Hi, Shinigami.
Welcome to EvC!
From a societal/legal standpoint, I agree with Mr Jack and Perdition.
But, from an evolutionary perspective, you'll need to be a little more specific. For instance, it will change how much it "makes sense" based on whose perspective you're speaking from.
I don't think either polygyny or polyandry makes since for humans, unless we assume unequal mortality rates between the sexes. But, in terms of gross reproductive output, polygyny makes sense biologically from the male's perspective, but polyandry doesn't make sense biologically from a woman's perspective. This is because females are a limiting resource, which means that the only way to increase reproductive output is to increase the number of females.
This means that males can increase their reproductive output by increasing the number of sexual partners, but females can't.
In fact, the competitive nature and "commitment issues" of men, which women are fond of teasing us for, are indications that polygyny has been an important shaping influence on the evolution of human men.
For a woman, it makes more sense to pick a single partner and keep him close, because a dedicated partner can share the burden of child-rearing and improve the child's chance of survival. They seem to have prevailed on us, because they managed to get us to found stable communities and monogamous pair-bonds.
In our social environment, the stability and security afforded by monogamy makes more sense than the one-sided reproductive benefits of allowing men to sow their wild oats. So, monogamy is the way to go.
-Bluejay (a.k.a. Mantis, Thylacosmilus)
Darwin loves you.
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