The waning power of the engagement ring

PEACOCKS strut; bowerbirds build lovenests; spiders gift-wrap flies in silk. Such courtship rituals play an important role in what Charles Darwin called sexual selection: when the female of a species bears most of the costs of reproduction, males use extravagant displays and gifts to demonstrate their “reproductive fitness” and females choose between them. For human males, shards of a crystalline form of carbon often feature. A diamond engagement ring signals a man’s taste, wealth and commitment, all to persuade a woman that he is a good bet.This particular courtship gift was dreamed up by an ad agency for De Beers, the cartel that sold almost all of the world’s diamonds throughout the 20th century. In the 1930s it started to promote a link between diamonds and marriage. Diamonds’ unmatched hardness would symbolise love’s endurance and their “fire”, or brilliance, its passion. Two months’ salary, the firm suggested, was what the ring should cost—a good investment since, as the admen said, “A diamond is forever.”