It's apparently been noticed for some time that children who grow up on farms are less likely to have asthma than other rural (and urban) dwellers.
This ties into the "hygiene hypothesis," the idea that a lack of exposure to microbes and parasitic worms somehow primes the body for auto-immune disorders like asthma and allergies. A new study suggests that this may be due to the diversity (or composition) of microbial communities that farmboys (and girls) are exposed to, rather than the quantity. (Unfortunately, I don't have access to the original NEJM article.)
As a former environmental microbiologist, I love the idea that culturing robust and complex microbial communities on our bodies is somehow optimal for our health - though I think the jury's still out as to what extent this is actually true. Ever since grad school, I've been waiting to hear someone take the next logical leap and claim that toothbrushes destroy our co-evolved dental flora, leading to cavities.*
I'll be interested to see if anyone tries to take this idea that far...
h/t: as described by The Great Beyond
*I've long been baffled by the rate that many of us rack up cavities despite intensive dental care. Our ancestors must have been toothless by 40.