IMO, humans, male or female, seek the best mate. &quot;Best&quot; is subjective but usually easy to understand. Men want youthful, beautiful women whereas women want strong, resourceful men.<p>In enforcing monogamy, we ensured that male got what they wanted (a young woman) and now, that male can focus his attention on work. This worked well for women too (if they had a choice of male) since they now have a partner as well. Adultery was looked down upon to preserve the &quot;sanctity&quot; of this 1:1 relationship. This also kept men working hard to build the society (since they didn&#x27;t have to deal with family issues much) and women preserved morality and guarded home upbringing.<p>Today, since adultery&#x2F;serial monogamy&#x2F;polyandry&#x2F;polygamy etc. is a joke and widely &quot;accepted&quot;, there is no incentive to get married. So many 18-35 waste their youthful lives just dating, dating, meeting jerks, partying, jumping from partner to partner....instead of focusing on building a REAL stable relationship.<p>By early 30s, most folks are sick of dating and all illusions of love are gone.<p>Monogamy is not practical without heavy penalties on non-monogamous relationships.