you'll often see people talking about the distant past, misinterpreting a genetic property of humans, namely that there are more females than males in the human genome. this, simps and broscience pledditors think, means that in the early paleolithic the world was populated by stone age chads who all ran around with a harem of stone age thots on their backs. in reality this genetic property is from a near extinction event, where so many men died that humanity almost died out. the only way to preserve a higher ratio of one sex in the genome is by close incest. so that's what that means. sometime hundreds of thousands of years ago humanity was so close to dying out that women had to reproduce with their fathers and brothers in lack of other men. as you say, monogamy has been the recipe for success for humans for at least tens of thousands of years, probably more.
Norway