When the term “pheromone” was defined in the late 1950s by insect researchers Peter Karlson and Martin Lüscher, it carried three main implications: that it was a message to which only members of the same species would respond; that it was a single, identifiable chemical; and that it had a definite behavioral or physiological effect on the recipient.
That definition has not held up well over time. Even in insects, each of the criteria has been violated by substances that most researchers are still willing to call pheromones. For vertebrates, the definition has been progressively loosened to the point that researchers are now heatedly debating the meaning of the term. Scientists now suggest there are four kinds of human pheromones–primers, releasers, modulators and “signalers” that provide information to the recipient without directly altering behavior. (more…)