I heard a thing that there is a midrash somewhere that people were acting really really bad, like animals. So Hashem said, if you want to be like animals, I’ll make you into animals. And slowly they started changing into monkeys.
So in fact it is true that we share a common ancestor: the human!
(It could be that it was by Dor Enos they might’ve started looking like monkeys but I’m not sure)