The appendix seems to be a counterexample to this philosophy of evolution. Useless body parts exist. What are the chances there are no useless behaviors? (By "useless" I mean "no fitness advantage.")
Not sure I agree wholly with the GP, but recent theories suggest that the appendix does in fact serve a useful purpose. It can act as a reservoir for gut bacteria that are necessary to our digestive health. It helps repopulate gut flora when they get wiped out by illness (often caused by other bacteria) that causes a bad case of the runs.
