First of all, while this is a 'published study' it isn't really science. They can't do tests, they can't do control groups. It's not like they can take two identical populations, except for poly/mono and then see what happens. What they are doing is all statistical analysis, none of which is listed in the study paper. And you know what they say: lies, damned lies and statistics.
Now because we're dealing with statistics you need data, which means they're using modern information. And that presents a huge problem. For today the practice of polygamy is limited to only a few religions and ethnicities; mostly those which have escaped the clutches of the empire (and so also loose many of its economic benefits). There are just too many confounding factors like race, religion, IQ, culture, politics, economics, etc. All we can do is trust the study authors correctly controlled for these. And that would be a fools errand. As it is today, scientists doing actual science, with randomized double blind controled studies of test subjects; the repeatability of those is something like 40%; which is worse than a coin flip.
Second, the study authors have a huge blind spot...
"Our goal was to understand why monogamous marriage has become standard in most developed nations in recent centuries, when most recorded cultures have practiced polygyny,"
They assume therefor that because is the dominant social system now whereas it wasn't before, it must have confired some advantage to overcome our natural poly urges, so they go looking for it (hence the study findings). But what if it was an accident of history?
There is an easy answer to their question: it piggy-backed on Christian Western Civilization like a virus; a civilization that went global with the benefit of our technology (something which historians attribute to our Christian background) or maybe some other factor (genetic, cultural, etc) that was of greater effect than monogamy. And in fact, the authors mention in the study conclusion that religions could have been a factor in it's spread. Let me further demonstrate.
What if this study was done in 1100 AD or there abouts? At that time the polygamous Vikings ruled from Scandinavia to Italy and had the European monarchies on the ropes everywhere. Furthermore the European countries were not yet stringly monogamous. At this time, if you looked around, you'd think that polygamy was the most advantageous system.
Now what if you do this study 100 years from now in the future, at a time when the polygamous Muslims have taken over the dominant world powers and polgyamy is now the norm. Again, you might think that polygamy was the most advantageous. You might look at the rise of monogamy as a temporary blip, a happenstance that occured because of the Europeans head start in technology but that eventually human biology (which the study authors admit tends to polygamy) reasserted it's natural order.
Really, what's going on here is mythmaking. They're buttressing this idea that poly leads to bad things and mono to good things. But by that measure you could look at mono marriage now and condemn it.
Counter narratives:
1. Monogamy is socialism of the sex market. Socialism never works because it violates the laws of nature. Look at today. Marriage is failing. Scientists are starting to worry about an accumulation of bad genes in our population leading to people getting sicker and sicker. Polygamy is a survival of the fittest that is necessary to ensure the biological health of our species.
2. We are advocating Biblical Marriage. Could there be bad effects to polygamy in Islamic countries that do not benefit from the Christian fruits of the Spirit? Quite obviously. But that should be different in a society ruled by Christ.
3. Even if the study authors are right, and that polgyamy leads to men without women and that leads to bad outcomes; there are other solutions besides monogamy. One that was common before monogamy is monasteries. They provide an outlet and life for unattached men that is of benefit to them and the society. They didn't go away in our culture because monogamy gave them all wives; they went away because the state found it advantageous to disband them and take their lands and wealth.
4. The study authors argument depends on showing that polygamy increases the pool of unmarried men. This would not be the case if the polygamous society had a positive birthrate and an age gap between men and women (5 years is enough). That would result in a surplus of women to ensure the rate of unmarried men did not increase. Such a setup would also result in increased family stability.
5. Monogamy is a myth; it doesn't exist. What we have is sleeping around and serial monogamy. In formally polygamous societies you often have only 10-20% of the population with multiple wives. In our monogamous society? That top % still has multiple women. Except instead of building stable families with a couple women they sleep around with multiple women leading to broken homes, broken women, and broken children. No amount of moralizing or laws will stop that. Unless you make it acceptable for them to have multiple wives. And the bottom % of men, they won't get women in any system; they're too ugly, not interested, damaged, or dead. The societal cost of all these fatherless children is massive; probably (I don't know) far greater than what the study authors found.
6. God quite clearly established polygamy with His Law, and His law was perfect, righteous and just. God would not have done that if it were not the best way. I trust God's wisdom over that of modern God hating 'scientists'.
7. Polygamy is survival of the fittest applied to the sexual market. You can't cheat nature. Nature bats last and always wins. We are biologically created for polygamy. For example, that same page
has a link to this study demonstrating that the sperm of males in a polygamous society for 12 generations were significantly more fertile than the monogamous males. What the study doesn't document is sperm health before and after nor how long it took for the effect to become evident. So it is entirely possible, but unstudied, that monogamy is leading to a steep reduction in male fertility and in far less time than 12 generations. And guess what? We're seeing this same problem in human society today with decreased sperm quality and dramatically falling testosterone levels.
And finally...
Monogamous marriage has largely preceded democracy and voting rights for women in the nations where it has been institutionalized, says Henrich, the Canadian Research Chair in Culture, Cognition and Evolution in UBC's Depts. of Psychology and Economics. By decreasing competition for younger and younger brides, monogamous marriage increases the age of first
marriage for females, decreases the spousal age gap and elevates female influence in household decisions which decreases total fertility and increases gender equality.
History isn't going to view those as virtues of monogamy. Not since it lead to subreplacement rate fertility, the gutting of all our cultural and legal institutions, and our overthrow by foreign populations.
Frankly, the fact monogamy leads to decreasing fertility is proof that it is biologically disadvantageous. Especially since it has taken us below replacement rate. It doesn't matter what your crime rate is if the species is dying.
