Sex is any process that mixes genes from different individuals. - Olivia Judson

Evolution does not obey human notions of morality, nor is human morality a reflection of some natural law. The deadly sins would be different if they mirrored evolutionary no-no’s. Lust, for one, would be deemed a virtue; chastity would be deplored.

Indeed, natural selection discriminates against well-behaved losers.

If a proclivity for promiscuity is genetic, then yes, promiscuous behavior will become more common if loose females tend to have more children than their monogamous peers. That’s how natural selection works.