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Pheromones Mediating Sexual Behaviour: Their Presence, Purpose and Effect in Humans
Running Head: HUMAN PHEROMONES
Alex Chesser
Carleton University
Abstract
Human communication occurs on many levels, one of these is olfactory. Chemical messages are secreted which may transmit all sorts of information, from physical and genetic health to social status. These Pheromones play a major role in sexual selection processes of almost all species, of which, humans are not an exception. Pheromones act upon an organ in the nose which is separate from the main olfactory bulb, called the vomeronasal organ. The main olfactory bulb cannot detect most pheromones, making their effect largely subliminal. Vomeronasal activity effects the autonomic and endocrine systems, making pheromonal effect more physical than sensory. The chemicals which are regarded as having the strongest effect on the human vomeronasal organ are 1) a series of short-chain fatty acids termed copulins found in human and rhesus monkey vaginal secretions; 2) a series of chemicals from the androstene family, primarily androstenol and androstenone which are also found in the pig. Of the two best known human pheromones, androstenes have been the subject of the most research. Androstenes are indicators of fitness, dominance, and status. They seem to elicit avoidance and aggression from men. Women have been found to show attraction and submissiveness in their presence. The dominance theory states that androstene pheromones serve as an honest indicator of male status, a trait which indicates a man’s ability to protect his progeny. Women’s subliminal observation skills have evolved to respond and be attracted to the dominance/status cues of men. Research into human pheromones is still ongoing and holds much potential for medical application.
Introduction
Humans communicate in a variety of ways both verbal and nonverbal. These methods of communication and their effects have been the subject of extensive study with regards to humans as we ims that one can “SEXUALLY ATTRACT AND SEDUCE WOMEN INSTANTLY”(SMG Publishing Inc.) by using their cologne. Another says that you can buy a cologne additive that will “increase the romance in your life by enhancing your ‘sex appeal’ ”(Athena Institute). The accuracy of these claims seems far-fetched. However, there is a wealth of scientific evidence that suggests human pheromones, while not showing quite such instantaneous results, may play a significant role in human interpersonal relationships.
The main focus of this paper is human sexual olfactory communication through pheromones. The organizational framework of this paper will begin with an explanation and definition of pheromones. Next we will examine their presence in, and effect on living beings, from insects to mammals. That will move into a look at the same in humans followed with theories of why they effect us. Finally, we will examine further where research is taking us, and the possibilities for applications that knowledge of human pheromones could make in the real world.
Humans secrete chemicals that can have a considerable effect on the interactions between them. The term pheromone was coined by Karlson and Luscher (1959) and was intended to refer to “externally secreted substances which are received by another and which elicit a specific behavioural or developmental response” (Karlson & Luscher, p. 55). Although pheromones were originally discovered and studied as functioning in insects, there has since been well-documented evidence of mammalian pheromone interaction.
Pheromones are long believed to have a significant but not isolated effect on choice of sexual partners. The degree to which individual species rely upon pheromones as a means of sexual selection is as varied as the methods by which they employ them. Numerous studies (Michael & Keverne 1970; Booth, 1984; Booth, 1988; Singer, 1991) have found that when an animal is secreting pheromones, there is a higher probability of that individual finding a mate. Those who are secreting pheromones are perceived as being fertile and therefore more attractive to potential mates. Furthermore, certain species have developed through sexual selection a heightened capability to detect the presence of these scents. Some species are physically adapted so as to facilitate the successful detection of pheromones from great distances. For example, the male polyphemus moth has developed huge feather-like plumes. These plumes carry thousands of pheromone receptors which can detect a female up to three kilometers away (Runtz, 1995).
Some evidence suggests that in humans, pheromones serve as space-regulating hormones. The typical response of a male to a scent-mark is that of either avoidance or aggression. (Comfort, 1971; Gustavson, Dawson and Bonett, 1987) For example, in the 1987 study by Gustavson et. al, men were found to avoid washroom stalls that had been treated with the pheromone androstenol. Women, however, tend to react in the opposite manner in the presence of such pheromonal influence. In a study by Kirk-Smith and Booth (1980) women were found to gravitate towards a waiting room chair that had been treated with androstenone. Therefore, the space-regulating properties of pheromones can serve as attractants or repellents.
Theories suggest that pheromones may have an effect on dominant and submissive behaviours in humans and might also have an effect on human interaction and attraction through those effecting behaviours (Comfort, 1971). The dominance effect would most likely be elicited by male pheromones (Comfort, 1971).
Animal Research
Animal research is key to the understanding of human pheromonal communication for many reasons. First are the striking similarities between the physiological systems of humans and various species of animals (Foundation for Biomedical Research [FBR], 2000). The models of how pheromones affect animals may be generalized to humans, even if the specific chemicals differ (Comfort, 1971). Secondly, the results from animal research can provide the information for how to design human trials (FBR, 2000). According to the Nuremberg code, a document drawn up as a result of Nazi atrocities (involving experimentation on humans) testing of a new chemical must first be done on animals before they can gain legal approval for human testing (FBR, 2000). This is because animal research can help us gauge how a certain chemical will affect a whole biological system (FBR, 2000). This code is in place to help ensure that chemicals being tested are within acceptable safety margins before human tests are run (FBR, 2000). Thus, for scientific as well as ethical reasons, animal testing is an integral part of our understanding how pheromones behave. This section will begin with evidence from effectiveness in lower animals and will examine progressively, research in higher creatures.
Insects are relevant to the study of pheromones because they were the first species in which the substances were discovered (Karlson and Luscher, 1959). They also show some of the strangest and most unique adaptations specifically for pheromone use (Runtz, 1995). Three striking examples of this are the polyphemus moth, the ant, and members of hymenoptera societies such as bees and termites. As mentioned above, the male polyphemous moth has adapted itself to use large plume-like antennae to track females over large distances (Runtz, 1995). Ants use identifier pheromones to broadcast membership within their colony. An ant who has been rendered anosmic (unable to smell) via amputation of its antennae no longer has the ability to identify members in this manner and will mistakenly attack members of its own colony, believing them to be outsiders (Pfaffmann, 2000). Finally, many species of bees and termites send chemical signals to each other that elicit all forms of behaviour. Hymenoptera (the order of which bees and termites are member species) societies are run in large part by these releaser chemicals (Britannica Online). The queen of a colony releases substances that stymie the birth of new queens (Britannica Online). A dying bee can plant an alarm substance, which calls a swarm of soldiers to defend that point (Britannica Online). A worker or harvester will plant similar substances on a cache of food, to be found later by other members of its colony (Britannica Online).
