The global economic and environmental crises show that conspicuous consumption is a key problem in the 21st century. The new science of evolutionary psychology offers some unique insights into the origins and nature of runaway consumerism. In this talk I'll explore how conspicuous consumption arises from human instincts for showing off our intelligence, personality traits, and moral virtues to family, friends, and mates. Consumerism is not a matter of 'materialism', but of runaway signalling, status display, and socially validated narcissism. This new perspective explains some otherwise baffling aspects of consumer behaviour, product design, branding, and marketing, such as why economic growth does not much increase human happiness. It also suggests some practical policy changes that could reduce consumerism's personal and ecological costs, and that could increase its social and cultural benefits.