We humans have many vestigial features proving that we evolved. The most famous is the appendix.
There are only two perfectly useless things in this world. One is an appendix and the other is Poincaré.Georges Clemenceau
I have noticed that doctors who fail in the practice of medicine have a tendency to seek one another's company and aid in consultation. A doctor who cannot take out your appendix properly will recommend you to a doctor who will be unable to remove your tonsils with success.ernest hemingway
Progress: The process whereby the human race has got rid of whiskers, the vermiform appendix and God.h. l. mencken
Dividing by zero...allows you to prove, mathematically, anything in the universe. You can prove that 1+1=42, and from there you can prove that J. Edgar Hoover is a space alien, that William Shakespeare came from Uzbekistan, or even that the sky is polka-dotted. (See appendix A for a proof that Winston Churchill was a carrot.)