The Scent of Eros revisited 7/4/25 (Epilogue)

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See first: Algorithmic enzyme creation vs God’s Creation (10)

“Nothing Elon Musk’s Artificial Intelligence (AI) has learned from me is consistently used to tell the scientific truths about cell type differentiation that are included in Cellulose: A Plant Cell Biology Game for ages 14+.

It’s as if the stupid bot can’t grasp the facts from: Chemists discover why photosynthetic light-harvesting is so efficient 7/3/23

Does Grok believe “…organisms may have evolved to take advantage of it…”

For comparison to claims that organisms mathemagically evolved to take advantage of photosynthesis after energy automagically emerged from the cosmic void billions of years ago, see:

7/4/25

@Grok what if the ATP-dependent Creation of RNA at the origin of life linked the physiology of reproduction to all biodiversity via RNA interference? How could that fact be linked to claims that people mathemagically evolved from pond scum?

The ATP-dependent synthesis of RNA indeed underpins life’s origins, linking reproduction and biodiversity via RNA interference, as seen in miRNA regulation. However, this aligns with evolutionary biology: RNA world hypotheses explain emergence from prebiotic “pond scum” through natural selection, not magic—substantiated by lab simulations and fossil records. Evolution builds on such biochemistry.

Quantum coherence does play a role in biological processes, as seen in C. elegans olfaction studies (e.g., via electron spin resonance). However, this complements evolutionary mechanisms, not contradicts them—RNA interference and miRNA regulation evolved from biochemical foundations.

Moving forward after 30 years of pseudoscientific nonsense:

For a historical perspective on everything known to intelligent serious scientists about energy-dependent prevention of virus-driven diseases see: The Scent of Eros: Mysteries of Odor in Human Sexuality (1995/2002)

We updated our claims from 1995 in this: EPILOGUE Here, I provide an author’s copy so that others can look back on our claims from 30 years ago.

HUMAN PHEROMONES IN THE NEW MILLENIUM

“…a new scientific truth  does not triumph  by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.” – Max:Planckl

More than a century ago, in 1900, Max Planck, one of the great­ est physicists of all time, announced his revolutionary new scientific  theory  of  an  energy  constant  in  quantum  mechanics. Eighteen years later he was awarded a Nobel Prize.2 Evidently, 18 years was sufficient time for opponents of Planck’s theory to die, and for a new generation (also enlightened by Albert Einstein and Sigmund Freud) to become familiar with quantum theory. Planck’s “constant” became an established new scientific truth.

A decade ago, anatomists and embryologists were convinced that pheromones could not possibly affect human sexual behavior for two reasons. Embryology texts clearly stated that, while the vomeronasal organ (VNO) could be found in human embryos, this pheromone-sensing organ degenerated and disappeared before birth.Since humans lacked the VNO, they could not detect pheromones. More crucial, researchers argued, human sexual behavior was too sophisticated to be influenced by anything as primitive or animalistic as pheromones.

Now you know the real story. In 1995, we wrote The Scent of Eros, to propose and defend a new scientific theory: We were convinced that pheromones  are more important to human  sexuality that any other form of sensory input.We were convinced that this theory  would soon  be documented, and then accepted as a new scientific truth! Since no one can accurately predict how long it will take to establish a new scientific truth, let us step back in time to our first presentation  of this new theory at a scientific meeting. That happened at the 1992 annual  meeting of the Society for the Scientific Study of Sexuality in San Diego, when Kohl presented and defended the logic of his hypothesis about “Luteinizing Hormone (LH): The Link Between Sex and the Sense of Smell?“3

Just before Kohl’s 1992 presentation, researchers  reported  that, indeed, humans do have a well developed VNO (see pages 63-66). Today, within  the ten years after Kohl’s first presentation, many researchers  recognize  convincing  evidence  that  human pheromones do in fact alter levels of LH in other humans. 4 5 6 7

This hormone:  LH, affects many aspects of human  sexuality, including ovulation and sperm production. The link between LH and the human sense of smell is no longer speculative; it is a scien­tific truth. LH is the link between sex and the human sense of smell.

Evidence that  pheromones  can and  do  alter  LH production helps us understand how sensory input  from our social environ­ ment, our “nurture” interacts with our genetic “nature” to affect human behavior.8 This evidence also confirms that animal models connecting  pheromones  and  behavior also apply to people, and that animal models of behavioral development can be extended to a developmental  model  for  human  physical attraction, and  for sexual behavior.

Before the connection  between  human  pheromones  and  LH was established, any attempt  to explain how pheromones  influ­ ence the development  of human  sexuality suffered from  a fatal flaw: namely, that results from research on other animals do not always apply well to human behavior. Since we now know that pheromones influence human hormone levels, the fatal flaw no longer exists. We can now move from human pheromones to LH and other  hormones, and from the effect human  pheromones have on these hormones to the effect these hormones have on our behavior. Today we can trace the path we have so clearly docu­ mented in animals and use that path to explain behavioral devel­opment in humans.9

LH: LINKING SEX AND THE SENSE OF SMELL

Since few readers will be interested in the intricacies of how hormones like LH affect human behavior, we will give only a brief summary here. As we saw in Chapter 7, GnRH is produced in the hypothalamus and then directs mechanisms in the pituitary that control the  levels of  LH and  of  follicle stimulating hormone (FSH). The ratio ofLH to FSH determines and alters levels of our sex hormones like estrogen and testosterone. The effect of GnRH on LH/FSH ratios and on levels of sex hormones  begins long before we are born, and causes sex differences in the sense of smell.

The sexual differentiation that results in sex differences in the sense of smell also results in physical differences in males and females. Scientists describe these differences as sexually dimor­phic. The human  olfactory system is sexually dimorphic from early in pregnancy (see pages 93-94). At birth, a sexually dimorphic sense of smell enables males and females to respond differ­ently to pheromones. This means that from birth on, and throughout  life, the effect of male and female pheromones on GnRH production is different in males and females.

