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For hundreds of years,
scientists have known that organisms, and humans in particular, secrete a
variety of substances, in which many of them are classified as what are called
pheromones. Pheromones, as defined by Dictionary.com, are “a chemical substance
produced and released into the environment by an animal, especially a mammal or
an insect, affecting the behavior or physiology of others of its species.”
There are different classifications of pheromones, in which they each initiate
a specific response, such as sex pheromones. Sex pheromones are released by
many species of animals in order to attract mates, but whether or not humans
release them has been a topic of scientific debate. By reviewing the chemical
composition of a pheromone and its properties, how pheromones are analyzed, and
the evolutionary adaptions the body has undergone, it is apparent that the body
does not produce sex pheromones, nor do we have the capability of sensing them.

Due to their molecular
structure, pheromones fall under the category of what are known as steroids. Steroids
are classified as molecules consisting of 17 carbons arranged in a series of
four rings, in which they can be either natural, secreted from endocrine
glands, or man-made. Most steroids are named based off of their source or physiological
function. Due to the consistent four-ringed structure throughout all steroids, the
properties of the steroids are determined by the functional groups attached and
their configurations.

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In order to thoroughly analyze
steroids, they must be isolated from a natural source. Therefore, extraction
must be used, where the steroid is easily dissolved within the aqueous fluid. The
source material is initially dehydrated using an alcohol solvent, where the
proteins correlating with the steroid are denatured and the steroids are dissolved.

Turning the tissues or extracted substances into soap through alcohol splits
molecules within an ester or triglyceride and allows for the extraction of
these molecules through solvents that are water-immiscible, such as ether or
hexane. In order to purify these extractions, methods such as recrystallization
are used.

A number of molecular methods
are used to analyze steroids, such as nuclear magnetic resonance imaging,
infrared spectroscopy, mass spectroscopy, and X-ray crystallography, but most
steroid analysis involves chromatography. Steroids tend to behave in a very
specific way in selective chromatographic situations, therefore, making it easy
to identify what steroid is being analyzed. The identification comes from examining
the components of the steroid to see what derivatives they convert to.

Thin-layer, paper, liquid, and gas-liquid chromatography show the specific
features of the compound that determine the properties and function of the
steroid, where the liquid and gas-liquid chromatograph correlate to the mass
spectrometer and allow the fragmentation patterns to be observed simultaneously.

When performing total steroid
synthesis, a monocyclic starting material is typically used, such as quinone.

The other rings are attached through a series of condensation reactions, where
a molecule, such as water, is eliminated with the help of a catalyst. Smaller
molecules must be used in the condensations in order to obtain the correct
stereochemistry 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, in
most labs, partial synthesis takes place, where scientists work to modify
preexisting steroids. This involves starting with a structure that can easily
be manipulated into the desired product.

Based off of a number of experiments
involving molecular analysis, some scientists have arrived to the conclusion
that the steroids commonly known as androstadeinone, androstanol, and
androstenone could be classified as human pheromones. Androstadienone is an
endogenous steroid, meaning that it originates from a cell, tissue, or
organism, and it is often put into men’s products, as it claims to increase sexual
attraction, but no convincing evidence has been published to confirm this. Androstanol
is also endogenous and is commonly found in the saliva of pigs, but it has
never been found to have a definite function within the human body and it is just
assumed to be a pheromone. The third steroid, androstenone, is classified as
the first mammalian pheromone to be identified, where it is also most commonly
found in pig’s saliva. Reporters say that when a pig has high concentrations of
this steroid within the saliva, females in heat are more likely to take place
in the mating stance. This steroid is often put in products that are sold to
pig farmers in order to test sows and determine the correct time to
artificially inseminate. However, there is also no sound evidence to support
this claim.

There are a variety of reasons why many
scientists believe that these three compounds are classified as pheromones,
beginning with the fact that they are steroids that fall under the category of
excreted hormones and are commonly present within urine, axillary sweat glands,
salivary glands, and semen. This implies that they could be transferred from
one 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 animals
and are released for social attractions. Furthermore, females tend to be more
sensitive to them and produce a lower concentration in comparison to males,
indicating sexual dimorphism, and they can be used to differentiate between
sexes. However, there are a number of problems with these arguments.