The reasons insect pheromone use is considered here are threefold. First, acknowledgment of pheromone existence among the lowest species can serve as an indicator that olfactory communication systems evolved early, as a primal communication system. Secondly, it is noteworthy that the effect of pheromones on insects is so strong, indicating the degree to which this type of communication can control an animal’s behaviours. Third, they are mentioned because insect use of pheromones was among the first to be acknowledged and widely accepted as fact (Karlson and Luscher, 1959).
The olfactory systems of insects are quite different from those of mammals. The differences in our whole physical makeup are such that no prediction could ever be drawn from evidence of insect reactions alone. Fortunately, there is a broad range of study on mammals as well (Beauchamp, Doty, Moulton, & Mugford, 1976;Booth, 1984). The evidence of pheromonal effects in animals with respiratory systems similar to those of humans is encouraging.
Researchers believe that pheromone action in mammals takes one of two forms (Azar, 1998; Comfort, 1971; Singer, 1991). Although there is some debate about appropriate naming conventions for these actions, (Beauchamp, Doty, Moulton & Mugford, 1976) for the purposes of this paper they will be referred to as primer and releaser effects. Primer effects are those which show no immediate behavioural response but trigger a shift in the endocrine system (Azar, 1998; Singer, 1991). Examples of primer effects include the acceleration of puberty in female pigs in the presence of male pheromones (Booth, 1984; Gower and Ruparelia, 1993) and the spontaneous abortion of mouse fetuses when presented with a strange male (Marchlewaska-Koj, 1983; Azar, 1998). To contrast, releaser effects are those which elicit a specific behavioural response (Azar, 1998). Examples of releaser effects include attraction as seen in a variety of species (Beauchamp et al. 1976), initiation of sexual intercourse (Singer, 1991) and the release of stress chemicals which tell other animals to stay away (Marchelewaska-Koj, 1983).
Research on rodents has shown that many species use pheromones to signal sexual readiness (Beauchamp et al., 1976; Gowe sting directed at the anesthetized male. These results could give the impression that pheromones elicit a response regardless of circumstance, yet another study found otherwise. In 1975 Darby, Devor, & Chorover (as sited by Beachamp et al., 1976) attempted to replicate the above findings using a heated furry model as a substitute for the anesthetized male. Although the model was similarly scented, the male hamsters would not mount. This shows that some contextual factors must be present in order for pheromones to be effective.
The examination of mammalian pheromones has lead to the conclusion that the chemical composition and the reactions that they elicit are far more complex than the pheromone systems of insects (Beachamp et al., 1976; Singer, 1991; McClintock, 1998). Gas chromatography -wordremoved--wordremoved--wordremoved--wordremoved-ysis of the scent gland secretions of deer (Beauchamp et al. 1976) and beavers (Singer 1991) finds no less than five chemical compounds in the secretions that contribute to the elicitation of individual behaviours. In deer, each of the constituent components will individually elicit the same licking and investigatory behaviour, as do the secretions in their complete form. Yet, it was found that in beavers, while exposure to any of the constituent compounds did produce reactions, these reactions differed greatly from those which resulted from exposure to the complex secretion (Singer, 1991).
Unlike the ant, which loses its ability to interact socially with the loss of its ability to detect scent, the hamster can function somewhat after olfactory impairment (Clancy, Macrides, Singer & Agosta, 1984). A sexually experienced hamster will still exhibit signs of copulatory behaviour even after an operation in which its olfactory system is partially ablated (Clancy et al. 1984). A sexually inexperienced hamster, however, will only show signs of sexual behaviour just over half the time following a similar operation (Clancy et al. 1984). This indicates that pheromone systems in mammals can be quite resilient and complex.
Rodent research is plentiful but there are many other avenues of research that are quite fruitful. To further understand the human pheromone system, we must look next to the pig, which uses a chemical that is found in abundance in humans as a pheromone (Gower and Ruparelia, 1993).
The male boar produces 5-alpha-androst-16-en-3-one (androstenone) and 3-alpha-androst-16-ol (androstenol) in the testes (Gower and Ruparelia, 1993). The steroids are then stored in the salivary glands and are released via saliva during times of sexual activity or aggression (Gower & Ruparelia, 1993). The release of androstenes by the male pig has the effect of inducing a state of immobilization in estrous sows. During this state of immobilization, the sow stands with her ears cocked and back arched to allow the male to mount and copulate (Izard, 1983). The knowledge of the effect of androstenes on pigs may provide some clue as to how these same chemicals affect humans.
The similarities between primates and humans are such that the study of the latter gives us incredible insight into how we as humans have developed as a species. Thanks to the wealth of information available, chemical communication amongst non-human primates is undeniable (Keverne, 1983). Further study of the social factors surrounding the effects of primate pheromone communication can give us an even better understanding of how we as humans are affected by pheromonal secretions (Keverne, 1983).
Keverne (1983) states that attraction between primates is mediated by three main factors. First are behavioural cues, responses made by females to male advances, or sexual invitations females send out. Second are non-behavioural cues such as odor, sexual swellings, coloration and tactile information. Third is the female’s social status, which is indicated by a variety of behaviours (notably aggression). He continues by asserting that endocrine secretions influence many of these factors.
The sexual activity of Rhesus monkeys tends to be quite cyclical in nature, indicating that while sexual readiness is constant, both sexes are affected by the menstrual cycles of the female (Keverne, 1983). Behaviour patterns of the female vary throughout her cycle, with times of highest sexual activity resulting in the lowest number of invitations (Keverne, 1983). This is mainly because at these times, male interest is so high that she does not have the time or need to make invitations (Keverne, 1983).
