In the non-human animal kingdom (as in the human one) social monogamy and sexual monogamy are not the same thing. "Mating for life" very rarely results in totaly sexual monogamy. We used to think that a lot of birds were monogamous but DNA technology demonstrated that offspring or some offspring quite often came from a papa bird who was not the one helping to tend the nest.
With the onset of patriarchy, paternity becomes central, and the only way to ensure that is to coerce and essentially imprison women to keep them from other mating opportunities, which they were used to regularly engaging in (since they didn't yet have DNA technology). Patriachy also sets up the man as the head of the family, something that was not so before, and is not inherently the case in polyamory. Not every single last monogamous relationship is rife with patriarchy, but pretty close. I say this from having been on both sides of the coin. For 20 years I thought we had a fairly egalitarian mongamous relationship. It was only when we opened up our marriage that we both began to see all the different subtle ways that we had unconsciously bought into patriarchal norms and roles - things that are just not an inherent part of polyamory because there's no pre-set rules. Everything has to be worked out and negotiated.
I stand by my assertion that sexually monogamous marriage is a patriarchal structure.
“From Sumer to ancient Athens and Rome, medieval Europe, the Islamic world and traditional China, rigidly male-dominated societies, argues historian Riane Eisler (The Chalice and the Blade), relied on pain or the fear of it to maintain hierarchical relations of dominance and submission. Patriarchy, she believes, represses sexuality, distorts the natural bonds of erotic pleasure and love between men and women and diminishes women’s status. Drawing on archaeological evidence and Paleolithic and Neolithic art, Eisler argues that prehistoric societies were relatively free of the domination, exploitation and misogyny that have marked Western societies up to the present. She emphasizes that Christianity’s hostility toward sex and, particularly, women’s sexuality has conditioned men and women to accept coercion and repression.Eisler outlines a new sexual ethic that aligns pleasure with our capacity to feel and act empathically. Her visionary, passionate scholarship is a revealing psychosexual exploration of love and power relations.” Sacred Pleasure: Sex, Myth and the Politics of the Body — New Paths to Power and Love; Riane Eisler