In an experiment performed, using
capillary gas chromatography and mass spectrometry, it was proven that out of
24 males, only 10 of the males had androstenone in their axillary hair; it was
not identified in any other secreted fluid. Although these three substances are
found 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. A
number of people cannot smell these substances unless they are present in very
large amounts, and even when they do smell them, most people report that they
find these smells unpleasant. Assuming that the olfactory sensory system is
involved in the detection of pheromones, not one of the three steroids provide
much of anything to the next generation of normal body odor that come from a
variety of C6-C11, typical unsaturated acids. In
addition, in order to determine the gender of another being is dependent on
odors that derive from the axilla or breath, and that is all dependent on how
strong or pleasant the scent is versus its chemical composition. Lastly, since
pheromones are supposed to be specific to a species, it is unlikely that the
pheromones present in pigs have the same effect in humans.

Analyzing the molecules in sensory
systems has proved to be more beneficial and informative, rather than attempting
to measure the function, which can be quite challenging. This appears to be the
case in the instance of pheromone detection in species that are vertebrates. The
vomeronasal organ, also known as the VNO, is the preliminary step of the
olfactory 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 be
found underneath the nasal cavity. However, in humans, it is a small opening
within the nasal cavity. The VNO recognizes chemical stimuli by their molecular
bonding to what is known as G-protein-coupled receptors, also known as GPCR’s. The
VNO in rodents reveals two kinds of GPCR’s that have been designated as primary
pheromone receptors, known as V1Rs and V2Rs. The V1R’s are stimulated by
hydrophobic molecules that bind to the GPCR’s and the V2R’s by peptides.

Within the V1R receptor, it has been
observed that the deletion of a chain of sixteen receptors causes females to
become more aggressive and the males change their sexual behavior. The neurons
that 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 of
the two receptors. When TRPC2 is not present, the pheromone-mediated aggression
between male mice is not present, indicating that the TRPC2 channel is
necessary in order for the VNO to function normally. In addition, when
approached by a castrated male, the males with the missing TRPC2 channel will
attempt to mate at approximately the same prevalence as that with female mice,
indicating that the VNO also correlates to gender identification. The
identification and analysis of the chemical components present within a VNO signal
transduction, using molecular methods, allows for the determination of whether
or not a species has a fully functioning VNO. It was determined that the VNO in
humans is vestigial. The TRPC2 gene present in humans has evolved to where it
has four nonsense mutations, two deletion/insertion mutations, and the majority
of the V1R’s are composed of pseudogenes. By analyzing the genes in extinct and
past species, it was determined that the VNO started to mutate about 25 to 40
million years back. By calculating a non-synonymous to synonymous mutation rate
along components of primate phylogeny, it was confirmed that the selection
pressure became more relaxed around that time. This confirmed that the V1R
receptor genes underwent relaxed pressure; therefore, the number of pseudogenes
increased showing the presence of four genes but the functionality of them has
not been determined. However, it has been determined that the four genes were
not conserved within the chimp species. In addition, most olfactory sensory
neurons present within an organism are bipolar cells. These neurons are
replaced about every 90 days and express a specific olfactory receptor. These receptors
allow the system to be specific for certain molecules but persistent for other
molecules. In mice, 16 olfactory receptor genes select for isovaleric acid, but
in humans, the same gene cluster was unable to be found. This piece of evidence
portrays that humans do not have the receptors specific for isovaleric acid. The
results from these series of tests show that the vomeronasal transduction
components became absent about 25 to 40 million years ago. However, the loss of
this transduction occurred in the same time frame that trichromacy appeared,
also known as color vision, portraying that perhaps pheromone signaling was
replaced with visual signaling.

After going over the structure of the assumed
pheromones and some of their analytical characteristics along with the
evolutionary adaptions the body has undergone throughout time, it is unlikely
that the human body actually possesses the ability to product pheromones or
even sense them. Although pheromones are steroids that are naturally made
within the human body’s glands, there is not enough concrete evidence on these
secretions to prove that they induce sexual drive. As science is always advancing
and changing, there is always the possibility that someone will prove this
theory wrong someday, but as of this point in time, your nose will not be able
to help you find your soulmate. 

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