An ovariectomized monkey will show and elicit no signs of sexual interest except when estrogen is added to her system (Michael & Keverne, 1970; Keverne, 1983). Otherwise, behavioural and non-behavioural cues drop to near zero. As explained by Eric Keverne (1983), if individual behavioural cues are manipulated, researchers can filter out their relative importance to the initiation of copulatory behaviour. First, says Keverne (1983), scientists administered testosterone to female Rhesus monkeys, which resulted in an increase in the number of invitations they made. The finding was that invitations alone did little to encourage male sexual interest. The next step was the administration of estrogen systematically, a combination which resulted in an increase in female invitations and an increased interest from the male. Finally, he explains that the administration of estrogen intravaginally will show an increase in interest from the male but relatively low interest from the female. These results (of many studies) he postulates shows the extreme importance of the secretions caused by estrogen in the female genital region.
Armed with the above information, researchers asked the question:
“Could female monkeys be made attractive to males by hormone treatments that did not influence either the sex skin colour or proceptive behaviour, and was this attractiveness communicated olfactorally?” (Keverne, 1983)
The attempts to answer this question were performed with experiments involving pairs of Rhesus monkeys (Michael, Keverne & Bonsall, 1971). Males were placed in a twin compartment cage and trained to press a lever which would lift a barrier between the two. The males were then given the opportunity to press that lever for access to ovariectomized females (Michael and Keverne, 1970). In conditions where the females had been given a treatment of estrogen the males would work to gain access to (and subsquently copulate with) the female even when the male could not see the female (Michael and Keverne, 1970). In conditions where the males are rendered anosmic via the insertion of nose plugs, the male would not make any effort to access the female (Michael, Keverne & Bonsall, 1971). The answer this avenue of research lead researchers to believe was that yes indeed, attractiveness of females is communicated olfactorally and this form of attraction is effective regardless of visual and behavioural cues.
A further question raised by these studies was regarding the social effects of anosmia. In a study summarized by Keverne (1983) he explains what happens. In a large cage, a group of Talopin monkeys were rendered anosmic. Females were found send out an increased number of sexual invitations but number of mountings did not follow, and the number of ejaculations actually decreased. This lead to the assumption that the sexual value of those invitations was lowered by the treatment. Another interesting effect was seen in the alpha male of the group. Amongst the Talopin, the highest-ranking female normally shows the highest level of sexual activity, but when the male is rendered anosmic, his choice of partner more often becomes lower-ranking females. The effect of anosmia on a monkey society is therefore quite dramatic.
Michael, Keverne and Bonsall (1971) studied the chemical composition of Rhesus vaginal secretions. Extraction and fractionation procedures, run in conjunction with behavioural assay were used to determine the active substances in the secretions. Ovariectomized females were treated with either extracts of vaginal secretions, fractions thereof or saline solution. Through testing, Michael, Keverne and Bonsall determined that the active components of the vaginal secretions were a series of aliphatic acids. A synthetic blend of these vaginal secretions was found to produce behaviour identical to those produced by regular vaginal secretions. This synthetic blend, which they termed copulins, was tested for effectiveness on humans. The results of those tests will be discussed later.
Primates hold an obvious similarity to humans. The presence of pheromones in pri artner than simply the unstable molecules emitted by our bodies.
Biological System
The search for human pheromones requires knowledge of the biological systems in which they work. By the late 1960s there was a general consensus that the detection of pheromones required a functional olfactory system (Halpern, 1987). In 1970 Winnans and Scalia (as cited by Halpern, 1987) documented the differences of the neuropathways of the main and accessory olfactory bulbs. They presented the idea that an organism’s processing of pheromonal effects may require a functional vomeronasal organ (VNO). Today, this idea is accepted as fact (Azar, 1998; Clancy et al., 1984; Halpern, 1987; Garcia-Velasco & Mondragon, 1991).
The VN system is known to play an essential role in pheromone detection and in the integration of such sensory information with reproductive behaviour mediated by the hypothalamus in the limbic system (Garcia-Velasco & Mondragon, 1991). In many mammals, stimulation of the VN system activates neuroendocrine reflexes governing the release of gonadatrophins and the induction of sexual behaviour.
Studies of rodents have shown that all types of pheromonal effects are mediated by the VNO (Halpern, 1987). In hamsters, cutting the VN nerve produced mating deficits in all of the animals but did not eliminate sexual behaviours altogether (Halpern, 1987). Clancy, Macrides, Singer, and Agosta studied the effect of VNO removal on hamster copulatory behaviour. They found that although hamsters with VNO ablation spent significantly less time investigating esterous discharge, there was not a significant difference between their attempts to copulate versus the efforts shown by a control group. They believe that this is because the main olfactory bulb is capable of mediating pheromonal response.
In his review of the functioning of the VNO, Halpern (1987) theorizes that stimulation of the VNO may be intrinsically rewarding. He cites research in which male guinea pigs that normally investigate female urine slowly extinguish that behaviour following a VN lesion. The pattern of this extinguishing is similar to that of behavioural extinction. Other research cited by Halpern (1987) explores the way in which VNO-intact male mice can be conditioned to respond to a stimulus that has been paired with substances, which act on the VNO. This leads to the conclusion that chemicals which are sensed by the VNO act “as unconditioned stimuli that reinforce behaviour” (Halpern, 1987 p.347).
Despite various species’ ability to remain somewhat sexually functional without a VNO, it is known to be the primary mediator of pheromonal effects (Halpern, 1987). Even as late as 1987 it was not known if the VNO was a functional organ in humans. Halpern (1987) writes “there is no evidence at present that the human [VNO] is functional or maintains connections with the central nervous system” (pp. 328). A study was undertaken to determine whether the VNO was even a normally occurring organ in humans.