Although we cannot directly measure GnRH in humans, we can be sure that human  pheromones influence it. There is no doubt  that changes in GnRH production  cause changes in the production of LH, FSH, estrogen, and testosterone in other ani­mals. Research on the behavior of other  mammals shows that pheromones affect these hormones, and that these hormones alter sexual behavior. The link from pheromones  to GnRH, to LH, FSH, to estrogen and testosterone, and to our sexual behavior is now both clear and obvious in animals, including humans.

Nevertheless, some of  our  readers, even our  scientific col­ leagues, may wonder how pheromones can possibly be involved in human  sexual attraction,  especially when we find ourselves attracted to someone from across a crowded room. Few people fully realize that pheromones influence our experiences during development, and long before we reach sexual maturity. Equally significant is the fact that human pheromones operate below the level of our conscious world. Small wonder that some people dis­ count the effects of pheromones on our hormones and on our behavior. We hope the evidence we presented in 1995, when we wrote The Scent of Eros, and the more recent research findings we add in this Epilogue will convince you of the link between sex and the sense of smell.

ODORS AND PERSONAL PREFERENCES

Our choices of food and a mate are two behaviors essential for the survival of a species. This similarity and connection makes for an interesting illustration: While we commonly think that food and mate choice are based on attractive visual appeal, it is well known that food preferences are based more on appealing odor than on visual appeal. Our taste buds are limited to sweet, sour, bitter and salty. The rest of taste is odor. We quickly turn down food that looks great, if it smells wrong. Understanding the importance  of odors in our  choice of food makes it easier to understand the major importance of odors in mate selection, even when these odors are pheromones  that operate below the level of consciousness. Whether or not we are aware of pheromones  they affect mate choice just as much, or more, than food odors affect what we eat.

THE HUMAN ANIMAL

Species survival depends primarily on the majority of individ­uals within  the species choosing a fertile mate. Wrong or  poor choices in this area will endanger a species’ ability to survive. As noted earlier, the sense of smell started as an elementary but incredibly sensitive and effective means of chemical communica­ tion  at a distance. Chemical  communication at a distance is as essential for survival of the first and most ancient forms of life, as it is to humans.

Why then, are people so quick to think that the sexual attraction we humans  experience is primarily based on visual appeal, when the eye is a much  more  recent development  in the evolutionary process? The simple answer is that survival mechanisms like pheromonal communication, which evolved in the most primitive forms of life, operate below the conscious level. The circuits of our conscious brain are easily swept away by a colorful and powerful vision, whether that vision is of a well-endowed voluptuous female, or a tawny muscular male.Visual input feeds into the optic lobes of our conscious brain where lusty fantasies take over. Distracted by this seemingly irresistible conscious seduction, we are oblivious to the fact that the pheromones from that male or female body have triggered production of GnRH in the hard-wired (unconscious) survival circuits of our brain. We are equally oblivious of the hard­ wired second phase, in which GnRH regulates the production  of LH, FSH, estrogen, and  testosterone. These hormones  circulate throughout the body and brain, firing up our sexual appetite and arousal mechanisms in the conscious brain. Whether we know it, and whether we like it or not, pheromones are a more powerful influence on our behavior than any other type of sensory input. Pheromones affect the hormones that direct our behavior.

Earlier, we explained how odor cues vary with hair color, and with healthy physical features. If we reject the role of pheromonal messengers, there is no comprehensive explanation for the development of personal preferences based on hair color or physical “body” type. Whether you prefer a blond to a brunette, dark skin to light skin, men to women; all these preferences develop as our behavior responds to hormones, while it is also responding to pheromones. In addition, there is no mammalian model that even hints at why we would base any type of sexual behavior on visual input. Sexual behavior is dependent  on  pheromones  in other mammals. Pheromones attract or repel to ensure successful mating. Why would this not be true in humans? 10

SEX DIFFERENCES

Just as our early experiences with food chemistry can alter our food choice later in life, our initial experience with the chemistry of other people-their pheromones, can alter our  mate choice later in life. Current research, for example, tells us, with relative certainty, that a mother’s pheromones alter LH and testosterone levels in infant sons, but not in her infant daughters.The olfactory system of a son reacts to his mother’s pheromones because they come from the “opposite” sex. When the mother’s pheromones induce a change in the infant male’s level of testosterone, and when this change is associated with a pleasurable sensation-a reward, the son’s emotional brain will readily associate that pleas­urable sensation with the pheromones. Again, this association is made automatically, without rising to the level of consciousness. A good example is an experiment involving adding lemon scent to a mother rat’s nipples and vagina. When they grow up, her male offspring will prefer to mate with lemon-scented females.Il

Since, the mother’s breast is the source of pheromones and food, an infant son’s visual response to the breast is readily linked to the effect of her pheromones on his hormones. Psychologists call this a conditioned response.It occurs when one form of sen­ sory input, our sense of smell for instance, affects a response associated with another form of sensory input, in this case, vision. Odor-driven changes in a male infant’s hormone levels condition him to respond with pleasure to the sight of his mother’s breast. What causes this connection? The obvious answer is the effect of the mother’s pheromones on her son’s hormones.l2

Since we know that  human  pheromones influence levels of hormones in other humans, we can now ask how a son’s response to pheromones from his mother’s lactating breast might influence his adult fixation with women’s breasts. After all, a mother’s lac­tating breast appears relatively large.This visual stimulus, coupled with the pheromones from the breast, early in life-will be repeat­ edly associated with the very pleasurable experiences of food, touch, and warmth. That’s why nearly every mother’s son will, as he matures, begin to find large-breasted women more attractive than women with smaller breasts.

