Engagement rings follow-up

A discussion with a commenter about my post on engagement rings made me realize that, in that post, I fell far short of making myself clear. Here are some clarifications.

First, I am only wondering why engagement rings are (expected to be) expensive, not why they're there at all. If the custom were to give beautiful but inexpensive rings, there would be no question to ponder. Cheap talk requires no explanation; no one wonders why we say "Thank you" and "Good morning." But when willingness to pay comes into the picture, things need explaining, because we're willing to pay only for things we value.

My commenter explains the fact that engagement rings are expensive and that only men are expected to give them by the fact that, historically, "men have always had more access to material goods, and women have traditionally been denied the ability to own them or to have sole discretion regarding their use" and that men (as opposed to women) have traditionally been taught to show how much they value things through monetary signals. However, assuming those facts are true as empirical observations (for the record, I think the first one is while the second one is not), their existence requires its own explanation: why have things historically been this particular way and not any other? Is it just an accident of history, or are there some systematic reasons behind it?

Also for the record, I think the causal narrative I've presented in my post (that expensive engagement rings are insurance for women against losing their virginity without getting anything in return) is really only a small part of the story. The big picture is biology. In strictly biological terms, female reproductive capacity is a scarce resource while male is not. To be blunt: sperm is cheap, eggs are expensive. This is why men compete over women and not the other way around. The fact that this is so, by the way, is not a social construct: in every known human culture, men compete for mates and women choose them. In our particular culture, one of the means through which men signal their "mating value" to women in this competition, are engagement rings.

Each transaction has at least two sides. I don't think that, if women (on average) didn't care one bit about the price of engagement rings, the custom of buying expensive rings would have survived this long.