Also, this seems to make no mention of 'rearing complexity'. A more developmentally complex brain should imply prolonged rearing and have a bias of survival in favor of shared parenting.
I guess you can find anything you're looking for in gene expressions, if you really want.
Primates are significantly brainier than most of the rest of Mammalia, on average, and humans and gibbons are the only primates that are more monogamous than polygamous. Cetaceans and elephants also have comparatively large brains and aren’t monogamous.
Extraordinary claims require extraordinary proof. Got any citation for that?
If humans were monogamous as you suggest, the figure of male reproduction would be far closer to 100%. But we’re not. We’re polygynous — a harem-based species. And the 40% figure you just cited proves that: Less than half of the men mate with all of the women. That’s not called monogamy dude. That is called polygyny.
The sexual part seems pretty familiar from looking around current society, and the children support part isn't far off from now either.