(another own goal, of course.)
There he goes again. Creationist neurosurgeon Michael Egnor’s latest post over at the Discovery Institute’s Why’s Everybody Always Picking On Me blog may have actually reached a new standard for missing the point. And, as both my loyal regular readers know, that’s not an easy mark for Egnor to hit.
The current contender is his latest post in a back-and-forth that he’s been having with PZ and Orac. Once again, Egnor is attempting to argue that evolutionary biology has not provided any useful insights to the field of medicine. That much is familiar ground. What’s new this time is the hypothetical that he’s dredged up in an attempt to prove his point. His hypothetical is long and involved, which should provide you with your first warning that the argument is perhaps not as sound as he believes:
What I’m arguing is that the truth or falsehood of Darwinian stories is of no tangible value to medicine. Consider the following example.
I would suspect that careful epidemiological studies of the British population would show that the prevalence and incidence of spina bifida increased following World War One. To my knowledge, this has not been investigated, but it would make sense if it were true, for the following reasons:
Britain suffered enormous casualties during the Great War, as did many other European nations. (I’m just using Britain as an example). It has been said, with asperity, that Britain lost a generation of men on the Western Front. Britain suffered 2,300,000 war casualties — forty four percent of mobilized men, with 703,000 men killed in battle or by disease. On just one day — July 1,1916 — 19,240 British soldiers died in the battle of the Somme. The young men who died were the best of their generation — healthy, and by definition capable of meeting the rigorous physical standards required for military service.
Of course, other British men with debilitating genetic disorders, such as men with spina bifida (which renders the afflicted congenitally paralyzed), were not in the trenches that day, because they were physically unfit for military service, or at least service on the front lines as infantrymen. It’s safe to say that military age British men without spinal bifida were at greater risk of death in the war than were military age British men with spina bifida. Whatever the impediments faced by people with spina bifida — and they face many impediments — they were not called to serve and die in the trenches.
Spina bifida would then be a fine example of an environmental adaptation; it was protective against “acute lead poisoning” — protective against being mowed down by German machine gun fire on the Western Front. So, assuming for argument’s sake that my hypothesis about the post-war epidemiology of spina bifida is true, the genes that give rise to spina bifida conferred a selective advantage on young British men in the period 1914 to 1918, and the differential survival (and reproduction) of that age cohort would explain a (hypothetical) increase in the incidence and prevalence of spina bifida in England in the post war period.
Where to begin?
We could begin with the inanity of his example. Spina bifida is still a very serious condition that carries with it a significant risk of early death – and that’s despite the development of effective neurosurgical techniques. A study of babies born with spina bifida in the UK between 1965 and 1972 reported an overall 5-year survival rate of about 37%. One of the symptoms that would have been fairly common in the surviving males is impotence. When you add in the fact that there seem to be factors beyond heredity involved, I’d doubt that there was any measurable spike in the incidence of the disease. Given the high mortality and rarity of the condition, I’d also be surprised if there was even a noticeable difference in the prevalence.
(For those of you who are not familiar with the technical use of the terms, prevalence refers to how common a particular condition is in a population, while incidence refers to how frequently new cases turn up.)
Ultimately, though, dealing with the inanity of the example is unnecessary. Egnor cheerfully admits that he doesn’t actually have any idea at all if his example is actually real:
Interesting vignette, if true. I haven’t a clue about its veracity.
Someone less kind and charitable than myself might point out that the last three words in that quote were entirely unnecessary, but let’s move on.
We could also start things off by focusing on Egnor’s characteristic lack of intellectual integrity. Orac cited both sickle-cell disease and antibiotic resistance as examples of cases where an understanding of evolution has provided useful medical knowledge. Both of these have been pointed out to Egnor before. In fact, they’ve been pointed out to him many, many times.
Egnor has, yet again, decided to ignore the examples that were presented to him. Instead of facing those issues head on, he cooked up an unlikely and convoluted hypothetical that – by his own admission – may have absolutely no relationship whatsoever to reality. Declining to face reality in favor of tilting with your own personally invented reality may not necessarily be the mark of a psychiatric pathology, but it’s definitely not the mark of intellectual honesty, either.
But we can ignore the lack of integrity, too. After all, the fact that Egnor is apparently incapable of facing reality is not in and of itself proof that he is actually wrong.
Instead, let’s assume that the hypothetical is actually true, and look at the argument that he’s trying to make:
Interesting vignette, if true. I haven’t a clue about its veracity. But here’s the crux of my argument: military history, which is the basis for understanding this hypothetical blip in spina bifida in England in the 1920’s, is obviously not essential to medical education, research, or practice as relates to spina bifida. Military history may, if my inference is true, offer an explanation for changes in population frequency of the spina bifida genotype and phenotype in post-war England, but it’s not in any way essential or even relevant to the medical management or understanding of spinal bifida. It’s tangential at best, and such historical vignettes, interesting and perhaps of importance to historians, are of no practical use to physicians or medical scientists.
The analogy between my military history hypothesis and Darwinian theories of the origins of disease is quite close. Darwinian explanations for disease are historical vignettes. Darwinian stories are “military history” hypotheses about the ancient struggle for survival, a characterization long employed by evolutionary biologists, and I think an apt characterization.
Here’s the funny thing about his argument: a basic understanding of the principles of evolutionary biology is actually more important to understanding the “hypothetical blip” in the incidence of spina bifida than military history. In fact, there are cases where an understanding of evolutionary biology can be combined with demographic factors (like a war) to inform us about the underlying causes of a disease.
Those are actually two separate arguments, so let’s take them one at a time. We’ll start with the asinine assertion that military history is all that informs us about the cause of the increased incidence.
In fact, our understanding of military history can only inform us of the cause of the (hypothetical) increase if we already understand some basic principles of evolution, and some basic facts about the disease. At a minimum, we would need to know that spina bifida patients are typically unsuitable for military service, that there are hereditary factors involved in causing spina bifida in the first place, and that differential survival among individuals carrying an allele will affect the proportion of that allele in the next generation.
The first two factors relate to our understanding of the condition. The third is nothing more nor less than the central principle of evolutionary biology. Only one of those three factors is connected with the military in any way. Military history provides us with an explanation for the differential survival, but that’s all. If we didn’t know the other stuff, the war alone would provide absolutely no explanation for the change.
Egnor has, in short, provided another example of why an understanding of evolutionary biology is essential to the medical field known as epidemiology.
But (as the television salesman says) wait! That’s not all!
Let’s take Egnor’s hypothetical and add an element. Let’s assume, hypothetically, that we have absolutely no idea of whether or not spina bifida has any heritable component whatsoever. In such a case, the demographic changes caused by the war could be combined with our understanding of the effects of spina bifida and evolutionary biology to help answer that question.
If we knew that a particular condition rendered sufferers ineligible for military service, and saw a dramatic spike in the incidence of cases of this condition in the years following a bloody war, an understanding of evolutionary biology would allow us to make several predictions. First of all, we could predict that the condition in question was not so severe as to drastically reduce either survival to reproductive age or capacity for reproduction. Second, we could predict that the condition does, in fact, have a substantial hereditary component.
In a case like that, as in Egnor’s slightly simpler hypothetical, evolutionary biology can help medical understanding.