Gorillas are monogamous and have small genitals, chimps are highly promiscuous and have big genitals, humans are somewhere in between.
Actually, I read that human (males) have the biggest genitalia of any primate, both in absolute size & relative to body mass. I have no source for this, sorry.
So.... the idea would be to have random morals for each civilization regarding this?
I think randomized ethics for civs is definitely the best way to go, and would explain a lot of the things we've seen so far. For example, right now all dwarf cultures have the same moral code, including [TORTURE_FOR_INFORMATION:PUNISH_CAPITAL]. So why do some dwarven civilizations have a
god of torture? Which, theoretically, could be the most popular deity, openly worshiped by the rich & poor alike? The most likely solution seems to be to give each civilization a set of ethics that agrees with its already-randomized gods, or alternatively to randomize the culture's moral code, and then base the pantheon off
that.
As I said earlier:
Each civilization would have these same traits, randomized at worldgen: One for that civ's acceptance of citizens engaging in free love, and another for that civ's understanding of homosexual relationships. (Each civ's Promiscuity must be kept above a certain minimum, and Homosexuality below a certain maximum, or the whole civilization would likely die out in just a generation or two.) As each child is born, his stats in these traits are modified (to some degree) by the culture into which he was born--he will be expected to conform to society's standards, leading him to possibly feel confined by constrictive rules, and/or disgusted by the depraved antics of others.
Also of interest is the dynamic of dwarves moving from one civilization to another, and possibly to another. Each dwarf's "true" values of Promiscuity and Sexuality would be paramount, but his
behavior would likely be strongly pressured by the expectations of his society. As he migrates from one home to another, each culture would successively modify the dwarf's expressed desires; but each successive civilization would have
less effect on his behavior than the previous one, to reflect the dwarf's becoming a bit more worldly, jaded, and aware that he can essentially pick & choose a culture that can suit
him. This would lead to migrant dwarves acting in ways to which they had become accustomed in their previous forts: "She is a former member of the Tentacle of Sacks" and "He is a former member of the Cloistered Abbey" might not turn out to have a lot in common with each other,
or with the social mores of your own fort.