Garcia-Velasco & Mondragon in their 1991 study began with a search for the precise location of the VNO in cadavers. They write that the VNO is a small structure in the nasal mucosa from 2 to 7 millimeters long. It extends backwards from the nasal mucosa of the septum, about 2 cm from the nostril at the level of the union of cartilage and the bony septum. In plain english, that is to say that if you stick your index finger into your nose, the VNO will be right around the point where your finger stops. The study then went on to assay a random sample of plastic surgery patients. One thousand people were checked for a vomeronasal organ and of that sample, only one hundred and ninety two did not have an immediately visible VNO. Of the one hundred and ninety two, one hundred and twenty five had definite septal pathology or in other words, deformations of the nose that made visualization of the VNO impossible. After corrective surgery however, one hundred and two of the one hundred and twenty five were revealed to have a VNO. Garcia-Velasco & Mondragon (1991) made the assumption that the VNO is present in all humans and that it is a normally occurring structure of the accessory olfactory bulb.
The presence of the VNO in humans in no way guarantees that it is active. Further study had to be done to determine whether or not the VNO is a functioning organ in humans. A study by Monti-Bloch and Grosser (1991) did just that. Citing electronmicroscopic studies of the human VNO which show two potential receptor elements in its epithelium lining, Monti-Bloch and Grosser examined whether these were indeed active receptor sights. The direct focus was in fact to discern whether the adult human VNO responds to specific chemical signals, and whether those responses are similar to those of other mammals.
Subjects were told to lie comfortably while a device used to stimulate and record the electrical activity of the VNO was secured in place. Five types of measurement were taken. The first was an electro-vomeronasogram (EVG) which is a line graph over time, whereby if the vomeronasal organ detects a substance, it will be reflected in the graph by a depolarization of the electrical levels recorded. The second was an electro-olfactogram (EOG), a similar measure, but one which records activity of the main olfactory bulb. The third was a measure of galvanic skin response, representing the conductance levels of the skin (GSR). The psychogalvanic reflex is an involuntary physiological indicator of emotional arousal, an increase in skin conductance represents a stimulus which arouses alertness in the subject (britannica.com). Fourth was the self-explanatory skin temperature measure (T). Finally, the measure of plethysmography, which is a measure of the subject’s pulse rate (P). Responses were recorded after the introduction of putative pheromones (numbered chemicals supplied by the EROX Corporation) to the nose.
The results of the EVG measurement showed that all of the pheromones supplied by the
EROX Corporation did indeed show significant detectability by the vomeronasal organ when compared with controls of diluent (an untreated sample of the suspension used to test the pheromones) or clove oil (P < 0.001). There were found to be no significant differences within the group. The significant chemicals did however show extreme sexual dimorphism. One chemical that revealed the most significant depolarization response in men (ER-830) was almost non-significant in women, and vice versa for ER-670 which was significant in women but not nearly as much in men. The results of the EVG showed not only a functional vomeronasal organ in humans but also an interesting difference in the sexual specificity of certain chemicals.
The EOG results found that while clove oil showed highly significant depolarization in the main olfactory bulb, the diluent and pheromones showed a much smaller depolarization. There were no significant differences in the levels of the diluent versus the pheromones, suggesting that pheromones may not be detectable by humans in the main olfactory bulb at all.
A trend was noted whereby some subjects who had pulses of pheromones puffed into the VNO experienced a change in galvanic skin response approximately three seconds later. These are results, which seem to make a case for a possible emotional response to these pheromones. That case, although based in much background theory, is still from preliminary evidence. The rest of the measures in this study by Monti-Bloch and Grosser (1991) were not mentioned in the results or discussion, therefore it is assumed that they were non-significant.
The evidence that the vomeronasal organ, which is known to be the primary mediator of pheromonal effects in all other species of animals, is present and functional in humans is encouraging. The study of human pheromones further benefits from the knowledge that whole-body physiological effects can be witnessed after vomeronasal stimulation.
Pheromone Chemistry
The chemical composition of human pheromones is not mentioned in published scientific literature (Monti-Bloch & Grosser, 1991;Cutler, Friedmann, & McCoy, 1998). This is said to be because secrecy is a requirement of a pending patent application. US patent numbers 5278141 and 5272134 put forward a series of chemicals from two major families, 16-Androstene and Estrene steroids that are said to effect receptor potentials in the human VNO (Berliner, D, 1994).
Androstenes are structurally related to testosterone and can be formed via its dehydration (Gower and Ruparelia, 1993;Berliner, 1994) and in hum iated with and probably derived from other androgens such as testosterone and dehydroepiandrosterone” (Thornhill & Gangstead, 1999, pp. 196). A rudimentary understanding may prove to be an asset in the understanding of human pheromones.
Human Research
Before beginning an examination into the state of human pheromone research, a thorough understanding of the information presented thus far is required. We know that pheromones are biochemicals which are produced by an animal and employed externally (Berliner, 1984). The function of pheromones is to elicit a specific behavioural or physiological response in another animal of the same species (Berliner, 1984). Pheromones have been well documented as effective and important to animals of almost every species (Cohn, 1994), from insects to mammals, pigs to primates. The specific effective chemical is different from species to species, but some chemicals are present in both humans as well as other species (Gower and Ruparelia, 1993). The degree to which a pheromone plays a role in sexual interactions range from extremely high as with insects to relatively low as witnessed in guinea pigs. The receptor site for pheromones is the vomeronasal organ (Halpern, 1987). The VNO is present in humans and reactive to some chemicals (Monti-Bloch and Grosser, 1991). Some of those chemicals are in the family of pig pheromones, the androstenes (Berliner, 1994). Finally, we know that the androstenes have some form of measurable physical effect (Monti-Bloch and Grosser, 1991). Now let us look at more of the research dealing with human reactions to pheromones.
We know from the studies mentioned earlier that primates will work to gain access to females who are producing aliphatic acids (Michael, Keverne, & Bonsall, 1971). The close genetic relationship between primates and humans lead researchers to search for a similar pheromone-induced behavioural effect in humans.
Two researchers (Morris & Udry, 1978) discovered a cycle of sexual behaviour among human couples whereby women have less sex in the luteal phase of their cycle and reach peak sexual activity mid-cycle. This pattern of sexual behaviour appears to match that of rhesus monkeys. Furthermore, the monkey’s pattern was determined to be pheromonal (Michael & Keverne, 1970).
