In my opinion, all forms of sexuality are natural. I mean, what's the alternative, them being artificial?
In comparison, no cars or pairs of glasses or computers are natural. Doesn't mean I'm going to stop using them.
Good point about how you can pass things through females. I think then I would add a lack of consideration for women. In a lot of societies, they had few rights, and using them to pass property might have felt like giving them too much importance.
I was reading the Amicus's closing arguments for the current BC polygamy case. One part I found interesting was a quote about how monogamy advantages men from a Darwinian point of view.
The basis was that, survival-wise, it's best for men to have as many mates as possible, and for women to have mates who can support the children they have. Therefore the Darwinian point of views sees these as the goals, and nothing about love, freedom, jealousy or anything like that.
From a Darwinian point of view, with polygamy women have the option to marry rich men. If they're already married, no problem, and they can support several wives. From that point of view, it's better for them than monogamy, in which men get "taken", and women have to marry men who are poorer.
Polygamy results in rich men having many wives, poor men having none. (Notice this is focusing on polygyny. I believe it's because it's also a study on patriarchal societies).
So, polygyny is better for all women (they all get to pick a mate who can support their kid better compared to who they could with monogamy) as well as for some men. But it's bad for some other men.
Therefore, the quote mentions how monogamy becomes a compromise between rich men and poor men. Rich men keep having first pick in mates, but have to limit themselves to one at a time. Poor men get to have wives that "trickle down" due to not being able to marry already married rich men. Women end up, on average, poorer and less supported, as do their children.
It was an interesting take, as people are quick to talk about how polygyny is bad for women. I thought a study about how monogamy might have been put in place to advantage men was definitely an interesting read.