Pheromones (from the Greek pherein meaning to transport and hormone meaning to stimulate) are small chemicals that are released by the body that signal a message to other individuals of the same species. They have been well documented as a communication method between many species of insects and even within prokaryotic organisms. The subject of whether humans use pheromones as a method of communication is of large interest to the scientific community and is currently being researched. Some evidence points to this being true—some pheromones are used and can alter human physiology. The vomernasal organ (VNO), thought to be a vestigial organ (an organ that remains but no longer plays a role in the species as it evolves), has been associated with the reception of pheromones. One point of evidence in favor of pheromones being a mode of communication among humans is the synchronization of female menstrual cycles.
Types of Pheromones
Many species use pheromones as a form of communication between individuals of that species. As such, these pheromones can convey a multitude of information based on their chemical composition. Pheromones are classified by the signal that they provide and their chemical composition. These include two main categories of pheromones: releaser pheromones and primer pheromones. Releaser pheromones are responsible for an immediate response in the organism that is receiving the signal. There are three main types of releaser pheromones: sex pheromones, alarm pheromones, and recruitment pheromones. On the other hand, primer pheromones create a physiological change that will then result in a behavioral response. One example of this is the release of gonadotropin-releasing hormone that will elicit mating behaviors in female rats called lordosis (this helps to attract male rats in order to mate).
Sex pheromones are one of the most widely known pheromones. These chemicals typically indicate that a specific individual is ready for breeding, especially females. In many species, the female is only prepared to copulate when she is ovulating. Pheromones help to identify those ovulating females so that males of that species can fertilize offspring. Additionally, males will release sex pheromones particularly to convey information about their genotypes so that females can select a mate. Some sex pheromones will suppress reproductive behavior of the same sex so as to create a monopoly on resources (the other sex of the species). These pheromones are also the mostly widely studied in humans with varied conclusions. Overall, it appears that far too many things are going into the human olfactory system to concretely state that pheromones play a definitive role in human sex behaviors.
Alarm pheromones play a role in a synchronized response to predators. These pheromones are volatile compounds that typically trigger either aggression or fear in members of the same species. This helps to preserve the species as other members are aware of the danger. Aggregation pheromones are responsible for driving the species to one physical location. Typically, the males of the species are the ones that release this pheromone, which is attractive to both males and females of the species. This form of pheromone is beneficial for the species as it helps with the synchronization of attack by the same species. It also plays a role in reproduction by attracting many potential mates to the same location.
Pheromones and the Menstrual Cycle
One of the first and largest studies in favor of pheromones being utilized by humans is a study performed demonstrating the effects of male and female pheromones (male and female sex-specific hormone precursors) on the female menstrual cycle. It is well documented that the menstrual cycles of women who spend a large amount of time together become synchronized. This is sometimes referred to as the McClintock effect. It is suggested that female pheromones influence other females to lengthen or shorten parts of the menstrual cycle until synchronization is achieved. Male hormones have also been demonstrated to alter female cycles by decreasing fertility issues as well as regulating the menstrual cycle by altering the length of each portion of the cycle. Unfortunately, this evidence is not entirely convincing as there are many other factors affecting the female cycle including sleep, stress, and other behavioral patterns.
Within most species that utilize pheromones to communicate, the vomeronasal organ is the sensory organ responsible for the detection of pheromones. It plays a large role in reproductive behaviors and other social behaviors in part by the responses generated to pheromones. In humans it is largely regarded as a vestigial organ, or an organ that is “extra” and does not serve an obvious purpose. However, this is not completely accepted and some research is demonstrating that it might play a role in human pheromone reception, integration, and response.
Riannon C. Atwater
See also: Olfactory System; Vomeronasal Organ
Doty, Richard L. (2014). Chapter 19: Human pheromones. In C. Mucignat-Caretta (Ed.), Neurobiology of chemical communication. Boca Raton, FL: CRC Press/Taylor & Francis. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK200980/
Human pheromones. Retrieved from http://www.macalester.edu/academics/psychology/whathap/ubnrp/pheromone10/human%20pheromones.html