Posted by Harriet Hall on July 3, 2012 ( Comments)

3 years ago I wrote an article critical of evolutionary medicine as it was presented in a new book. Recently a correspondent asked me if I thought another book, Why We Get Sick: The New Science of Darwinian Medicine, by Randolph M. Nesse, MD and George C. Williams, PhD, was a more reasonable approach to the subject. It was published in 1994 and got good reviews from respected scientists like Richard Dawkins (Buy two copies and give one to your doctor.) and E.O. Wilson (bringing the evolutionary vision systematically into one of the last unconquered provinces). I was able to obtain a copy through interlibrary loan.

The book was interesting and gave me some things to think about, but it didnt convince me that Darwinian medicine is a new science, that its existence as a separate discipline is justified, or that its unique approach offers any real practical benefits for improving medical care.

Why do we get sick? A simplistic view of evolution holds that it systematically eliminates any factors that decrease fitness for survival. So why does disease persist? Why didnt we evolve to be fit enough to never get sick? Because evolution is not a straightforward process.

Evolution is complicated.There are countless design flaws in the human body. For instance, we are subject to choking because of the crossed anatomy of our respiratory and digestive systems. Nesse and Williams point out that it would be more sensible to relocate the nostrils to somewhere on the neck, but that just aint gonna happen. Evolution is limited by pre-existing patterns and has to make compromises. Historical accidents result in developments that are far from optimum. A useless or even a harmful gene may be perpetuated because it is linked with a beneficial gene. We are in an arms race with pathogens: we evolve defenses and they evolve ways to overcome those defenses. Natural selection made us fit as small groups of hunter-gatherers on the plains of Africa. We are specifically adapted to Stone Age conditions. We face very different environments today where our evolved traits can be counterproductive.

Who are the fittest? Fitness doesnt mean fitness for the individuals welfare, but fitness for propagating the individuals genes. After the individual has reproduced, diseases of old age dont affect evolutionary fitness except in minor, indirect ways. (Grandparents past reproductive age can contribute to the survival of descendants by helping with childcare and providing accumulated knowledge and wisdom.)

Nesse and Williams differentiate between proximate and evolutionary explanations: heart attacks are caused by cholesterol deposits in the arteries, but they want to know why evolution shaped us to deposit cholesterol, crave fat, over-eat, etc. I want to know, too; but Im not so certain that knowing will reduce my chances of a heart attack.

Are evolutionary explanations just pseudoscientific equivalents of Kiplings Just-So Stories? They argue that they are not. They give the example of morning sickness. It has been hypothesized that the nausea, vomiting, and food aversions of early pregnancy are beneficial because they protect the vulnerable fetus from dietary toxins. This would predict that morning sickness preferentially results in avoidance of foods most likely to harm the fetus. This is a testable prediction and there is some evidence to support it; but there is no way to prove that this is the true explanation or the only one. They suggest that suppressing morning sickness might increase the risk of congenital defects. But there is no evidence for that. They recommend that women respect their nausea and remember that it may be beneficial. (It would likely decrease your survival prospects if you said that to your wife while she was throwing up for the umpteenth time!) They admit that relieving suffering is important too, but they recommend that any anti-nausea medicine should be carefully evaluated to make sure it doesnt cause any harm. Of course, we already do that for all medications used during pregnancy. I fail to see how evolutionary thinking adds anything to the care of pregnant women. In fact, I can see how it might result in unnecessary worry and suffering.

They suggest that sexual reproduction is an advantage because the genetic variations increase survival when a population faces an infection. As supporting evidence, they cite studies showing that asexual reproduction is more frequent in species and habitats with fewer parasites. Maybe. Correlation doesnt prove causation.

They speculate that schizophrenia must persist in our genomes because it offers some advantage that balances the severe costs. They even have a creative hypothesis about why we sleep.

The rest is here:
Do We Need Evolutionary Medicine? Science-Based ...