So go back in time with me to when the humans first evolved. Now as a male your god given responsibility was to make more humans because the life span was 25-30 years max and you want to spread your seed as much as possible so your instinct was to "get with" (͡° ͜ʖ ͡°) as many girls aa possible so there would be more humans on the planet. It remained instinct for thousands of years because the male brain loves novelty and naked chicks it loves new naked chicks.
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Edited by LahDsai: 6/3/2017 1:39:53 AMFemales can reproduce only once every 9 months. It's an investment and, therefore, evolutionary advantageous to be picky. Males can reproduce every four hours, give or take. It's a quantity game. This promotes competition, which helps females assess better potential partners and, in turn, makes them compete among themselves to secure superior partners. It is, however, also evolutionary advantageous (for both males amd females) to protect your progeny. This is why humans are typically considered socially monogamous (typically having one primary mating partner but potentially having flings on the side).