by Patrick Appel
Conor opposes diamond engagement rings, calling them "the ultimate sucker's purchase." I've advocated this same position in the past, but here's a passage, from Paul Bloom's excellent How Pleasure Works, that made me think twice:
[Psychologist Geoffrey Miller's first insight about costly signaling is the idea] that displays of personal quality are only taken seriously if they involve some cost, some level of difficulty or sacrifice. If anyone can easily do the display, then it is worthless, because it is trivially easy to fake. Costly signaling shows up in the gifts we give to one another, particularly during courtship. Miller asks, rhetorically, "Why should a man give a woman a useless diamond, when he could buy her a nice big potato, which she could at least eat?" His answer is that the expense and uselessness of the gift is its very point. A diamond is understood as a sign of love in a way a potato isn't, because most people would only give on to someone they care about, and so the giving signal some combination of wealth and commitment.
This argument is unlikely to convince those dead-set against diamond engagement rings, but given that some sort of costly signaling is unavoidable when proposing marriage, I'd be curious to hear about other actions or gifts that would as effectively signal commitment. Keep in mind this subsequent paragraph when making suggestions:
Financial value is not the only signal of commitment. The economist Tyler Cowen points out that the best gifts for someone you live with are those that you, yourself, wouldn't want. He points out that even if his wife would enjoy the complete DVD set of Battlestar Galactica, it would be a lousy gift, because he would also get pleasure from it, and so the giving doesn't signal any particular love for her.
Most expensive objects (cars, houses, flat-screen TVs) wouldn't work very well as engagement gifts because the giver would receive equal benefit. Diamonds are typically only desired by women, which, using Cowen's formula, makes them excellent engagement gifts for women.