A man died and went to Heaven. There were thousands of other people there. They were all naked and all looked as they did at the age of 21. He looked around to see if there was anyone he recognised. He saw a couple and he knew immediately that they were Adam and Eve.
How did he know?
When a baby is born the umbilical chord is cut and it falls off, but it leaves a belly button. The couple he saw had NO BELLY BUTTON. The only humans never to be born from a womb were Adam and Eve. Hence he immediately knew they were indeed Adam and Eve. The real clue given in the problem itself is that all were naked!!