The waning power of the engagement ring

(The Economist) - 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. Greater equality for women might seem to render male-courtship displays redundant. But mating preferences evolved over millennia and will not change quickly. If diamonds were to cease being a way to signal a man’s marriageability, what might take their place?