What are Pheromones?
Pheromones can be a variety of substances, which are secreted by many different animal species and alter the behavior of individuals of the same species. Some examples of pheromones include chemicals that can tell another animal if the animal is in the mood to mate or in distress, or if the animal is preparing to attack or retreat in fear. (Sociobiology: The Abridged Edition, 1980, 113)
According to E.O. Wilson in Sociobiology, it is believed that pheromones were the first signals used to communicate between the earliest forms of life. All communication between ancestral procaryotes was chemical and was probably passed on to eucaryotic protozoans and so on. It is also believed that pheromones are the precursors to hormones. Today, pheromones remain the fundamental signals for most organisms and chemical communication remains virtually universal among all living organisms. (Sociobiology: The Abridged Edition, 1980, 113)
According to an article in Bioscience magazine, there are two basic types of pheromones. "Releaser" pheromones are pheromones that evoke a rapid response in the animal and "primer" pheromones cause a more delayed response, such as the menstrual cycle mentioned below. ("Pheromones: what's in a name?", Bioscience, 1998, 48:505-11)
There are also two other terms that are used to describe chemicals that are very similar to pheromones, except they are used to communicate between similar species, not just within a single species. The first term is "allomone". Allomones are chemicals which are adaptive to the sender. "Kairomones", however, are adaptive to the receiver. However, it has been difficult for scientists to differ between the two terms, so allomone has been the more commonly used one. (Sociobiology: The Abridged Edition, 1980, 113)
General Overviewl of Chemical Signals and Some Examples
Figure from Insect Pheromones and Their Use in Pest Management, 1998, 5
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