In the last few years, two articles — one in Journal of Theoretical Biology, the other in Journal of Evolutionary Biology — by William Parker, a professor of surgery at Duke, and others have argued that the function of the appendix is to harbor bacteria. If diarrhea washes out your intestines, bacteria safely hiddne in the appendix can repopulate them. (A theory supported by the position of the appendix — roughly in the middle of your intestines.) That makes perfect sense.
The connection with my umami hypothesis is that both assume that the foreign bacteria within us are precious and endangered. (My umami hypothesis says we need to consume plenty of bacteria to be healthy and that our food preferences help us do so.) The precious part is widely accepted; it’s the endangered part that’s new. If we need bacteria so much, why should they be endangered? We need our eyes; they aren’t endangered. My answer is that to protect bacteria carries a cost: The most hospitable the digestive system becomes to bacteria, the less effective it will become at everything else, including digestion. And bacteria were/are cheap. Rather than protect them, the system has been shaped to require them. Just as gas-guzzling cars evolved when gas was cheap. Making cars more gas-efficient will make them less efficient at other functions, such as signaling status.
Thanks to Kathy Tucker, James Andrewartha, and James Lucoff.