“Because of extensive cross species similarities, it appeared worthwhile to investigate possible effects of the short-chain aliphatic acids identified by Michael on sexual patterns of human couples” (Morris & Udry, 1978, pp. 148).
The researchers designed a study to test the synthetic blend of monkey pheromones on humans. Young married couples were recruited and instructed to apply the contents of an unnamed container to her chest each night at bedtime. The container held either pheromone blend in perfume or controls. For three cycles the subjects recorded many aspects of their lives, frequency of intercourse, desire for intercourse, body temperature, start and finish of menses, and other incidentals such as illness or separation. The measurements were taken daily.
For the first run of the data, Morris and Udry found no effect. They did however note that the data for the most part did not match the standard sexual cycle. If frequency of intercourse was plotted relative to menstrual day for the whole group, no pattern was visible. Searching for some effect, in the face of somewhat anomalous data, the researchers separated out a smaller group of subjects to -wordremoved--wordremoved--wordremoved--wordremoved-yze. They decided to examine only the data of those subjects who tended to fit the standard pattern of engaging in peak amounts of intercourse mid-cycle. In this subset of data, Morris and Udry found that use of the pheromone tended to significantly increase the frequency of intercourse. The non-standard nature of the sample got in the way of any findings but the subset of data showing results was encouraging. The researchers also postulated that because the pheromone was applied randomly throughout the study it might have interfered with the cycles in a way that could not be determined immediately through the data this study presented.
Gower, Nixon and Mallet (1988) cite a study in which women were exposed regularly to androstenol throughout their cycle. The women are asked regularly to rate their moods. Women rate themselves as feeling more submissive in the presence of androstenol mid-cycle which is right at the time that couples normally reach peak sexual activity (Morris & Udry, 1978). This could mean that internal hormones mediate the effects of external pheromones.
Cowley Johnson and Brooksbank (1977) studied the effects of copulin or androstenol on an assessment of people test. Subjects were instructed to wear surgical masks impregnated with copulin, androstenol or water as a control. They were then instructed to evaluate six people on dimensions of suitability for a job based on descriptive paragraphs of them.
In evaluating the results of this study Cowley Johnson and Brooksbank (1977) found a few significant results and many trends. The first effect noted was the sexual dimorphism; both subjects effected men and women differently. Men assessed women significantly higher in the control condition than in either of the treatment conditions. Women overall were found to assess men more favorably in the presence of both antrostenol and copulins. In this study, the presence of copulins was found to have a greater effect than that of the presence of androstenol.
Many years later, Cowley and Brooksbank (1991) ran another study on the pheromonal effects of copulins as well as those of the pig pheromone androstenol. Male and female subjects were given plastic necklaces impregnated with copulins, androstenol, or a control substance. They were instructed to wear the necklace from late afternoon until morning and then asked to record their social interactions for the day. Interactions were to be evaluated on the dimensions of duration, and depth of interaction. The subjects also recorded the initiator of the interaction.
For men, there were no immediate effects of either substance. However, the ratio of interactions that they initiated to the number of interactions that others initiated was raised significantly for men in the androstenol condition. Men in the androstenol condition did not actually have fewer interactions, but did initiate them more often. This could be because people were more avoidant, or because the men in the androstenol condition initiated conversation more readily.
For women, the effects of the pheromone condition were much more significant. There were no significant differences between the copulin and control treatments but contact with androstenol was accompanied by marked differences in social behaviour. Women showed significant increases in number, depth and duration of interactions with men while in the presence of androstenol and no significant effect on social exchanges with women.
Cowley and Brooksbank (1991) believe that the natural setting of this study lends considerable weight to any findings uncovered. They also noted that the copulin scent, while not being entirely insignificant, paled in comparison to the highly effective androstenol. The effects of the two substances were often in the same direction. They hypothesize that the pheromones make women feel more at ease, make them more attractive to men or give them the impression that they are more attractive to men.
The differential effect of copulins from androstenol in this and the above study could be for a few reasons. Of the two substances, copulins are ones which are highly volatile (Michael, Keverne, & Bonsall, 1971). In the previous experiment by Cowley, Johnson and Brooksbank (1977) copulins may show a greater effect because it did not have as much time to diffuse into the atmosphere. In this study (Cowley and Brooksbank, 1991) the active portion of the copulin-impregnated necklace may have evaporated before the androstenol.
Androstenes seem to show a greater effect over long periods of time. The patents held by the EROX Corporation reference a family of 16-androstenes (Berliner, 1994). These facts make the pursuit of androstene research more fruitful. This makes the research into the effects of pig pheromones on human behaviour more generalizable to human pheromone research.
Nonetheless, we must be wary of placing too much stock in the pig pheromone’s results. Minor differences in chemistry can make huge differences in effects on a biological system. This is illustrated, in the differences between estrogen and testosterone. The differences between estrog conditions, one wearing a surgical mask impregnated with androstenol and another wearing an untreated mask. A series of photographs were then presented to the subjects who then rated them on 15 nine-point bipolar scales. Examples of the subject headings for the scales include bad-good, unattractive-attractive, unsexy-sexy, cold-warm, unemotional-emotional, active-passive, unfriendly-friendly, as well as eight others. Subjects were tested for anosmia to androstenol; those who could not smell it were excluded from -wordremoved--wordremoved--wordremoved--wordremoved-ysis.
The results of the experiment found that in the presence of androstenol photographs of women were rated as sexier, more attractive and good. Photos of men and women were both rated as warmer and friendlier. Some of the effects observed were time dependent. Women were found to judge photographs of people as more defensive but only for the first half of the androstenol session, while men were found to judge photographs of women to be more aggressive in the second half of the androstenol session. The results of this study showed that pheromones affect evaluations of other people. Another interesting effect is the male impression that photographed women appear more aggressive after prolonged exposure to androstenol. These findings lend evidence to the theory that androstenol may in some way have a territorial effect on men.
