For hundreds of years,scientists have known that organisms, and humans in particular, secrete avariety of substances, in which many of them are classified as what are calledpheromones. Pheromones, as defined by Dictionary.com, are “a chemical substanceproduced and released into the environment by an animal, especially a mammal oran insect, affecting the behavior or physiology of others of its species.”There are different classifications of pheromones, in which they each initiatea specific response, such as sex pheromones. Sex pheromones are released bymany species of animals in order to attract mates, but whether or not humansrelease them has been a topic of scientific debate. By reviewing the chemicalcomposition of a pheromone and its properties, how pheromones are analyzed, andthe evolutionary adaptions the body has undergone, it is apparent that the bodydoes not produce sex pheromones, nor do we have the capability of sensing them.Due to their molecularstructure, pheromones fall under the category of what are known as steroids.
Steroidsare classified as molecules consisting of 17 carbons arranged in a series offour rings, in which they can be either natural, secreted from endocrineglands, or man-made. Most steroids are named based off of their source or physiologicalfunction. Due to the consistent four-ringed structure throughout all steroids, theproperties of the steroids are determined by the functional groups attached andtheir configurations. In order to thoroughly analyzesteroids, they must be isolated from a natural source. Therefore, extractionmust be used, where the steroid is easily dissolved within the aqueous fluid. Thesource material is initially dehydrated using an alcohol solvent, where theproteins correlating with the steroid are denatured and the steroids are dissolved.Turning the tissues or extracted substances into soap through alcohol splitsmolecules within an ester or triglyceride and allows for the extraction ofthese molecules through solvents that are water-immiscible, such as ether orhexane.
In order to purify these extractions, methods such as recrystallizationare used. A number of molecular methodsare used to analyze steroids, such as nuclear magnetic resonance imaging,infrared spectroscopy, mass spectroscopy, and X-ray crystallography, but moststeroid analysis involves chromatography. Steroids tend to behave in a veryspecific way in selective chromatographic situations, therefore, making it easyto identify what steroid is being analyzed. The identification comes from examiningthe components of the steroid to see what derivatives they convert to.Thin-layer, paper, liquid, and gas-liquid chromatography show the specificfeatures of the compound that determine the properties and function of thesteroid, where the liquid and gas-liquid chromatograph correlate to the massspectrometer and allow the fragmentation patterns to be observed simultaneously.
When performing total steroidsynthesis, a monocyclic starting material is typically used, such as quinone.The other rings are attached through a series of condensation reactions, wherea molecule, such as water, is eliminated with the help of a catalyst. Smallermolecules must be used in the condensations in order to obtain the correctstereochemistry and for proper fusion of the rings. When a new ring is closed,functional groups must be present in order to attach more rings. However, inmost labs, partial synthesis takes place, where scientists work to modifypreexisting steroids. This involves starting with a structure that can easilybe manipulated into the desired product.
Based off of a number of experimentsinvolving molecular analysis, some scientists have arrived to the conclusionthat the steroids commonly known as androstadeinone, androstanol, andandrostenone could be classified as human pheromones. Androstadienone is anendogenous steroid, meaning that it originates from a cell, tissue, ororganism, and it is often put into men’s products, as it claims to increase sexualattraction, but no convincing evidence has been published to confirm this. Androstanolis also endogenous and is commonly found in the saliva of pigs, but it hasnever been found to have a definite function within the human body and it is justassumed to be a pheromone. The third steroid, androstenone, is classified asthe first mammalian pheromone to be identified, where it is also most commonlyfound in pig’s saliva. Reporters say that when a pig has high concentrations ofthis steroid within the saliva, females in heat are more likely to take placein the mating stance. This steroid is often put in products that are sold topig farmers in order to test sows and determine the correct time toartificially inseminate.
However, there is also no sound evidence to supportthis claim. There are a variety of reasons why manyscientists believe that these three compounds are classified as pheromones,beginning with the fact that they are steroids that fall under the category ofexcreted hormones and are commonly present within urine, axillary sweat glands,salivary glands, and semen. This implies that they could be transferred fromone organism to another. These excretions tend to smell like urine or must-like,if they are even sensed, reiterating the idea that they originated from animalsand are released for social attractions. Furthermore, females tend to be moresensitive to them and produce a lower concentration in comparison to males,indicating sexual dimorphism, and they can be used to differentiate betweensexes.
