The Big [Censored] Theory

> I don't think there are any sensible "defaults" for human cultures

There are loads of sensible "defaults" for human cultures. Aversion and disgust at the practices of unfamiliar out-groups is one - keeps us from getting their diseases. Practices assuring paternity are another - males that are indifferent to who's children they raise aren't very well selected for. Risk aversion in, and preference for protection of, child-bearing females by the group is a third - harm to these females disproportionately affects the ability of the group to reproduce and pass its genes. There are many, many others, and we have many of them in common with our animal relatives.

I'd agree with those (I just don't necessarily think of them as "defaults", which implies there's no real disadvantage to adopting alternative shared cultural understandings). And I'd suggest that an aversion to talking about sex is surely the opposite of a practice assuring paternity?

Well, it's complicated, but I'd agree with a below poster that it seems like the "implementation" of these practices tends towards limiting opportunities for females to mate outside of their designated partners. This includes:

1. Physically isolating females from males.

2. Conditioning females so they won't seek these opportunities.

In combination, these factors seem to taboo any discussion of sex at all in mixed male/female company. It seems our standards for what is "family friendly" grows out of these taboos. You'll notice that in exclusively male company discussing sex is generally much less taboo.

With the obviously problematic morality aside, this does seem like the most effective approach to assuring paternity, particularly in small, low-tech, tribal groups.

Edit: There's also the need to limit sexual violence, which also seems to be a factor in tabooing discussion of sex in mixed company.

Why would something being a default imply that there is no real disadvantage to adopting the alternative position? Taking other examples, if the default is for women to have sex with only a single man, why is it implied that there are no disadvantages to women having sex with many men? At least in the way I think of defaults, the value of the default vs the alternative is an entirely different variable.

It was arguably a poor choice of word. If a particular behaviour obviously has a significant selective advantage (at a cultural level) and becomes predominant it's done so on that basis. Whereas I'd think of a "default" as what would arise if you tried to start a new culture from scratch with a group of unconnected individuals with no exposure to other cultural ideas. The only defaults I'd expect to see are those driven by our biological makeup, e.g. we'd come up with a shared language that had certain basic properties, we'd adopt some sort of method of pair-bonding, we'd probably continue to have sex in private, and so forth, but to the level of specific taboos (whether it's discussion of sex, eating particular foods, wearing particular clothing etc.), I'm less convinced it makes sense to talk about defaults.