In Chapter 6, we suggested an explanation for the development of pendulous breasts in women, which was also based on what we know about pheromones. The pendulous breasts of women are modified scent-producing  glands. Larger breasts contain  more scent glands to secrete more pheromones. Increased pheromone production  means more potent effects on male hormones, like testosterone. Might this scent-testosterone connection also cause males to prefer large-breasted women. Although this multi-tiered explanation is somewhat complicated, biological realities tell us that any visually-based explanation both for breast development, and for attraction  to larger breasts, is not as convincing as our olfactory-based explanation.13

The association between large breasts and sexuality is very basic. One might even describe it as instinctive. It remains in the subconscious mind, only to be demonstrated when the hormones of puberty begin to kick in.l4 Long before the hormones of puberty trigger profound differences in the behavior of adoles­ cent males and  females, pheromones  are triggering hormonal changes in the infant. Good and bad associations, including visual associations, conditioned by pheromones, are being made from birth-even though  they do  not  show up  until  the  onset  of puberty

HUMAN PHEROMONES AND PUBERTY

We also now have evidence that pheromones alter the timing of the onset of puberty in human females. Apparently, the presence or absence of a biological father’s pheromones makes a difference. When the father is present, his daughter does not advance into puberty as quickly as she does when he is not present. 15 If a step­ father or mother’s boyfriend is present, young women advance into puberty faster.16 Other factors like nutrition  also influence the onset of puberty. However, evidence that  exposure to the pheromones of biologically related or unrelated males affects the onset of puberty has been documented in the females of many different species.

For humans, an earlier onset of puberty, coupled with still developing emotional controls, can increase the risk of psychologically premature sexual experiences, unwanted pregnancies, and exposure to sexually transmitted diseases. In other animals, early pregnancy and offspring are linked to survival of the species. To date, we know of no research that explores the impact of human pheromones on earlier puberty and its consequences of earlier sexual intercourse, unwanted pregnancy, abortion, and sexually transmitted diseases.

This absence of research and the likelihood that no researcher will be willing to enter such a sensitive area suggests some specu­lation and some questions that might be worth mentioning here. For instance, what results might we expect if mothers collected pheromones  from  their  daughter’s  biological father, and  used them to delay puberty, in the event that the biological father leaves home prematurely? We might also ask whether it might be wise to begin sex education earlier in families where the father is absent, and especially if a stepfather or mother’s boyfriend is present. Provocative questions like these are very unlikely to be pursued in any clinical test.

Meanwhile, many mothers have reported that maintaining a “bank” of their own pheromones can be helpful with cantankerous infants and young children. Most mothers are aware that placing a article of clothing they have worn in the crib with an infant will help sooth the infant when they are absent. Maternal clothing, or the nesting material of other animals, contains the mother’s natural scent; her pheromones, which play a major role in mother-infant bond. This connection to the scent of one’s mother is crucial for bonding in all mammals.17

Some observers of  human  culture  have suggested that  we humans try to distance our own sexuality from that of animals so that we can continue to delude ourselves that we are somehow different, and therefore superior. We don’t deny that humans are different, and that, typically, we are able to make superior choices. Still, we fail to understand why there is such resistance to recognizing our animalistic heritage, and particularly to recognizing the role that pheromones  and hormones play in our behavior.IS Regardless of this resistance, pheromones  leave their hormonally driven mark on every human born with a sense of smell.

I CAN’T SMELL ANYTHING

What  about  people who are born  with  no sense of smell? If pheromones   are  so  important to  our  sexual lives, we should expect to see some  delay in  puberty  for in  those  who  are not affected by pheromones. Earlier, on  page 59 and  page 167, we mentioned Kallmann’s syndrome, where a gene affects the development  of our reproductive system, our levels of hormones, and our  ability to smell. People with Kallmann’s syndrome  are born with no sense of smell, and experience delayed puberty. Affected males  reportedly  lack interest  in  the  opposite  sex; and  sexual firsts-if any–occur many years later than in people whose sense of smell is functional. Can you imagine how your life might  be changed by an inability to smell?

Our sense of smell plays a primary role in our ability to bond with others, because pheromones alter levels of hormones, like oxytocin, that are linked to these bonds. People with Kallmann’s syndrome have repeatedly reported a failure to bond, and with surprising specifics. For example, several have reported their concern that they did not cry at their mother’s funeral. ”What’s wrong with me?” is a common question.We believe that the lack of the sense of smell and subsequent lack of the bonding between mother and child best explains this commonly reported problem. Unfortunately, we can­ not cite any scientific study that proves this, since this information comes from internet postings and discussions on a listserver for people interested in Kallmann’s syndrome. Nonetheless, we know that the sense of smell is the link that establishes the mother-infant bond in other animals, and that this bond is very important.l9

PHEROMONES AND DESIRE

We also know that people who lose their sense of smell later in life, due to head injury or viral infection, are affected by the loss. Food odors no longer activate the hypothalamus. People who lose their sense of smell tend to gain weight, because no chemical sig­ nal gets through to the hypothalamus to tell their brain they have had enough to eat. More important, sexual desire declines with the loss of the sense of smell in humans, just as it does in other animals. Other animals can be manipulated in experiments to show how much difference their response to pheromones makes in their sexual interest and behavior.20 When people lose their sense of smell, the effect mimics the results of animal experi­ments. With no sense of smell, there are no longer any pheromonal associations on which to base sexual behavior and mate choice; sexual desire declines. Even gradual loss of the sense of smell creates problems. With age, our ability to detect odors declines and so does sexual desire. Smoking cigarettes also reduces our ability to detect odors,21  and has been linked to increased rates of impotence in men.22

PHEROMONES AND TALL MEN

Surges in testosterone levels during  puberty accelerate bone growth and increased density of bones. This is reflected in sex differnces in height and in bone density (e.g., taller men with the stronger  male  jaw). Increased testosterone levels also increase male pheromone  production. So, simply put, taller men with strong  jaws produce more masculine pheromones.23  When women select a tall man, their selection is readily linked to an increase in male pheromone production.

