It's so weird the appendix isn't the go to example instead of whiteness and milk drinking....

Up until a few hundred years ago it was vital as a reserve for gut bacteria when everyone was always getting dysentery and diarrhea. It still burst occasionally but it was a net positive. People without one likely died before it would have burst.

Then we got indoor plumbing and food safety, we stopped needing it so much which changed the evolutionary pressure. People without one never had it burst, so it flipped.

Then we discovered how to do an appendectomy ~300 years ago, and removed all the evolutionary pressure.

So it'll stay a random percent where some people do and some don't.

But everybody always wants to talk about whiteness and milk drinking