|The Peasant Wedding. By Pieter Brueghel the Elder (1526/1530–1569) - Google Art Project: Home – pic Maximum resolution., Public Domain, https://commons.wikimedia.org/w/index.php?curid=20361036|
We have evidence that exogamous monogamy with a nuclear family was practiced in Germanic Europe 4,600 years ago, well before the introduction of Christianity.
Henrich et al. note that
"While the roots of the package of norms and institutions that constitute modern marriage can be traced back to classical Greece and Rome [6,7], the global spread of this peculiar marriage system  has occurred only in recent centuries, as other societies sought to emulate the West, with laws prohibiting polygyny arriving in 1880 in Japan, 1953 in China, 1955 in India and 1963 in Nepal."I think few people realize the social and biological benefits of monogamy. In fact, so-called "progressives" even believe that monogamy is "over-rated" and want to legalize polygamy, claiming that:
"Legalized polygamy in the United States is the constitutional, feminist, and sex-positive choice. More importantly, it would actually help protect, empower, and strengthen women, children, and families."
These people aren't aware that polygamy has been practiced in Asia and the Middle East for a long time, and it didn't produce the "sex-positive, child-friendly" utopia they imagine. Moreover, evolutionary psychology refutes the polygamist progressives.
In contrast to polygamy, the standard for 85 per cent of societies in the anthropological record – including the Hebrews of the Old Testament – Henrich et al. have shown that monogamy, the standard of European civilization, has enormous social benefits:
"In suppressing intrasexual competition and reducing the size of the pool of unmarried men, normative monogamy reduces crime rates, including rape, murder, assault, robbery and fraud, as well as decreasing personal abuses. By assuaging the competition for younger brides, normative monogamy decreases (i) the spousal age gap, (ii) fertility, and (iii) gender inequality. By shifting male efforts from seeking wives to paternal investment, normative monogamy increases savings, child investment and economic productivity. By increasing the relatedness within households, normative monogamy reduces intra-household conflict, leading to lower rates of child neglect, abuse, accidental death and homicide."In history, polygamous cultures always resulted in a large population of unmarried males and dramatically increases the competition between males for female mates.
"Faced with high levels of intra-sexual competition and little chance of obtaining even one long-term mate, unmarried, low-status men will heavily discount the future and more readily engage in risky status-elevating and sex-seeking behaviours. This will result in higher rates of murder, theft, rape, social disruption, kidnapping (especially of females), sexual slavery and prostitution. As a by-product, these men will probably engage in more substance abuse."Polygamy also increases intra-household conflict that results in injury to both women and children:
"Co-wife conflict is ubiquitous in polygynous households. From anthropology, a review of ethnographic data from 69 non-sororal polygynous societies from around the globe  reveals no case where co-wife relations could be described as harmonious, and no hint that women's access to the means of production had any mitigating impact on conflict. Consistent with this, an in-depth study of a fundamentalist Mormon community in the US  found substantial conflict among co-wives. "The conflict occurs because the co-wives compete for the husband's attention, and because each wife is motivated to promote the interests of her children, but to undermine the interests of the children of other wives since she has no genetic investment in those children of co-wives. Hence, any individual wife has a biological motivation to injure the children of other co-wives:
"Living in the same household with genetically unrelated adults is the single biggest risk factor for abuse, neglect and homicide of children. Stepmothers are 2.4 times more likely to kill their stepchildren  than birth mothers, and children living with an unrelated parent are between 15 and 77 times more likely to die ‘accidentally’ .Monogamy also increases the father's investment in children. Rather than competing with other males and seeking more wives, male energy is directed into increasing the success rate of the children he has with one wife. Since more males are invested in children in a monogamous culture than in a polygamous culture, they are motivated to keep a crime-free, peaceful society that protects the children they have. In a society that allows polygamy, the unmarried males do not have investment in peace or prosperity, but have a perverse motivation toward rape, crime and war because they have nothing to lose.
"Converging with these ideas is long-term research in the Caribbean, which shows how different household compositions impact cortisol levels (a stress hormone) in children. Children in nuclear families with only genetic parents showed the lowest cortisol levels. By contrast, children in households with distant relatives, stepfathers and half-siblings showed the highest cortisol levels of any household composite in the sample . This suggests that the children of polygynous households will run higher cortisol levels owing to the presence of unrelated mothers and half-siblings."
Most importantly, monogamy is the probable foundation of free societies:
"In closing, it is worth speculating that the spread of normative monogamy, which represents a form of egalitarianism, may have helped create the conditions for the emergence of democracy and political equality at all levels of government [7,91]. Within the anthropological record, there is a statistical linkage between democratic institutions and normative monogamy . Pushing this point, these authors argue that dissipating the pool of unmarried males weakens despots, as it reduces their ability to find soldiers or henchman. Reduced crime would also weaken despots' claims to be all that stands between ordinary citizens and chaos. Historically, we know that universal monogamous marriage preceded the emergence of democratic institutions in Europe, and the rise of notions of equality between the sexes (see our historical sketch in the electronic supplementary material). In Ancient Greece, we do not know which came first but we do know that Athens, for example, had both elements of monogamous marriage and of democracy. In the modern world, analyses of cross-national data reveal positive statistical relationships between the strength of normative monogamy with both democratic rights and civil liberties . In this sense, the peculiar institutions of monogamous marriage may help explain why democratic ideals and notions of equality and human rights first emerged in the West ."So "progressive" proponents of polygamy want to destroy monogamy, likely the very essential basis of a free society. They want to turn the West into a society that favors the chaotic despotism that characterizes all non-Western cultures.
They don't have a clue what they are asking for.