Freshly brewed coffee, rancid meat, the scent of a mother, an alarming waft of smoke—good or bad, smell is a powerful sense, capable of rousing remote memories, guiding behaviors and influencing moods. Scientists have long suspected that the immense diversity in human olfactory experience results at least partly from heredity, and now a research team has shown that the perception of specific odors can indeed be traced to one’s genes. Beyond connecting the dots between genes and odors, these findings raise intriguing questions about human evolution. Our repertoire of functional olfactory genes has been shrinking over evolutionary time—and no one knows why.