Monogamy is not an exclusively male evolutionary strategy. According to the zoologist Birgitta Tullberg, groups of female anthropoid primates who started off as harem-minders later evolved into groups of monogamous females. Meanwhile, the usual swelling and scents that would indicate that a female is ovulating and fertile disappeared over just a few generations. Why? To ensure males helped with caring for the offspring: if a male doesn’t know exactly when a female is fertile, he has to have sex with her continuously since he can’t tell when she is in heat. A male who sticks around can be more certain he’s the father. Female humans have evolved toward concealed ovulation too, to ensure paternal investment.
As a result, just as scissors beats paper, monogamous individuals beat harem-minders, be they men or women.
And, much like rock beats scissors, in some cultures being a “sneaker” (those who are sexually free floating, regardless of their legal commitments) beats being monogamous.