PHEROMONES AND “DARK“ MEN

Women in the ovulatory phase of their menstrual cycle are in the most fertile phase. The fairer skinned of the “fairer sex” have lighter complexions as a result of reduced melanin and hemoglobin levels in the skin’s outer layers. The difference between the male’s darker and the female’s lighter complexion arises at puberty, since sex hormones influence melanin production, hemoglobin levels, and thus, skin color. The production of these sex hormones is also responsible for sex differences in pheromone production. So, keep in mind, ovulatory women prefer the scent of men with darker complexions.24

It makes good pheromonal sense that women who are at the most fertile phase of their menstrual cycle would prefer what is visually perceived to  be a darker  complexion in  males, since darker skin is linked to increased production both of testosterone and of male pheromones. Accordingly, the preference for darker skin is not a visual preference. Rather, it is a subconscious olfac­ tory preference that we attribute to a visual preference. Similarly, the effect tanned  skin may have on visual aspects of physical attraction can be linked with the testosterone-influenced pheromone production in men.

Vitamin D, a steroid hormone activated by light, has been used to correct deficiencies in testosterone in vitamin D-deficient male rats.25 A “good” tan may provide a visual signal of higher testos­ terone levels. At the same time, this visual signal is accompanied by a chemical signal that is linked to higher testosterone levels and increased masculine pheromone output. This may be why natural sun tanning and tanning parlors remain popular, regardless of the associated risk between tanning and skin cancer. Others might argue that tanned skin continues to be viewed as a sign of health and a leisurely lifestyle. So, perhaps it is not merely a pheromone connection that makes darker skin more attractive to women.

PHEROMONES AND HANDSOME MEN

Bilateral symmetry can be described as the equal balance of two halves.26 A line drawn from the middle of your forehead to the middle of your chin, would help to establish the degree to which your face is bilaterally symmetrical. If both sides of the line can be precisely matched, you are perfectly symmetrical, and for whatever reason, symmetry is widely considered attractive. Less of a match, asymmetry, is less attractive. Symmetry is believed to be a visual sign of hormonally determined reproductive fitness, which is basically the testosterone-linked ability to impregnate a woman, or the estrogen-linked ability of a woman to become pregnant.27

Ovulatory women find the scent of symmetrical men most attractive.2B A woman’s ability to detect musky male pheromones also peaks at this stage of her cycle, when she is most fertile. Thus, she is most sensitive to, and responds best to male pheromones that are genetically linked to the development of symmetrical fea­ tures and male reproductive fitness. There is even one report that women have more orgasms when they select men with symmetri­ cal features.29 Orgasm has a  powerful conditioning  effect on future behavior; it will be sought after because of the pleasure associated with the endorphins  produced  during  orgasm. The combination of scent, symmetry, and orgasm helps to reinforce an ovulating woman’s sexual behavior and help her to uncon­ sciously select for the “handsome” pheromones of reproductive fitness when she is most likely to get pregnant.

PHEROMONES AND GENETIC DIVERSITY

Ovulatory women also find the scent of men more attractive when they are most genetically unrelated.30 It is important that all animals select mates who are not closely related. Failure to do so results in inbreeding, which brings increased genetic defects and susceptibility to infections that accumulate and affect the species ability to survive. Species survival depends on the ability of ani­ mals to use their sense of smell to detect extremely subtle differ­ ences in the genetically determined odor of a potential mate. Both men and women can detect these differences, and use this ability to select genetically diverse mates.31 We hinted at this when we reported that children raised in an Israeli kibbutz invariably mar­ ried outside their group, and that the Hutterite women selected men who were the most genetically diverse from those who were available to them for marriage (see pages 137-138). There is now stronger evidence for this claim. Whether this evidence proves beyond any shadow of a doubt  that women use their sense of smell to chose genetically diverse mates is a matter of opinion. However, the evidence shows that women maintain  the ability found in other mammals to select for chemical cues of genetic diversity.32

PHEROMONES AND FEMALE FERTILITY

Men find the scent of women who are near the most fertile stage of the  menstrual  cycle to  be most  attractive.33 When a woman is most fertile (e.g., when she is in the ovulatory phase of her menstrual cycle), her estrogen level reaches its peak. There is evidence that strongly suggests estrogen levels affect the active pheromones she secretes, and that these pheromones also have a profound  effect on levels of testosterone in men. For example, testosterone levels peak 15 minutes after exposure to a chemical mixture, which mimics the natural vaginal odor that is present when a woman is most fertile.34 The result of this testosterone peak is expected to be an increased desire to become sexually active with the fertile female, who is most likely to become preg­ nant as a result.

In other mammalian females, chemical signals alert the male to her readiness for mating and her ovulation.The “bitch in heat”for example sends her chemical signals to male dogs that can pick up her scent from a long distance away and respond with mating overtures. Like other mammalian males, men seem to prefer the scent of a woman who is most fertile.

PHEROMONES AND THE WAIST-TO-HIP RATIO

Men generally prefer women whose body type, specifically, their waist to hip ratio, is linked to fertility. Dividing your hip measurement by your waist measurement provides a waist-to-hip ratio  (WHR)  that  is characteristic of sex differences in  post­ pubertal males and females. An attractive male WHR is 1.0, which when compared to the most attractive female WHR: 0.7, simply reflects that women have a thinner  waist and wider hips than men. This sex difference is primarily the result of sex hormones, and the way that these hormones affect fat distribution. Women tend to distribute fat on their hips; men tend to distribute fat on their mid-section.

Why would a study show that 0.7 is consistently preferred as the most visually attractive WHR of women,35 while 1.0 is pre­ ferred in men? There is no biological basis for the development of this visual preference-unless it is a conditioned response to pheromones.We can fully expect that women with the most desir­ able WHR also emit pheromones linked to the hormones that correlate well with their fat distribution  and with their WHR. These pheromones are the most likely reason women with a 0.7 WHR are more visually appealing to men, and men with a 1.0 WHR are most appealing to women.

PHEROMONES AND SEXUAL ORIENTATION

Currently, sexual orientation  cannot  be explained using the hypothesis that physical attraction is primarily visual. Any expla­ nation of human sexual behavior must account for variations in behavior, like bisexuality and homosexuality. It is not enough, for example, to say that we develop visual preferences that drive our sexual behavior, without  explaining how men become visually attracted to men, and how women become visually attracted to women. Since homosexual attraction  is common  among many mammals, and pheromones drive the sexual behavior of other mammals, it seems more likely that pheromones can better explain homosexuality than any other approach involving visual stimuli.

