Your guts bugging you? Turns out that's a good thing. Until recently, the appendix has had a reputation as a shiftless organ with no known modern function, but evolutionary biologists now have a different idea -- that it functions as a storage unit for good bacteria. They argue the good bacteria hangs out in the appendix until needed to replace ones flushed out by diarrhea or other nasty gut-bug killers. When the gut gets flushed out, the appendix -- which is lined with immune system tissue -- releases the good bugs back into the intestine. Today's improved sanitary conditions leave our immune systems twiddling their thumbs to some extent, so the appendix is not needed as often as in the days when our ancestors were, say, eating raw meat and drinking water from streams. Without enough immunity battles to fight, and perhaps too much exposure to anti-microbial hand washes, the body begins picking battles with allergies and autoimmune disorders. Hence all the recent studies that say eating dirt is good for kids.