A Blind Bargain (1922)

In return for money and medical aid for his invalid mother, struggling author Robert Sandell agrees to subject himself to experiments by Dr. Lamb, who claims he is trying to extend the human lifespan. Despite warnings from the doctor's wife and a hunchbacked assistant, Robert allows himself to be strapped to an operating table, whereupon he learns the true nature of the surgeon's experiments: To prove the theory of evolution by devolving his human subjects into an approximation of their simian ancestors. However, before Dr. Lamb can proceed, the hunchback un-cages another victim, an ape-man, who crushes Dr. Lamb to death.