air. These pheromones attract receptive sows, causing it to adopt a specific mating posture, known as standing, which allows the male boar to mount it and therefore copulate. Species specificity Regardless of the species, sex pheromones are often structurally similar and for that reason different species need to be able to respond to the correct pheromone. It is the variation in the ratios of each compound within a pheromone that yields species specificity. The use of mixtures of compounds as pheromones is well documented in insects, research into male orchid bees demonstrates that specific odours mediate exclusive attraction within a species. See also Fluctuating asymmetry Major histocompatibility complex and sexual selection Sexual attraction Sexual motivation and hormones Ovulatory shift hypothesis References Sexual attraction Physical attractiveness Body odor