Counter to what many Americans believe, polygamy is not unnatural. According to Psychology Today's Michael Price, throughout history, "polygamy was permitted in the vast majority of cultures."
There's an evolutionary argument to be made for at least men taking on more than one wife. Husbands would then be able to reproduce at a quicker rate than if they were to have a single partner.
Price continues his argument, pointing out America's obvious bias on the topic. According to Price, American pop culture tolerates "de facto polygamy" on a daily basis. If we see it in our celebrities and idols, why not make the institution legal?
...although Western culture remains officially monogamous, it tolerates de facto polygamy in many forms. For example, serial monogamists like Donald Trump and Larry King divorce older wives to marry younger ones, which serves to monopolize the fertile years of multiple women (the same thing that polygamy would accomplish). Celebrities like Hugh Hefner and Charlie Sheen live openly with multiple girlfriends, and various male athletes, rock stars, and actors accumulate hundreds or thousands of sexual partners.
In light of the cross-cultural evidence, then, the question of what kind of marriage system emanates most directly from evolved human mating psychology does not appear to be a very challenging one. That system is polygyny.
Regardless of the traditionalist view that a polygamous arrangement is improper at best and immoral at worst, legalizing the practice is also impractical. The Atlantic's Conor Friedersdorf says that he would accept anyone engaged in a group relationship on a social level, but not on a legal one. He explains:
But I think it would be imprudent to include their arrangement in civil marriage, with its incentivizing benefits, because if group marriage were to become normalized and spread beyond a tiny fringe the consequences for society could be significant and negative.
Furthermore, legalizing polygamy would "require altering core features and benefits that presently make up civil marriage." Friedersdorf brings up a number of questions: Would multiple spouses be allowed on one spouse's company insurance plan? Would you be able to sponsor multiple spouses to come to the U.S.? Who would make medical decisions for each spouse? The list goes on.
Politico's Fredrik Deboer makes the argument that if marriage is not contingent on gender, then why must marriage be confined to two people? Meaning, if the country has moved away from the idea that a marriage can only be between a man and a woman, claiming reproduction as the scientific reason for such a practice, then all other kinds of unions must be on the table–even those between groups of people. Deboer writes:
Polyamory is a fact. People are living in group relationships today. The question is not whether they will continue on in those relationships. The question is whether we will grant to them the same basic recognition we grant to other adults: that love makes marriage, and that the right to marry is exactly that, a right.
Deboer leaves his readers with a call to action:
Given that many of us have argued, to great effect, that deference to tradition is not a legitimate reason to restrict marriage rights to groups that want them, the next step seems clear. We should turn our efforts towards the legal recognition of marriages between more than two partners. It’s time to legalize polygamy.
According to another Politico correspondent Jonathan Rauch, Deboer's argument could not be further from the truth. In Rauch's opinion, equating the case for the legalization of gay marriage in the U.S. to the case for legalizing polygamy is a non-sequitur. After debasing the many assumptions Deboer and many others make, he points to the dangers polygamy might hold:
Here’s a 2012 study, for example, that discovered 'significantly higher levels of rape, kidnapping, murder, assault robbery and fraud in polygynous cultures.' According to the research, 'monogamy's main cultural evolutionary advantage over polygyny is the more egalitarian distribution of women, which reduces male competition and social problems.'
Beyond the dangers that might await a modern polygamous America, the nature of these relationships also affects the children born from them. The study showed that monogamous relationships were more beneficial for children:
The study found that monogamous marriage 'results in significant improvements in child welfare, including lower rates of child neglect, abuse, accidental death, homicide and intra-household conflict.' And: 'by shifting male efforts from seeking wives to paternal investment, institutionalized monogamy increases long-term planning, economic productivity, savings and child investment.'