If we’re talking about the animal kingdom POV, then an expensive diamond is physical proof of the male’s resourcefulness and ability to provide for young. I would argue that if the diamond was displaced as this proof then it would shift to another physical object that’s publicly displayed such as a house or car.

I agree, but at the same time, we're much more intelligent than penguins, so it's a shame that we also signal commitment with a fancy rock. Something like a work of art or rare book would serve the same purpose but would have more personal meaning.

I wanted to say you've committed the naturalistic fallacy, but actually, you've also misrepresented the meaning of mating behaviors in essential ways and made a few tacit and unwarranted jumps in between.

Humans are rational animals. Yes, obviously we have natural inclinations (they aren't irrational, btw; they have a purpose and only when the inclination is disordered, deficient, excessive, or we behave in ways opposed to the good when moved by the inclination can we speak of irrationality). However, we can make errors in judgement when interpreting signs and relating these signs to our inclinations. Marketing is often actively engaged in confusing people when it comes to what things mean. And when we get the meanings of signs wrong, we relate things erroneously to our natural inclinations. So this very recent practice of buying extravagant diamond rings beyond our means is the product of psychological manipulation and deceit that exploits vice and inclination by effectively lying about what an overpriced diamond ring signals.

It would be an error to assume that a woman from a culture that values thrift would react positively to such a gift, much less demand it. She might be left thinking that the man is financially irresponsible. Most cultures do not make spending obscene amounts of money on a ring a common practice. The engagement ring has historically been a symbolic gesture, not a demonstration of irresponsibility, immodesty, profligacy, and vanity.

In the case of peacocks, they ARE their plumage. Their plumage is not a sign of seriousness, but a sign of fitness and health and shaped by inherent traits and female selection (her interpretation or recognition that the better the plumage, the better the health), not male initiative. The peacock also isn't willing his plumage.

You can just as easily construe the ring as a test of your potential wife's character. If she refuses to marry you because you haven't spent a fourth or more of your salary on a ring, then good riddance. Who wants to be saddled with a fraudulent, vain, and vapid creature like that. She would make a terrible mother.

In many cultures, marriage was traditionally a more convoluted affair, involving both families and there's a strong preference to marriage with a family that your family knows and trusts. The socio-economic status of prospective mates and their families are considered. There's a solemn ritual in a religious setting where all members of the community are invited to witness an oath. And thus the expensive shiny thing isn't _as_ necessary, although often expensive gifts are exchanged anyway.

These days people get married with somebody they met on Tinder for a month because "true love". The weight of a promise from a person you met for a couple weeks and from a family you've known for decades is different, which accounts for the modern inventions you despise as compensation.

I mean, I'm not saying this expensive ring thing is a desirable game to play, and I don't disagree that there are vain people out there, but the ring serves a particular purpose in the mating game of modern society, not just to satisfy some people's vanity.

(btw, if you think about it, an engagement ring isn't inherently that great for showing off. Most people put it away in a little box and wear a less conspicuous ring anyway.)

Different cultures uses different displays to convey status. In cultures which do not place similar importance on a diamond ring, they may place equal importance on other displays, such as a large wedding banquet or purchase of a residence. Regardless of the specific expression of status in various cultures, I would think that they exist as a constant across all cultures.