Let’s Talk!
Most of us try to put our best foot forward when we’re trying to attract a romantic partner. For example, we tend to wear clothes that accentuate our best physical attributes, and we engage in intelligent and witty conversations.
But what if there are other subtle factors affecting how attractive we are to the opposite sex? More specifically, what is the role of pheromones in sexual behaviour?
The word “pheromone” was introduced in 1959 by German biochemist Peter Karlson and Swiss entomologist Martin Luscher. The term pheromone comes from the Greek word pherein meaning “to transport” and hormone meaning “to stimulate.”
According to Wikipedia, a pheromone is “a secreted or excreted chemical factor that triggers a social response in members of the same species.” Therefore, a member of a particular species produces a minute amount of a chemical substance that unconsciously affects the other members of that species, but not the sender.
The concept of chemical communication between organisms is not new. Ancient Greeks mentioned that secretions from female dogs in heat attracted male dogs. Furthermore, in 1871, Charles Darwin stated in his book The Descent of Man, and Selection in Relation to Sex that mate selection included visual, auditory, and chemical signals.
There is a wide variety of pheromones that affect hormone level development and the behaviour of many plants, insects, and vertebrates. These chemical messengers can act through smell and taste or can even be ingested and directly affect certain organs, such as the brain. For example, there are alarm pheromones, food trail pheromones, and sex pheromones.
Evolution has imbued all animal phyla with the ability to produce pheromones. Some scientists affirm that in mammals these chemicals are sensed mainly by the vomeronasal organ (VNO) or Jacobson’s organ. This organ lies between the nose and the mouth (see picture above). The VNO has been identified in most amphibians, reptiles, and non-primate mammals; however, it is missing in birds, adult catarrhine monkeys, and apes.
The VNO is clearly present in the human fetus, but seems to be lacking or atrophied in adults. Three pheromone receptors have been identified in the VNO: V1Rs, V2Rs, and V3Rs. These receptors are very different from the ones found in the main olfactory (or nasal) system, therefore they may play another role.
To be effective, pheromones must be produced by organisms of minimum body size. Organisms have to be of a certain size to produce enough of these chemical factors to diffuse far into the environment to influence the members of the same species.
Consequently, bacteria are too small to use pheromones for rapid behavioural modulation such as attracting a mate. But bacteria can use pheromones to determine the population density of related organisms in the nearby area because they can slowly produce enough pheromones for this use.
There is a controversy regarding whether or not humans produce and can detect pheromones. Since these chemicals are usually found in body odor, and given that Western societies encourage good personal hygiene, it is challenging to systematically study human pheromones.
Nevertheless, there are three steroids found near the armpit (androstenone, androstenol, and androstandienone)—produced by the testes, ovaries, apocrine glands, and adrenal glands—that could be linked to pheromones. Scientists who support this theory point out that these axillary (or armpit) steroids only become active at puberty when the sex steroids affect their activity.
Moreover, German biologist Dr. Manfred Milinski is exploring the link between axillary odors and the immune system. According to Milinski, people can unconsciously gather information about the suitability of a sexual partner based on the pheromones found in these natural scents. People tend to be attracted to mates whose immune systems are healthy and different from their own.
Other studies have emerged with data that shed light on the possibility of the existence of human pheromones.
One of the best-known (and still disputed) cases supporting the presence of human pheromones is the synchronization of menstrual cycles in women (or the McClintock effect). American psychologist Martha McClintock designed a study in which a group of women were exposed to a whiff of perspiration from other women. It was found that this caused their menstrual cycles to synchronize with those of the other women.
Another intriguing case is the link between pheromones and early sexual activity. Psychologist Dr. Bruce Willis argues that in homes in which biological fathers are present, daughters tend to enter puberty and become sexually active at a later date, compared to homes in which the fathers are absent.
There are more factors affecting our mating success than our physical appearance or our wit. Nature has provided most organisms with chemical messengers such as pheromones that not only affect sexual behaviour, but also many other important activities.
Although the role of pheromones in the human population is still controversial, some behavioural studies point to the influence of these chemicals. For example, most people are sexually attracted to individuals whose smell is different from their own.
Only time will tell what other exciting discoveries researchers will make in the fascinating topic of pheromones.
Literary Truths
Here are other types of pheromones:
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- Aggregation pheromones: function by attracting a large mixed group of members of the same species at a particular location. It is usually used to protect the group from a predator or overcoming the resistance of a host by a mass attack.
- Epideictic pheromones: produced by females after they lay their eggs in an area in order to signal to other females to lay their eggs somewhere else.
- Releaser pheromones: designed to elicit a rapid change of behaviour in the recipient. Often used to attract a mate.
- Information pheromones: emitted to broadcast an organism’s identity or territory. For example, a dog may urinate in an area in order to send a message to other dogs that this territory is his.
- Primer pheromones: provoke a change in developmental events instead of behaviour in members of a species.
Truth in Motion
References
Atallah, Elias, et al. “A novel neural substrate for the transformation of olfactory inputs into motor output.” PLoS Biology 8.12 (2010).
Bennett, Richard. “A microbiologist wonders what turns us on.” Nature 461.7260 (2009): 15.
Pearson, Helen. “Mouse data hint at human pheromones.” Nature 442.7102 (2006): 495.
Stansfield, William D. “Science & the senses: perceptions & deceptions.” The American Biology Teacher 74.3 (2012): 145.
“What the nose knows.” The Gay & Lesbian Review Worldwide 12.4 (2005): 10.
Wyatt, Tristram D. “Fifty years of pheromones: powerful chemical signals have been identified in moths, elephants, and fish, recounts Tristram D. Wyatt. But, contrary to stories in the popular press, the race is still on to capture human scents.” Nature 457.7227 (2009): 262.
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