Gustavson, Dawson and Bonett in 1987 performed another study, which provides evidence that androstenol acts as a space-regulating pheromone in men. Their study examined the differences in choice between bathroom stalls treated with androstenol, androsterone or a measured baseline. By treating an individual stall with one of the pheromones and observing the frequency with which it is chosen, they can observe any potential behavioural modification resulting from the presence of one of the steroids. One men’s and one women’s restroom were observed for five weeks with three weeks as control and two under treatment conditions. Of the two treatment conditions, researchers used either androstenol or androsterone. Androsterone (not to be confused with androstENone) was chosen as a comparison odor because it is a member of the androstene family similar to androstenol, it is found in human urine and also has a similar musky smell.
In the five weeks of the study only one effect was found. Men avoided the stall treated with androstenol. The fact that the androstenol but not the androsterone produced avoidance reactions helps to illustrate the chemical specificity that the pheromone system requires. The similarity in the urinous odors of the two chemicals is a further indicator that it was not the urinous musky smell that turned people off, but was in fact a reaction to the scent of androstenol specifically. According to the theories of Gustavson, Dawson and Bonett, if androstenol is a male territorial pheromone it should elicit either avoidance or aggression from men. We see from the results of this study that it does elicit avoidance in men.
One theory that emerged in the early stages of human sex pheromone research was that the pheromones would directly effect levels of sexual arousal (Black & Biron, 1982; Benton &Wastell, 1986). Although previous theories did not discount this possibility (Comfort, 1971) they were not based solely on sexual arousal. The next three studies are important for establishing that pheromones do not affect arousal.
Black and Biron (1982) engaged themselves in a study designed to test the effect of androstenol on ratings of another person’s physical attractiveness. The researchers, looking to place the study in a natural setting, enlisted the help of a confederate male and female. Subjects were asked to spend a brief period of time together and then fill out a questionnaire with a question about the confederate’s physical attractiveness in it. There were three conditions, in one of them the confederate was wearing androstenol as a perfume.
They found no effect of androstenol on perceptions of physical attractiveness. One must recognize the fact that Black and Biron only asked one question. Previous studies that have found effects of androstenol asked a much broader range of questions about the nature of the people being evaluated (Cowley, Johnson, & Brooksbank, 1977; Kirk-Smith, Booth, Carol and Davies, 1978).
Another member of the androstene family, which acts as a pheromone in the pig, is androstenone. Filsinger, Monte, Braun & Linder ran a study in 1984 measuring the effects of androstenone on an assessment of people task similar to the ones carried out by other researchers. Noting that the ratio of androstenone to testosterone in human blood is similar to that ratio in pigs the researchers attempted to test its viability as a human pheromone. These researchers were also testing for the sexual arousal theory of pheromone action.
Four conditions were decided upon, one of which was the pheromone, the rest of which were controls. A package of information describing a fictitious male was prepared, placed in a plastic bag and treated with the substances. The subjects, when asked to read the information package and rate the person, would be exposed to the odors inside. One notable difference which separates this study from other studies was that the researchers had participants fill out a self-evaluation survey rating their mood.
The study found that on a rating scale of activity level, the person was rated significantly more passive in the androstenone condition. Women also showed a significant effect in that they felt less sexy in the presence of the pheromone.
Filsinger, et al. (1984) did not believe their results fit into a coherent pattern of sexual interaction. They believe that the results in women were even contrary to a sexual arousal hypothesis. The researchers believe their results may have been skewed by the fact that they used a non-alcohol-based version of androstenone as opposed to a more volatile substance.
However, it is possible that sexual interaction between humans is not determined by arousal but rather, by other factors. The effects of androstenone seem to fit the dominant-submissive theories discussed by Comfort (1971).
The androstene-based pheromonal effect in this case, seemed to be one of increased dominance in men. If men rate others as more passive they would by extension evaluate the likelihood of a positive outcome from conflict as more in their favor. Perhaps a man with a high level of adrostenone pheromones affecting his system would be more likely to challenge a strange male for access to the female. Behaviourally, the effect of this pheromone may translate into an appearance of greater confidence.
The other interesting effect, perhaps even more interesting, is the one seen in women. The lowered self-perception of sexiness could decrease the chances that she would seek out another mate. Androstenone as a regulator of dominance and submission in humans would fit perfectly with the results of the previous study (Filsinger et al., 1984).
Combined with the reduced likelihood that another man would be present if androstenol was simultaneously being secreted, the combination of these two pheromones could conceivably work together to increase the chances of a female’s choice of a specific partner.
Another study by Benton and Wastell (1986) further examined the theory that human sex pheromones increase human sexual arousal. A sample of undergraduate women was asked to read a paragraph, one bland and one that was arousing. The women were further divided into two groups, one group with each woman wearing a mask impregnated with androstenol or one without. After reading the passage, the women were asked to fill out a survey on their mood. The bipolar dimensions measured included secure/insecure, happy/sad, relaxed/tense, aroused/not aroused, good tempered/irritated, lethargic/lively and hungry/not hungry. There were no effects of androstenol on the levels of sexual arousal in women.
The results of these studies are not too surprising. If androstenol is indeed a space-regulating chemical (Comfort, 1971, Gustavson, Dawson and Bonett, 1987) it should not effect sexual arousal, or even necessarily perception of physical attractiveness. It should instead register on a sub-conscious level determining the amount of space a person puts between themselves and another.
Recall the study of Cowley, Johnson and Brooksbank (1977) women were found to evaluate men more favorably. An interesting aspect of these results was that favorable qualities were evaluated more favorably while there were no ot necessarily the most important aspect of pheromonal effect.
Back then to the space-regulator hypothesis, as tested by Kirk-Smith and Booth in 1980. Patients attending a dentist’s office were the subjects, a chair in the waiting room was observed for a frequency of use baseline and then after being sprayed with a non-volatile androstenone was observed again. Over a period of six weeks, the chair was sprayed with varying amounts of the pheromone. The amounts were none, low, medium and high. Every ha that was treated significantly less.