However, there are a number of problems with these arguments. In an experiment performed, usingcapillary gas chromatography and mass spectrometry, it was proven that out of24 males, only 10 of the males had androstenone in their axillary hair; it wasnot identified in any other secreted fluid. Although these three substances arefound in bodily fluids and secretions, they are also found in most plant species,portraying that they most likely don’t have a social or sexual significance. Anumber of people cannot smell these substances unless they are present in verylarge amounts, and even when they do smell them, most people report that theyfind these smells unpleasant. Assuming that the olfactory sensory system isinvolved in the detection of pheromones, not one of the three steroids providemuch of anything to the next generation of normal body odor that come from avariety of C6-C11, typical unsaturated acids. Inaddition, in order to determine the gender of another being is dependent onodors that derive from the axilla or breath, and that is all dependent on howstrong or pleasant the scent is versus its chemical composition.
Lastly, sincepheromones are supposed to be specific to a species, it is unlikely that thepheromones present in pigs have the same effect in humans.Analyzing the molecules in sensorysystems has proved to be more beneficial and informative, rather than attemptingto measure the function, which can be quite challenging. This appears to be thecase in the instance of pheromone detection in species that are vertebrates. Thevomeronasal organ, also known as the VNO, is the preliminary step of theolfactory system and is the main detection site of pheromones. In some species,such as mice, the VNO is depicted as a pair of tube like structures that can befound underneath the nasal cavity. However, in humans, it is a small openingwithin the nasal cavity.
The VNO recognizes chemical stimuli by their molecularbonding to what is known as G-protein-coupled receptors, also known as GPCR’s. TheVNO in rodents reveals two kinds of GPCR’s that have been designated as primarypheromone receptors, known as V1Rs and V2Rs. The V1R’s are stimulated byhydrophobic molecules that bind to the GPCR’s and the V2R’s by peptides. Within the V1R receptor, it has beenobserved that the deletion of a chain of sixteen receptors causes females tobecome more aggressive and the males change their sexual behavior.
The neuronsthat are present within the VNO system have a specific ion channel, known as TRPC2,that is triggered by co-expressive secondary messengers that are downstream ofthe two receptors. When TRPC2 is not present, the pheromone-mediated aggressionbetween male mice is not present, indicating that the TRPC2 channel isnecessary in order for the VNO to function normally. In addition, whenapproached by a castrated male, the males with the missing TRPC2 channel willattempt to mate at approximately the same prevalence as that with female mice,indicating that the VNO also correlates to gender identification. Theidentification and analysis of the chemical components present within a VNO signaltransduction, using molecular methods, allows for the determination of whetheror not a species has a fully functioning VNO. It was determined that the VNO inhumans is vestigial. The TRPC2 gene present in humans has evolved to where ithas four nonsense mutations, two deletion/insertion mutations, and the majorityof the V1R’s are composed of pseudogenes. By analyzing the genes in extinct andpast species, it was determined that the VNO started to mutate about 25 to 40million years back. By calculating a non-synonymous to synonymous mutation ratealong components of primate phylogeny, it was confirmed that the selectionpressure became more relaxed around that time.
This confirmed that the V1Rreceptor genes underwent relaxed pressure; therefore, the number of pseudogenesincreased showing the presence of four genes but the functionality of them hasnot been determined. However, it has been determined that the four genes werenot conserved within the chimp species. In addition, most olfactory sensoryneurons present within an organism are bipolar cells. These neurons arereplaced about every 90 days and express a specific olfactory receptor. These receptorsallow the system to be specific for certain molecules but persistent for othermolecules. In mice, 16 olfactory receptor genes select for isovaleric acid, butin humans, the same gene cluster was unable to be found.
This piece of evidenceportrays that humans do not have the receptors specific for isovaleric acid. Theresults from these series of tests show that the vomeronasal transductioncomponents became absent about 25 to 40 million years ago. However, the loss ofthis transduction occurred in the same time frame that trichromacy appeared,also known as color vision, portraying that perhaps pheromone signaling wasreplaced with visual signaling.
After going over the structure of the assumedpheromones and some of their analytical characteristics along with theevolutionary adaptions the body has undergone throughout time, it is unlikelythat the human body actually possesses the ability to product pheromones oreven sense them. Although pheromones are steroids that are naturally madewithin the human body’s glands, there is not enough concrete evidence on thesesecretions to prove that they induce sexual drive. As science is always advancingand changing, there is always the possibility that someone will prove thistheory wrong someday, but as of this point in time, your nose will not be ableto help you find your soulmate.