The purpose of the diamond ritual is to require the male (or whoever) to put his money where his mouth is, to prove that he is sincere about the relationship. And what's the old saying? "Money has a truthfulness. If a man speaks of his honor, make him pay in cash."

The diamond is idea for this purpose because it has almost no resale value. It's a way for the male to make a demonstratively extravagant purchase, one which the female (or whoever) is not able to whip back around for a cash refund.

Of course, it didn't have to be diamonds. Were it not for the DeBeers' marketing savvy, any arbitrary rare object could've sufficed. If technology had evolved differently, women might now be wearing tiny LCD displays on their fingers which play a video loop of their husbands throwing a bundle of cash into the ocean.


http://science.slashdot.org/comments.pl?sid=202746&cid=16588542