Monogamy was “created” because it creates a familial environment that is the best platform for a mature, fulfilling, and happy life.
It gives the woman a sense of security. It keeps the man from bending to his natural will to have multiple (multiple) partners.
Each of the above individual instincts of the sexes, if not met or tempered, will lead to an unhappy, or unbalanced life.
Man is not monogamous, but Civilized Man is.
Funny how ‘Evolution” and “Nature” and “natural selection” “evolved” so many trillions of cells and millions of favorable behaviors all by “accident” and independent random changes in the DNA of quadrillions of random different creatures and plants and species, but there is no such thing as an ‘intelligent designer” ......
The alternative leads to violence and it probably wasn’t over children, in most cases. Early man didn’t grasp the concept of paternity. They fought over women and that led to instability and hunger all around.