Many organisms including insects, amphibians and yeasts use sex pheromones for attracting individuals of the opposite sex, but what happens to sex pheromones as new species emerge? New research publishing January 22 in the open-access journal PLOS Biology from Taisuke Seike and Hironori Niki at the National Institute of Genetics, Japan and Chikashi Shimoda at Osaka City University, Japan studies sex pheromones in the fission yeast Schizosaccharomyces pombe, revealing an “asymmetric” pheromone recognition system in which one pheromone operates extremely stringently whereas the other pheromone is free to undergo a certain degree of diversification, perhaps leading to a first step towards speciation.