If the development of a male rat’s sense of smell is altered by a drug that limits sexual differentiation of his olfactory system, as an adult, the male will exhibit bi-sexual behavior.36 The male rat will respond to the odors of a female by mounting her, but he will also respond to the odors of a male by exhibiting a posture that allows him to be mounted.

Homosexual rams respond with increased testosterone to the odors of other males.37 The homosexual rams also have differ­ ences in an olfactory processing center in the brain: the amygdala. Male rats that  exhibit the  posture that  allows other  males to mount them have similar differences in their hypothalamus.38 So do homosexual human  males.39, 40 The hypothalamus and the amygdala are integral parts of the limbic system, the “emotional center” of the human brain. Accordingly, pheromones also may be involved in variations of sexual behavior.

PHEROMONES AND OTHER ATTRACTIVE FEATURES

A colleague who has studied facial beauty was having trouble with  the  concept  of  human  pheromones  and  how  they  are involved with determining what men perceive to be attractive. “I like all women:’he said. First question:”Do you like fat women, or thin women?” His answer indicated a preference for the estrogen component  that  determines body fat distribution.  Estrogen is closely associated with the  pheromones  that  women produce. Second question: “Do  you  prefer blondes, brunettes,  or  red­ heads?” Natural hair color is also linked with both the genetic components of pheromone production and with pheromone dis­ tribution. Brunettes, for example, trap more pheromones in their hair, because their hair is typically thicker than blond hair. The genes that  determine  hair  (and  eye) color are also linked to pheromone production (see pages 159-160).

Our colleague preferred red hair and green eyes.In fact, his first “true love:’and his last three lovers were red-heads, and one even had green eyes.

“What about symmetrical features; the balance that most peo­ple find attractive?” Symmetry also is determined in part by hor­ mones linked to pheromone  production. No answer from the colleague.

“Do  you prefer a woman with broad shoulders, or  narrow shoulders; a strong jaw, or more feminine features like high cheek­ bones and a small jaw?”It didn’t take long for our colleague to dis­ cover that all the features for which he stated a visual preference had connections to women’s differences in genes, hormones, and pheromones. During the course of a weekend conference, he was relatively convinced that he had developed preferences for differ­ ent characteristics of women based on pheromones. Of course, it helped to  convince him  that  his preferences for women were based on pheromones when women’s preferences were explained. Simply put, women prefer tall, dark, and handsome men because these traits are visual signals of fertile masculinity. As we indicated earlier, tall, dark, and handsome is a visual description of a masculine pheromone signature.

A few years later, both Kohl and this colleague were filmed for separate segments of a television special on “Survival of the Prettiest:’ Finally, it seemed that Kohl had an opportunity to tell a large television audience about the role pheromones play in sex­ ual attraction, while also comparing the role of visual input. We waited for the broadcast in anxious anticipation. Francoeur, on the East Coast, was one of the first to learn that Kohl’s interview, filmed in the laboratory, had been left on the cutting room floor. What happened?

The producers substituted a segment on cosmetic surgery, which they felt was more appropriate given the title of the show. Everything else in the show was related to visual aspects of physi­ cal attraction, with no room for our olfactory approach. This is somewhat typical of the mass media approach to human sexual­ity. The olfactory connection is difficult to present on television, which of course is designed for visual stimulation. Besides, some people think the real mysteries of odor in human sexuality are best left unexplained.

Soon after the 1995 release of “The Scent of Eros:’ Kohl was interviewed for an article for Newsweek. Also interviewed were Devendra Singh (of WHR fame) and Randy Thornhill, (of facial symmetry fame). The article was to be entitled “The Biology of Love.” Nothing from the interview with Kohl was included. When asked why, the journalist said his editor realized that the article was so focussed on visual appeal, that anything about olfactory appeal contradicted Newsweek’s approach to the biology of love. We were disappointed, because when it comes to biology, there is no non-olfactory basis for visually perceived physical attraction. That’s why pheromones are more important  than what we see, biologically speaking.

PHEROMONES, NATURAL AND SYNTHETIC

We are frequently asked about  what pheromone-containing product works best to attract the opposite sex. However, evidence of a human pheromone-hormone  connection does not support the marketing claims for the plethora of products that supposedly contain human pheromones guaranteed to attract the other sex. Despite marketing claims that human  pheromones will trigger sexual attraction  and desire in another  person, we are not like other animals. Unlike most animals, most people typically think before they act on some hormonally driven sexual impulse.

At the same time, no one can predict what physical characteristics will be most important to sexual attraction in any other person. Nor can anyone predict what pheromones will be most important  to sexual attraction in another person. These prefer­ ences develop over a lifetime of unpredictable life experiences.

Wearing a pheromone-containing  fragrance is not  likely to “drive women wild” or to make every man “want” you, unless that person has had an sexually-rewarding experience or relationship with a particular  pheromone  or fragrance. The other  person’s reaction and our own are just as likely to be associated negatively as positively, based upon life’s experience. A woman who has been raped, for example, might even find that the natural male scent of a loving spouse triggers her memory of the rape, and repulses her.

Women who learn to love the increased male odor associated with testosterone-charged men in outlaw motorcycle dubs,  are less likely to enjoy a more docile and less odorous man.

DHEA

When human pheromones are discussed at scientific confer­ ences, or  just among friends, the most obvious and frequently asked question is whether we have discovered a human pheromone.  Kohl believes he  has. While others  have experi­ mented with putative human pheromones like androstenone and androstenol, or synthesized chemicals that appear to have genuine effects on others: the “vomeropherins” and the “copulins;’ Kohl has focussed on a different approach.

