The root problem is that, via the magic of bad science reporting, the
actual source isn't
actually talking about polygamy. It's
specifically talking about
polygyny, systems where one man has multiple wives;
http://rstb.royalsocietypublishing.o...9/657.full.pdf
They're specifically talking about practices that create a pool of unmarried males without real prospects. But this
also isn't comparable to modern society, which
is culturally monogamous, and using this study as an argument regarding modern society just does not work as a result.
They're also pretty darned free about drawing the loosest of correlations, like suggesting that monogamous marriage leads to equality of the sexes, even though in the case of Christian Europe, we're talking about a lead time of, oh, at least 1500 years or so, minimum. They don't have a ton of data so I can't fault them for raising the question, and they admit that it's a really flimsy connection at best, but that seems to be lost in translation between their study and the reporting you're quoting from.