...human beings are not naturally monogamous but rather have been explicitly designed by natural selection to seek out ‘extra-pair copulatory partners’—having sex with someone other than your partner or spouse for the replicating sake of one’s mindless genes—then suppressing these deep mammalian instincts is futile and, worse, is an inevitable death knell for an otherwise honest and healthy relationship.Let us for the sake of discussion grant that human beings, at least male humans, are not naturally monogamous (I happen to believe that that's true. Men have to be taught to value monogamy). What are the implications of this for the future of marriage once we remove the legal barrier to homosexual marriage? If the natural state of humans is polyamory and if in our enlightened times we decide that the gender of the individuals entering into marriage no longer matters, what reason could there possibly be for saying that the number of people in the marriage matters?
Bering gives us a peek at the future debate. It will go something like this: Polyamory is a natural urge. To stifle peoples' natural urges is oppressive. Therefore it is oppressive for a society to deny people the right to form unions of any number of people they wish.
Once we've accepted the proposition that the gender of the married persons doesn't matter there'll be no basis for resisting the argument that the number of people in a marriage shouldn't matter either. And once we acknowledge that polyamorous marriages should be permitted for those who desire them, marriage will cease to have any real meaning or significance and will probably cease to exist.
Bering doesn't think that people will really want to form group marriages because, human nature being what it is, jealousy will obtrude forming an insurmountable obstacle. This is, in my opinion, naive. Polyamory has existed in various permutations throughout human history, and there will certainly be those who will wish to have it legitimated by the state once the philosophical and religious objections have been bulldozed out of the way by same sex marriage. Whatever people can do some will surely do. To think otherwise seems to reflect an inadequate understanding of human nature, and I'm surprised that a research psychologist doesn't recognize this.