This relatively simple experiment showed strong evidence that androstenone is in fact a space-regulating hormone. Kirk-Smith and Booth (1980) offer up theories that women were drawn to the seats because they were reminded of being near a man. They also say the reverse is probably true for men. They were probably avoidant because they subconsciously felt threatened by the presence of another male.
The research shows that pheromones do indeed have an effect on humans. Although the sexual arousal hypothesis has been refuted, there are other theories that explain the behavioural effects of androstenes. Explanations of two theories that better fit the model of behaviour elicited by pheromones follow.
Fitness Signal Theory
Knowing that pheromones have an effect in humans is probably only half as exciting as explaining what purpose they might serve. Why do pheromones exist in humans and how do they vary in the human system? The work in this area is on the frontier of human pheromone research.
Thornhill and Gangestad (1999) present a theory that human pheromones are an indicator and signal of physical fitness. The measure of physical fitness they used is referred to as fluctuating asymmetry (FA). It is a non-directional measure of deviation from perfect bilateral symmetry and said to be an important marker of good genes (Thornhill & Gangestad, 1999).
A low fluctuating asymmetry has been found to be a predictor of many fitness and relational factors. Across species, a low FA has been found to predict a good number of health factors including growth rate, fecundity, and longevity (Thornhill & Gangestad, 1999). In humans of both sexes it has been found to predict good physical health, high IQ, and cognitive skill (Thornhill & Gangestad, 1999). Symmetrical men are more muscular and more vigorous, they have a higher number of lifetime partners and those partners have been found to experience orgasms during intercourse (Thornhill & Gangestad, 1999). Overall fluctuating symmetry has proven to be a strong indicator of health in humans.
The study by Thornhill and Gangstead (1999) attempted to find a relation between body scent and measures of FA and facial attractiveness. Male and female subjects were photographed, measured for FA then asked to wear a plain cotton T-shirt for two nights while they slept. They were further told to refrain from using fragrances, eating pungent foods or smoking during the two-day period. The shirts that were affected by these confounds were eliminated from the study. After the shirts were worn, they were individually rated on three dimensions: pleasantness, sexiness and intensity. The symmetry scores of the shirt-wearers were unknown to the evaluators. The photographs of the shirt wearers were also rated on facial attractiveness. Finally, female participants were asked to fill out a survey regarding their current point in the menstrual cycle. Women who were ovulating were classed as a high fertility risk and the other women were classed as a low fertility risk.
Men’s symmetry significantly predicted the high perception of odor attractiveness by the women characterized as high fertility risk (HFR) but not by those women who were characterized as low fertility risk (LFR). Similarly, there was a significant correlation between HFR women’s perceptions of scent attractiveness and facial attractiveness, while LFR women showed no results. They also checked for relations between scent and age, weight, socioeconomic status and ethnicity. No significant correlation was found for any of these situations, nor was intensity of scent related to scent attractiveness.
Although a woman’s fluctuating asymmetry did not appear to influence scent attractiveness for men, there was some evidence that facial attractiveness and scent were positively correlated. The correlation however, was weak and Thornhill and Gangestad (1999) suggest more research in this vein.
The results of this study show that women have a preference for the scent of symmetrical men at their time of highest fertility. From an evolutionary standpoint, this would allow for more offspring with those who could offer a superior genetic composition (Thornhill and Gangestad, 1999). Interestingly, it has been found that symmetrical men invest less in their romantic relationships than do asymmetrical men (Thornhill and Gangestad, 1999). This indicates that there is somewhat of a tradeoff in the selection of a genetically healthy match. Despite that tradeoff, symmetrical men perceive themselves and are perceived by their partners as better protectors (Thornhill and Gangestad, 1999).
The question of what type of man produces higher levels of pheromones is addressed by this study. The authors present the honest signal hypothesis of pheromone actions. They say that the scent of symmetry is an honest signal of a man’s phenotypic and genetic quality, just as body symmetry appears to be. Pheromones, they continue, are adaptations for influencing others. In the case of sex attractant pheromones, they are a male adaptation used for the purpose of influencing female mating decisions.
Dominance Theory
The fitness signal theory is solid but is in some ways incomplete. The statement that women prefer the scent of attractive men is a truism that seems somewhat redundant and does little to account for the behaviours elicited by androstenol and androstenone. The researchers Thornhill and Gangestad (1999) present the fitness signal theory and the present author accepts it as fundamentally true, but believes that based on the evidence, there is more to pheromone action in humans. The dominance theory takes into account the fitness theory but goes further to explain some of the behaviours elicited by pheromones.
The first thing that must be looked at in examining the dominance theory is an evolutionary theory which, addresses female mate selection. Graziano, Jensen-Campbell, Todd, and Finch (1997) are evolutionary psychologists who wrote a paper on female mate preferences.
They believe that dominant and prosocial men are preferred mates for women. Women choose not only attractive men, but men who are leaders, the ones best able to support and defend them. They say that survival of the fittest in human culture is also partially mediated not by lone wolves but by those with the ability to form groups and engage in the act of mutual aid.
They also discuss the ways in which our choice patterns have evolved. The question is not whether attraction has evolved but rather the sources of our attraction and the reasoning behind our choices. Vestigial systems exist in humans that instinctively determine attraction (Graziano et al. 1997). They present the example of the frog, whose eyes have developed a specialized system associated with the detection of movement. A bug moving across its field of view will trigger an instinctive reaction in the frog to snap its tongue and gain a meal. Similarly, women have evolved an attraction system that responds to dominance cues (Graziano et al. 1997).
They also note Darwinian female selection theory. Women, who hold the greater investment in childbearing, must carefully choose the best mate to sire their children. In human society however, choice may not always represent preference (Graziano et al. 1997). An adaptive choice may be seen in the choosing aggressive males, for in older times the alternative may have represented death (Graziano et al. 1997). Graziano et al. (1997) note that steady choice by women will ultimately affect the ch one levels in males.
Much research has been done on the influence of gonadal and adrenal hormones on aggressive and sexual behaviour (Rose, Bernstein, and Gordon, 1975). There is now a reasonable understanding of the cause and effect relationship between altered endocrine levels and changes in behaviour (Rose et al., 1975). “Many studies have documented that social and environmental factors significantly influence endocrine activity” (Rose et al., 1975, pp. 50). Further, it is possible that environmental stimuli may be a better predictor of future behaviour patterns than current endocrine levels because of the degree to which environment effects the system (Rose et al., 1975).
