Hamilton, Swan and Moldoff create the Superman/Batman story in World’s Finest 151 (Aug. 65), a story I always found very silly, but I know a large number of people who just love it.
A Kryptonian evolution ray has been discovered by Superman, but as it has been turned into kryptonite, he needs Batman to help him examine it. Batman accidentally causes the ray to evolve him into a future man – cold and emotionless, with a giant bald head. This makes him evil, and he turns the ray on Superman, devolving him into a caveman.
Then it’s brains vs brawn for the rest of the tale. Caveman Superman bursts into the Daily Planet building, grabbing Lois Lane by the hair and carrying her off to make her his mate. Fortunately, Batman interrupts before Lois gets raped.
Batman heads into the far future, to be with people like him, but Superman follows and drags him back to the prehistoric era.
It’s actually Krypto who saves the day, jumping in front of the ray to save Superman. Batman winds up getting turned back to normal, and reverses the ray’s effects on Superman and Krypto.