Any human male pheromone is likely to have a variety of functions. Those that are linked closely to testosterone levels would also be linked to signals of dominance, of attractive physical fea­tures, and  might possibly be used in establishing territory-if only the amount of personal space preferred. Increased production of a male pheromone is also likely to be linked to a rapid response so that when a signal of dominance is required to attract a female, the signal will be manifest quickly, before she walks away. Pheromones linked to testosterone production in the male pig, androstenone and androstenol, are primarily linked to a response cycle that, in men, takes 15 minutes to achieve. To us, 15 minutes means an opportunity lost.

A much quicker response mechanism is required, something akin to the fight or flight response, which is also related to testosterone levels. This kind of near immediate response one finds in the adrenal glands, which we know contribute to pheromone pro­duction in mice.41

The primary adrenal hormone linked to testosterone produc­tion is dehydroepiandrosterone (DHEA). This hormone has been marketed as a human pheromone for use as an additive in a prod­ uct marketed by the Athena Institute, as we mentioned in Chapter 14. A form of DHEA, its sulfate: DHEA-S, ranks second only to cholesterol as the most abundantly produced steroid hormone in men and women.42

Is DHEA, or DHEA-S a human pheromone? For a variety of reasons, this is unlikely. To start with, the levels of DHEA vary lit­ tle between men and women. If DHEA were a human pheromone, it would be hard to imagine how it could effectively signal any particular distinguishing quality of a male, or of a female. Certainly, DHEA would not act as a signal of male hor­mone levels or of female hormone levels. Hormone-related sig­ nals should clearly distinguish a male from a female, and clearly distinguish the menstrual cycle phase of a female. DHEA lacks this sexually dimorphic quality.

When attempting to find a true human pheromone, it is best to take into account the differences between men and women; and, in this case between boys and girls. Pheromone production  in boys and girls begins with maturation of the adrenal glands, slightly before the onset of puberty. Adrenal gland maturation also is linked to the early stages of visible axillary and pubic hair, which help to distribute pheromones. Once the adrenal glands are mature, there also is a sex difference in the productions of the two primary metabolites  of  DHEA: androsterone  (A)  and  etio­cholanolone (E).

Without burdening the reader with the technical details of steroid hormone biochemistry, we need to note that NE ratios are different in men and women. For this reason A may signal mas­culinity, and either lesser concentrations of A, or greater concentrations of E, may signal femininity.

Accordingly, the NE ratio may reflect the degree of masculinity or femininity. More A probably means a higher NE  ratio and more masculine pheromone production. Less A probably means more  feminine  pheromone   production.  The  NE   ratio  also changes in response to fight or flight situations, because the stress hormone: cortisol, suppresses DHEA production. Stressful situa­ tions could lead to a more feminine NE ratio in men due to DHEA suppression. Dominant males who control their environ­ ment are less likely to experience stress than subordinate males who may even be stressed by the presence of other males. Dominant  males are also more likely to have higher NE  ratios that could pheromonally signal their dominance.

Homosexual males are reported to have NE ratios characteris­tic of females. In one experiment, a scientist who measured NE ratios in urine samples was able to predict with 100 percent accu­ racy whether or not the man who submitted the specimen was homosexual.43 This research is particularly interesting because in 1992, just prior to Kohl’s first scientific presentation on this topic, Dr. William G. Turner, an octogenarian psychiatrist, turned geneticist, contacted Kohl. Turner wrote that during the 1950’s, several aging, gay, male patients responded to  his request for information on how they found other gay males. He repeatedly was told: “we smell each other.” During the 1950’s a man who made a mistake about another  man’s sexual orientation  would probably have been lucky if he escaped with a beating. Perhaps the atypical NE ratio, manifest in chemical cues, helped avoid such problems.

Is something like this happening in homosexual rams? Back in 1992, before Kohl’s first presentation to the Society for the Scientific Study of Sexuality, Dr. Anne Perkins was listening to Kohl explain his model to Dr. F. Robert Brush. However, she didn’t listen for very long.She interrupted and said, quite simply: “That’s exactly what’s happening in my sheep:’ Her homosexual rams would approach and sniff the genitals of other males, and exhibit a hormone response characteristic of other rams when they sniffed the genitals of an estrus ewe.

Schizophrenics have unusual DHEA levels when compared to non-schizophrenics.They also produce an odor that has been said to be characteristic of schizophrenia.This odor could be related to their level of DHEA and subsequently their NE ratio. DHEA lev­ els also are linked  to  age-related sexual problems.44 Do  the metabolites of DHEA become pheromonal signals? If so, it may take a few more years of research to prove. It will also take a few more years of research to prove that human pheromones are the primary driving force behind all of human sexual behavior. Meanwhile, Kohl has begun marketing of a product containing androsterone that seems to enhance masculine appeal.

WHY HASN’T ANYONE ELSE TOLD YOU ABOUT THIS?

Researchers have many reasons to avoid discussing topics they consider insignificant, improbable, not worth their time, or sim­ ply something they cannot integrate into their overall scientific picture. When  it comes to  human  behavior, especially sexual behavior, a hypothesis that makes sense can also make for contro­ versy in institutions that require political correctness for funding or other support. It is sometimes as dangerous today, as it was in the days of Charles Darwin, to propose strong links between ani­ mals and humans-especially when it comes to sexual behavior. Professors seeking tenure may be passed over for promotion, lose tenure-track  positions, or be “black-balled, for making claims that are considered too controversial. Right or wrong makes less difference in a politically correct world filled with litigious pitfalls.

Research on the menstrual cycle of women or simply the claim that male pheromones can alter the menstrual cycle and the sexual behavior of women can be twisted into a charge of sexual harassment when it is linked with sexual differences.

Perhaps it is for the best that human sexuality research only be discussed in scientific forums, or in scientific journal articles. Journalists can then interpret this information and reduce its technical content  down  to something  more  people can better understand and talk about. We have seen this happen with the arrival of nearly every new report that mentions human pheromones. And yet, the journalists aren’t telling the whole story, and many people don’t understand.