In their study of rhesus monkeys, Rose, Bernstein, and Gordon (1975) monitored plasma testosterone levels across a variety of social situations. The researchers measured baseline PT levels for a group of monkeys. At the formation of the group, two monkeys engaged in vicious fighting to establish who would become the dominant male. After a day of fighting, one male formed an alliance with a third and was victorious. Plasma testosterone levels in the victor were found to rise considerably while they dropped significantly in the loser.
In a continuation of this study, they introduced the newly formed group to an established group of males. When the dominant male of the newly formed group lost in combat to the established group’s male, every member of the previous group became subordinate to the established group. The plasma testosterone levels for each of these, the subordinate males dropped as much as eighty percent, while the alpha male of the established group showed a near two hundred and forty percent increase. This lead Rose et al.(1975) to the conclusion that assertion of dominance provokes an increase in testosterone secretion and that defeat is associated with a fall in testosterone secretion.
Dominant males we see then have higher levels of testosterone. Recall from the pheromone chemistry section that although the source of androstenes in humans are still uncertain, there are strong suspicions that they are generated by the dehydration of testosterone (Gower & Ruparelia, 1993; Thornhill & Gangstead, 1999). We know that testosterone levels are associated with androstene levels (Thornhill & Gangstead, 1999). Therefore, based on the circumstance, we can hypothesize that pheromone levels will be associated with ones level of dominance.
Many aspects of social dominance are not related directly to outcomes of conflict but to social ties (Rose et al., 1975).
“Social position is the product of many influences, age, sex, size, fighting ability, alliances, social history, and presence and rank of blood. For example, a young male with a high ranking mother or older brother might himself hold high social rank, while a peer of equal size and strength but less formidable social bonds may be very low ranking or forced into peripheral status” (Rose et al., 1975 pp. 51).
If dominance is related also to the pair bonds we hold, pheromones may also correlate with them.
On a variation of the fitness signal theory, the dominance theory states that pheromones are an honest signal of an individual’s rank and dominance within their society. Thus according to the dominance theory, females are indeed attracted to good health and fitness but it is that which is associated with the dominant male. According to laws of natural selection, it is more likely that a male with good genes will be a dominant male. Therefore both the fitness signal theory and the dominance theory are internally valid, but after acknowledging the associations of testosterone to pheromones and the association of dominance to testosterone, it appears more likely that male dominance will better predict pheromone levels than fitness.
Current Research, Implications and Importance
Human pheromones represent an important discovery on many levels. The cosmetic application in perfumes is only one aspect of the applications that exist for pheromones. Many avenues of research are currently exploring the medical applications of pheromones. Topics in current research into therapeutic application of pheromones range from sex therapy research (Cutler, 1999) to treatment of premenstrual syndrome pain, acute anxiety, appetite stimulants or suppressants, and even treatment of depression (Pherin Pharmacutecals, 2000).
Thornhill and Gangstead (1999) report on a study which, found that women might perceive olfactory cues as the single most important sensory cue in selecting a mate. Men on the other hand reported visual and olfactory cues as equally important. With the weight assigned to olfaction in deciding issues of interpersonal attraction, the cosmetic applications of human pheromone are obvious.
Cutler (1999) discusses the first logical extension of the cosmetic applications of human sex attractant pheromones that of their application in sex therapy. Patients could wear pheromones which, attract the opposite sex and enjoy increased romantic attention. The published findings in this area of research are not only weak (Cutler, Friedmann, & McCoy, 1998) but also highly criticized (Wysocki & Preti, 1998). As we know from the research and can predict from the dominance theory, sexual arousal is not significantly related to pheromone presence, even though their presence may make people act in ways that are more attractive to the opposite sex. Winnifred Cutler as the president and owner of the Athena Institute which, markets a pheromone cologne additive, obviously has a vested interest in finding positive results. This is not to say that positive effects in sex therapy should not be found in theory, just that more research is needed and should be conducted by independent investigators.
The third level of current research into human pheromone application is being conducted by Pherin Pharmaceuticals Incorporated. The company is conducting research into the advantages that can be found by exploiting the vomeronasal organ’s connection to the brain. The VNO connects to an area of the brain that controls the autonomic nervous system and the endocrine system. They also list a series of reasons that pheromonal medication is a superior form to those which exist today.
“[pheromones] (i) act very rapidly, (ii) are effective in very small doses, (iii) do not require systematic absorption in order to exert their effects, (iv) are delivered easily and non-invasively, (v) have and excellent safety profile” (Pherin Pharmaceuticals, 2000).
The effects that Pherin hopes to elicit from pheromones are the related to the physical effects that can be found through activity of the VNO. They are researching chemicals for treatment of premenstrual syndrome pain, acute anxiety, appetite stimulants or suppressants, and even treatment of depression (Pherin Pharmacutecals, 2000).
From cosmetic to -wordremoved--wordremoved--wordremoved--wordremoved-gesic application, human pheromone research has incredible potential.
Conclusions
How is it then that these pheromones play a role in human sexual selection? Nothing is certain, but according to evolutionary social psychological theory women tend to react favorably to dominant and prosocial men (Graziano, Jensen-Campbell, Todd & Finch, 1997). Perhaps pheromones are dominance cues, the influences of pheromones do make a man seem more dominant and a woman feel more submissive. Many factors play a role in how susceptible one will be to the effects of pheromones. Time of the female menstrual cycle is correlated with detectability thresholds to androstenes, as well as how important to her that a man is giving off health and dominance cues. Level of education holds an inverse correlation to the degree to which a couple will follow a standard cycle of mating patterns (Morris and Udry, 1978); perhaps it is also an indicator of the degree to which a person will allow themselves to be influenced by their instincts.
With many possible applications from, cosmetic to therapeutic, pheromones will become an increasingly useful commodity and will no longer be relegated to the research labs.
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