Matt Ridley reviews a new book by Moises Velasquez-Manoff:
In a remarkable new book, “An Epidemic of Absence,” Moises Velasquez-Manoff draws together hundreds of such studies to craft a powerful narrative carrying a fascinating argument. Infection with parasites prevents or ameliorates many diseases of inflammation. The author briefly cured his own hay fever and eczema by infecting himself with hookworms-before concluding that the price in terms of diarrhea and headaches was too high.
I’ve touched on the “hygiene hypothesis” in these pages before. In its cartoon form the argument-that in a clean world our immune system gets bored and turns on itself or on harmless pollen-isn’t very convincing. But Mr. Velasquez-Manoff makes a far subtler, more persuasive case. Parasites have evolved to damp our immune responses so that they can stay in our bodies. Our immune system evolved to expect parasites to damp it. So in a world with no parasites, it behaves like a person leaning into the wind when it drops: The system falls over.
Moreover, just as brains outsource much of their development to the outside world-the visual system is refined by visual input, the language system can only develop in a language-using society — so the immune system seems to have happily outsourced much of its regulation to friendly microbes. Without them, the immune system becomes unbalanced.
[. . .]
One of Mr. Velasquez-Manoff’s most surprising chapters is on autism, a disorder that almost exactly parallels asthma in its recent rise among affluent, urban, mainly male, disproportionately firstborn people. Better diagnosis explains perhaps half the rise, but the brains of people with autism are often inflamed, and there’s anecdotal evidence that infection with worms or viruses can tame autistic symptoms, at least temporarily.
