It only really became taboo due to religion and the associated oppression of women. Humans, for the vast majority of the time they existed, were largely free r

It only really became taboo due to religion and the associated oppression of women. Humans, for the vast majority of the time they existed, were largely free range. Lots and lots of sex. I assure you, hunter gatherers were not monogamous suburbanites who attended their white Christian church.