The way I see it:<p>Polygamy:<p>Some men having a chance at a huge family.
Most women having a chance at a family, but with a shared husband.
Many men having no chance at a family at all.<p>Monogamy:<p>Most men having a chance at a family.
Most women having a chance at a family.<p>Now consider that the more one has to lose, the better behaved one is.  When men have a chance for a family, they&#x27;ll do what is needed to make the attempt for a family (normally being productive members of society), after which they get far more needs met than when alone (consider that loneliness is quite dangerous for a person) and they likely have more to lose (especially if they have children).  Thus they are more behaved.<p>But in a polygamous society, there is far less of a chance.  So more men decide to not play by the rules.  They will seek out more dangerous means to meet their immediate needs.<p>All this being said, it isn&#x27;t the marriage that matters.  It is the family that does.  A society that only allows monogamy on paper, but which allows a polygamous marriages, and where a divide begins to exist meaning that you have many men without a chance of having a family will have the same issues.<p>Also, I&#x27;m not to sure what happens when many women don&#x27;t have a chance for a family.  While one might think it would work the same, there are a few key differences.  A man can be responsible for multiple simultaneous pregnancies, but a woman cannot.  A woman has, historically, had a level of assurance of the legitimacy of their children that a man does not, and on average men tend to be more physically powerful than women.  Also of note is that those last two factors stop being a significant difference with technology (paternity tests and guns being respective examples), so historic data may not fit what trends we will see in a technologically advanced society.  (To say nothing of technology increasingly being able to meet a person&#x27;s needs, which will increasingly make it harder to plot future events based on past data.)