This does not surprise us, and will not surprise you given a recent report of sex differences in the response to the estrogenic (i.e., female) compound  oestra-1,3,5(10),16-tetraen-3-ol (EST) and the androgenic (i.e., male) compound 4,16-androstadien-3- one (AND). Hypothalamic activation with AND was significantly greater in women, while hypothalamic activation by EST was greater in men. EST induced activity in the olfactory regions of women, while AND induced activity in the olfactory regions of men.45 What, you and the mass media journalists, may ask, does this mean? It means that there is no longer any question about whether human  pheromones exist, and that it is time to fully examine the effects of human pheromones on our behavior.

Kohl was recently enlisted by colleagues from Vienna, to detail the link between pheromones and hormones for publication in a scientific journal. “Human  Pheromones: Linking Neuroendocrinology and Ethology;’ will help other scientists to better understand the link between pheromones and behavior.46

Another recent article links pheromones and male sexual orientation.47 But, as Max Planck indicated in the quote we used to begin this epilogue, it is not  necessarily scientists who will help the majority of people understand the importance of human pheromones. Instead, it is likely that people like you, who have read this book, will help a new generation become familiar with the scientific truth about human pheromones.

The authors of this volume hope that you now have a better understanding of human pheromones and how they influence your life. The picture we have tried to present is like a two-sided coin. One side is the pheromones of others that affect your life.The other side is the effect your pheromones have on the lives of others.

Since we started this epilogue with a quote, it seems fitting to end this update on pheromone research, and its relevance to what we perceive to be visual attraction, to end with another quote borrowed from our first chapter on The Mystery of Odor.

“I should think that we might fairly gauge the future of biolog­ ical science, centuries ahead, by estimating the time it will take to reach a complete comprehensive understanding of odor. It may not seem a profound enough problem to dominate all the life sci­ ences, but it contains, piece by piece, all the mysteries:’ Lewis Thomas48

Notes:

1 In: “The  Structure  of Scientific Revolutions” Third  edition, Thomas S. Kuhn, p. 151, paperback. From Max Planck,”Scientific Autobiography and other Papers’: trans. F. Gaynor (New York, 1949), pp. 33-34.

2 Planck was the  first prominent  physicist to support  Albert

Einstein’s theory of special relativity.

3 Kohl was persuaded by a reviewer to include the question mark at the end of his presentation title, due to the theoretical nature of his presentation.

4 Stern K, McClintock MK {1998). Regulation of ovulation by human pheromones. Nature 392: 177-179.

5 Shinohara K, Morofushi M, Funabashi T, Mitsushima D, Kimura F. (2000). Effects of 5alpha-androst-16-en-3alpha-ol on the pulsatile secretion of luteinizing hormone in human females. Chemical Senses 25: 465-467.

6 Preti G, Wysocki CJ, Barnhart  K, Sonheimer SJ, Leyden JJ, (2001) Male axillary extracts effect lutenizing hormone  (LH) pulsing in female recipients. Poster presentation at the 23rd Association for Chemoreception Sciences Annual Meeting, Sarasota, Florida.

7 Shinohara  K, Morofushi M, Funabashi T, Kimura, F. (2000) Axillary pheromones modulate pulsatile LH secretion in humans. Neuroreport 12: 893-895.

8 Diamond M, Binstock T, Kohl JV. (1996) From fertilization to adult sexual behavior. Hormones and Behavior 30:333-53.

9 Nevertheless, we don’t expect to receive a Nobel Prize. Actually, anyone who became overly familiar with the relationship between pheromones and hormones in other mammals could also have predicted that human pheromones would be the primary sensory influence on human behavior.

10 It is necessary here to move from an animal model to a more specific mammalian model. Otherwise, someone will invariably focus their attention on avian, i.e., bird models of sexual attrac­ tion. This leads to a discussion about the male peacock’s tail being visually attractive to the female-and a number of other examples of how birds use visual characteristics in mate choice. So, in mov­ ing from animal models to mammalian models, we can also simply

say that humans are mammals, we are not birds-and birds are not good models for the behavior of mammals.

11 Fillion TJ, Blass EM (1986). Infantile experience with suckling odors determines adult sexual behavior in male rats. Science 231:

729-31.

12 We know that women react to the pheromones of other women, as is the case with menstrual synchrony, but so far there is no evidence that infant daughters react to the pheromones of their mother. Typically, it is the effect of pheromones from the other sex that increase LH and levels of testosterone in males.

13 There is a popular theory of why the pendulous breasts of women are unique among female mammals. Desmond Morris suggests that pendulous breasts developed to mimic the fleshy buttocks of women, and provide a visual cue of sexual maturation and fertility, as we developed our frontal approach to sexual inter­ course. Again, we see how the focus changes from the effect of pheromones on hormones and behavior, to the effect of visual input, without mention of how visual input affects hormones.

14 So as not to discourage breast feeding by mothers who are appalled that they may be providing sexual stimulation to their infant sons, we note that their infant sons, like infant male rats, have no concept of sexual stimulation. Though most mothers know that infant males exhibit erections that are hormonally driven by increased testosterone (a typical male response to pheromones from the opposite sex), there is no reason to believe that an infant son has sexual thoughts about his mother.

15 Ellis BJ, McFadyen-Ketchum S, Dodge KA, Pettit GS, Bates JE. (1999). Quality of early family relationships and individual differ­ ences in the timing of pubertal maturation in girls: a longitudinal test of an  evolutionary  model. Journal  of Perssonal and  Social Psychology 77: 387-401.

16 Ellis BJ, Garber J. (2000). Psychosocial antecedents of variation in girls’ pubertal timing: maternal depression, stepfather presence, and marital and family stress. Child Development 71:485-501

17 In 1997, after a conference presentation, Kohl met with Mindy Rothstein,  who  had  conceptualized  a “Bonding  Blanket” based upon what she had learned about human pheromones from read­ ing The Scent of Eros.Though it has taken several years for her to bring her new product  to market, we can be relatively sure of its success.

