The term pheromone – from the Greek pherein (to carry) and hormân (excite) – was introduced in 1959 by the German biochemists Peter Karlson and Martin Lüscher, who gave it the following definition: ‘A pheromone is a substance (or a mixture of substances) which, after having been secreted by an individual (emitter), is perceived by an individual of the same species (receiver) in which it produces a specific behavioural reaction, even a physiological modification.’ Pheromones are thus chemical substances comparable to hormones; they are emitted by most animals and certain plants. They act as messages between individuals of the same species, transmitting to other organisms information which plays a role, notably in sexual attraction.