Ewald on the New Germ Theory
Wednesday, October 26, 2005
Ewald and Cochran have been creating a stir by
asserting -- with considerable success -- that not only is evolutionary
theory true (at least micro-evolution), but properly applied leads to the
conclusion that many so-called "hereditary diseases and defects"
are in fact caused by germs and viruses. The full story will be in upcoming
articles, but I got Cochran's permission to publish this much here.
For considerably more see
If you have any interest in biology and the future:
is by Paul W. Ewald
This commentary is by Greg Cochran. JEP
Ewald on the New Germ Theory
The idea is this: whenever some individual is way out at the edge of the distribution, or for that matter entirely off it, infectious disease is a strong candidate for the cause. If you just look at physical appearance, this is obvious enough; hardly anybody manages to look much like Quasimodo without having tuberculosis of the spine. This is particularly likely to be true if the surprising phenotype has been around a long time and is halfway common and/or deleterious There are and have been places where lots of people are blind well before old age - the cause is onchocerciasis, herpes stromal keratitis, trachoma or, in the olden days, smallpox. Infectious diseases. There are places where tens of percent of women are infertile or subfertile - mostly caused by infectious diseases like chlamydia and gomnorrhea. If you see someone whose legs look like huge rotting furniture, it's elephantiasis. We won't talk about LGV.
Mutations can have the same effect [socially interesting, biologically disadvantageous phenotypes] , but they're less common. People with achondroplasia, classic dwarfism, used to play socially important roles in European courts. Microcephalics and India-Rubber men ( Ehlers-Danlos syndrome) helped keep many a circus alive. People with Marfan's syndrome, a connective tissue disorder, are vastly overrepresented among top-rank volleyball players, but are subject to aneurysms in midlife. XY individuals with androgen insensitivity look female but are infertile - they have an unusual look that causes them to be greatly overrepresented among actresses and models. You know who I'm talking about. Male-female mosaics played an important role in the Olympics, before they were eliminated by genetic tests and before substantially equivalent outcomes in women could be achieved through the use of anabolic steroids. There is a particular family in Finland that has unusually high levels of red cells - they've produced an Olympic-quality cross-country skier, but they stroke out. These last few examples make clear how biologial weirdness can put you over the top in highly competitive situations.
Some socially interesting conditions are caused by a mix of mutational pressure and infection. In recent years, untill the rubella vaccine became widely used, about half of congenital deafness was caused by prenatal rubella infection, while the rest was caused by more than one hundred different mutations.
People with these problems sometimes fall into special social roles - not just in the circus. Blind men evidently make excellent seers, poets, and musicians. Deaf people have created an entire subculture, with their own language, Ameslan. A few high-achieving people such as Edison and Lord Rayleigh, may have been aided by their deafness.
So, on the same tack, some of the interesting variations in psychology seem likely to be caused by some kind of infectious organisms also, especially if they are more than rare, detract from reproduction, and have been around for some time. Just like being a hunchback (great at bellringing and pouring molten lead on louts) , some of these variants wil confer abilities or tendencies that are valued by society, or at least are noticed by society This is not a group-selection argument - we're not saying that the variants exist or are sustained through their contributions to society as a whole - but at least some of the time we're going to take biological lemons and make lemonade.
Tertiary syphilis used to be one of the major causes of mental illness and many people thought it made you more interesting. "Nietzsche is pietzsche" . There are other mental illnesses or errors of development that matter tremendously for certain jobs, certain kinds of creativity, but whose causes are as yet unknown. . Manic-depression is not rare and is culturally important. There's good reason to believe that most important poets have it, and a surprisingly high fraction of novelists. Manic-depression probably lowers your fitness quite a bit, on average. Sometimes prominent men with manic-depression have lots of kids, but most men with manic-depression are not prominent, and I think it can never be an advantage to women. So, even though it has pretty high heritability, manic-depression might be caused, at least in part, by some virus. I'm willing to _listen_ to arguments that it is some kind of frequency-dependent strategy, but I don't really believe it. Same for schizophrenia, except that it's worse for you than manic-depression, and probably less often associated with high creativity. But Godel is enough to make the point, all by himself. And autism-spectrum conditions - Richard Borcherds, Fields medalist, and a lot of other mathematicians.
Homosexuality? of course: biological disadvantageous, culturally consequential. Old and common enough to probably have an infectious origin. The low twin concordance (and neoDarwinism) makes strongly genetic explanations unlikely.
I don't think that every famous or especially creative person has something biologically unusual going on. I do think that this is true of a disproportionate fraction.
Further: in a generation or two, we're going to to be able to control all these things, mutational or infectious - at least in the wealthier countries. . Nobody's going to be manic-depressive. Nobody's going to have schizophrenia. No kids will be born deaf, and deaf culture will fade away. I think that not too long after we determine the etiology of homosexuality , we'll be able to prevent it, and almost all parents will. Forget Marfans, and dwarfism, and Ehlers-Danlos
The human race will be more uniform. This trend has already been underway for a long time - you don't see those entertaining paresis cases on the street anymore, congenital deafness is down by factor of two, blind beggars are scarce, Down's syndrome is getting rarer. Soooo... it might also be the cause that certain kinds of thinking become scarce, kinds of thinking that occasionally pay off. Even so, we'll do without. Damn few parents are going to choose to have a manic-depressive kid on the off-chance that he'll be a major poet someday.