Matt Ridley‘s idea here is definitely provocative, but I can’t help think there might very well be something to it.
Matt Ridley on ‘An Epidemic of Absence’ – WSJ.com: Your great-grandparents faced infectious diseases that hardly threaten you today: tuberculosis, polio, cholera, malaria, yellow fever, measles, mumps, rubella, smallpox, typhoid, typhus, tapeworm, hookworm…. But there’s also a long list of modern illnesses that your great-grandparents barely knew: asthma, eczema, hay fever, food allergies, Crohn’s disease, diabetes, multiple sclerosis, rheumatoid arthritis. The coincidence of the rise in these “inflammation” diseases, characterized by an overactive immune system, with the decline of infection is almost certainly not a coincidence. Natural experiments in recent decades support the idea that while modern hygiene defeats infection, it also promotes allergy and autoimmunity. Finns isolated in an impoverished Soviet province had more parasites and fewer allergies than Finns in Finland. Swedes in clean Stockholm had three times as much asthma as Estonians in smoky Estonia. Ethiopians and Gambians got allergies when they lost their intestinal worms. Growing up on a farm greatly cuts allergy risk.
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.
There’s also a link between inflammation during pregnancy, caused by allergy or autoimmune disease (or chronic, low-grade infection), and autism in the child. Acute infections during pregnancy, on the other hand, correlate with schizophrenic symptoms, which may be why schizophrenia is growing rarer while autism grows more common.