evolutionary speculation to medicine, above and beyond the scientific proximate explanation?

Nesse is perhaps the most enthusiastic advocate of Darwinian medicine.

He's a passionate salesman.

Nesse’s talk was called “What evolutionary biology and medicine offer to each other, and reflections on George Williams.”

George Williams was a colleague of mine here at Stony Brook who passed away recently. I didn't know him personally, but he was very well-liked and is highly respected.


[Nesse] began simply by recounting some statistics: how few evolutionary biologists there are on medical school faculty: almost none, but that’s not much of a surprise.

Well it should be a surprise. If "nothing makes sense except in light of evolution" and if an evolutionary understanding of disease is important to medicine, why aren't there any evolutionary biologists in medical schools? It would seem that the utter absence of a scientific discipline for the past half-century might imply that the discipline didn't offer much to practice and research. Seems kind of obvious.


More surprising is how little evolutionary biology actually gets into med-school curricula, despite its importance for medicine.

The reason that little evolutionary biology actually gets into med-school curricula is because of its unimportance for medicine. There's no paradox at all.

Most schools teach things about antibiotic resistance, more or less because they have to...

Medical schools teach quite a bit about antibiotic resistance because such knowledge is essential to medicine. Doctors deal with antibiotic resistance daily, and virtually all research on this vitally important issue is done by medical researchers in medical schools and in pharmaceutical companies. Evolutionary biologists do very little research on antibiotic resistance.

Medical schools teach and do research on antibiotic resistance because they are the experts on it, not (pace Coyne) "more or less because they have to."

Coyne's an arrogant jerk.


but other aspects of DM aren’t often taught in medical school: things like “adaptive” human symptoms of disease, or things that pathogens do to facilitate their own spread (the fact that malaria makes you prostrate, for instance, may actually be an adaptation of the malaria parasite to facilitate its spread; you’re more likely to be bitten by a mosquito, who transmits the parasite, if you’re laid out flat in bed).

Coyne uses the amusing speculation that malaria makes victims prostrate because the immobility of the victim helped the mosquitoes lite and spread the disease. "Natural selection"? No. Narrative gloss.

Set aside the vacuous science-- how (why) exactly would you test the theory that malaria makes victims motionless because it helps spread the disease? Do 'just so' stories advance medicine? In what way would Coyne's "evolutionary cause" advance understanding or treatment of malaria? Make beds that shake so the mosquitoes can't lite? ('go 'round again, Frank, it's too choppy to land!'). Order patients in the midst of a malaria relapse to do aerobics? ('what are all of these Richard Simmons videos doing in the malaria ward?')

What Darwinian medicine tripe.


Nesse gave six evolutionary reasons why humans are still susceptible to disease, despite the adaptive advantages of being resistant to disease:

I'll cover all six, in ensuing posts.

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