18 Weiderman M. Personal correspondence, Kohl: July 2001.

19 Winberg J, Porter RH (1998). Olfaction and human  neonatal behaviour: clinical implications. Acta Paediatrics 87: 6-10.

20 One recent study showed that anosmic ferrets could not recog­ nize the difference between males and females. Kelliher KR, Baum MJ (2001). Nares occlusion eliminates heterosexual partner selec­ tion without  disrupting  coitus in ferrets of both sexes. Journal of Neuroscience 1;21:5832-40.

21 Frye RE, Schwartz BS, Doty RL (1990) Dose-related effects of cigarette smoking on olfactory function. JAMA 263: 1233-6.

22 Mannino  DM., Klevens RM, Flanders D (1994). Cigarette smoking: An independent risk factor for impotence. American Journal of Epidemiology 140: 1003-1008.

23 When levels of testosterone  are too high, however, maximum height may not be achieved.

24 Frost P. (1994) Preference for darker faces in photographs at different phases of the menstrual cycle: preliminary assessment of

evidence for a hormonal relationship. Perceptual and Motor Skills

79: 507-514.

25  Sonnenberg   J, Luine  VN,  Krey  LC, Christakos  S  (1986)

1,25-dihydroxyvitamin  D3 treatment results in increased  choli­nacetyltransferase activity in specific brain nuclei. Endocrinology 118: 1433-1439.

26 Rikowski A., Grammer K. (1999) Human body odour, symmetry and attractiveness. Proceedings of the Royal Society of London

266: 869-874.

27 Tom Cruise has nearly perfect symmetry in facial features; Lyle Lovett has very asymmetrical facial features.

28 Rikowski A, Grammer  K. (1999) Human body odour, symmetry and attractiveness. Proc R Soc Lond B Biol Sci. 266: 869-74.

29 Thornhill R, Gangestad SW, Comer R. (1995) Human  female orgasm  and  male fluctuating  asymmetry. Animal  Behavior 50: 1601-1615.

30 Wedekind C, Seebeck T, Bettens F, Paepke AJ. (1995) MHC­ dependent  mate preferences in humans. Proc R Soc Lond B. 260: 245-9.

31 Ober C, Weitkamp LR, Cox N, Dytch H, Kostyu DD, Elias S (1997) HLA and  mate choice in  humans. American  Journal  of Human Genetics 61:6-14.

32  Wedekind   C,  Seebeck  T,  Bettens   F,  Paepke  AJ  (1995) MHC-dependent mate preferences in humans. Pro Roy Soc Lond, 260, 1359 (Jun 22), 245-249.

33 Singh D, Bronstad PM. (2001) Female body odour  is a poten­tial cue to ovulation. Proc R Soc Lond B Biol Sci 268: 797-801.

34 Juette A (1995) Weibliche Pheromone- Wirkung  und  Rolle von synthetischen “Kopulinen” bei der versteckten Ovulation  des Menschen. Diplomarbeit an der Universitat Wien.

35 Singh D. (1993) Adaptive significance of female physical attrac­ tiveness: role of  waist-to-hip   ratio. Journal  of  Personality  and Social Psychology 65: 293-307.

36 Bakker J, Baum MJ, & Slob AK (1996) Neonatal inhibition  of brain estrogen synthesis alters adult neural Fos responses to mat­ ing and pheromonal stimulation in the male rat. Neuroscience 74: 251-260.  Neonatal   treatment  with   1,4,5-androstatriene-3,17-dione  (ATD), which blocks the aromatization of T to E, affects sexual differentiation  of olfactory pathways and causes male rats to respond with bi-sexual behavior in the presence of chemosensory stimuli either from females or from other males.

37 Perkins A, Fitzgerald JA, Moss GE (1995) A comparison  ofLH secretion and brain estradiol receptors in heterosexual and homo­ sexual rams and female sheep. Hormones and Behavior 29:31-41.

38 Samama B, Aron C (1989) Changes in estrogen receptors in the mediobasal hypothalamus mediate the facilitory effects exerted by the male’s olfactory cues and progesterone on feminine behavior in the male rat. Journal of Steroid Biochemistry 32: 525-529.

39 LeYay S. (1991)A difference in hypothalamic structure between heterosexual and homosexual men.Science 253: 1034-37.

40 Byne W, Lasco MS, Kemether E, Shinwari A, Edgar MA, Morgello S, Jones LB, Tobet S. (2000). The interstitial nuclei of the human  anterior  hypothalamus:  an investigation of sexual varia­ tion in volume and cell size, number  and density. Brain Research 856:254-8.

41 MaW, Miao Z, Novotny MV (1998) Role of the adrenal gland and adrenal-mediated chemosignals in suppression of estrus in the house  mouse: the lee-boot effect revisited. Biology of Reproduction 59:1317-1320.

42 Davis SR and Burger HG (1996) Androgens and the post­ menopausal woman. J clinical Endocrinol Metab 81:2759-2764

43   Margolese  MS,   Janiger   0.  (1973)   Androsterone-etio­cholanolone ratios in male homosexuals. British Medical Journal 207:207-210.

44 Reiter WJ, Pycha A, Schatzl G, Klingler HC, Mark I, Auterith A, Marberger M. (2000) Serum dehydroepiandrosterone sulfate con­ centrations in men with erectile dysfunction. Urology 55:755-8.

45 Savic I, Berglund H, Gulyas B, Roland P. (2001) Smelling of odorous sex hormone-like compounds causes sex-differentiated hypothalamic activations in humans. Neuron. 31:661-8.

46 Kohl JY, Atzmueller M, Fink B, Grammer K. (2001). Human Pheromones: Integrating Neuroendocrinology and Ethology. Neuroendocrinology Letters 22: 309-321.

47 Kohl, N  (2002) Homosexual Orientation  in Males: Human Pheromones and Neuroscience. The ASCAP Bulletin 3 (2), 19-24.

48 Thomas, L. (1980) Notes of a biology-watcher: On Smell. New England Journal of Medicine 302,13:732.

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