Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Olfaction is the sense of smell. It is mediated by specialized sensory cells of the nasal cavity of vertebrates, and by sensory cells of the antennae of invertebrates. Most mammals and reptiles have two distinct olfactory systems which are the main olfactory system, and the accessory olfactory system - principally used to detect pheromones. Research suggests that humans can subconsciously tell if a potential mate will pass on favorable traits to their offspring through scent. According to research on human mating, the effect of scent on males and females differs and part of this difference is caused by the different motives each gender holds for mating...