The Scent of Eros 1995 revisited (Chapter 1)

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See first: “A Critical Reassessment of the Anthropogenic CO₂-Global Warming Hypothesis: Empirical Evidence Contradicts IPCC Models and Solar Forcing Assumptions” 3/28/25, reported as: New Study by Grok 3 Beta & Scientists Challenges CO2’s Role In Global Warming 3/28/25 and Scaling plant responses to heat: From molecules to the biosphere 6/12/25

Grok AI consistently fails to link light-activated carbon fixation and the potential of hydrogen (pH) to all biodiversity on Earth via ecological adaptations and our claims in:

THE MYSTERY OF ODOR

For many years, very few scientists expressed an interest in figuring out how we detect odors or in exploring the ways in which the sense of smell might influence human sexual development and behavior. That  situation  has changed radically in the past decade as a few pioneering scientists have made some major breakthroughs  that  have exploded  many assumptions  about  the  relative  unimportance of the sense of smell. This new evidence has revealed some startling connections between the sense of smell and human  sexual development  and behavior–so startling  at times that  as John  Money, director  of the renowned Psychohormonal Research Unit at  the  Johns Hopkins University Medical School, sees it, we are facing what promises to be a veritable explosion of knowledge of how we experience our sexual and erotic  nature. “This  new knowledge will, in all probability, enforce a complete rewrite of the differentiation and development of human sexuality and eroticism early in the twenty,first century.”1

Earlier in this century, a few scientists did in fact recognize the importance of exploring the possible connections  between the sense of smell and sexual behavior. For instance,  eighty years ago, Havelock Ellis, a British psychologist, wrote that “for most mammals not only are all sexual associations mainly olfactory, but the impressions received by this sense suffice to dominate  all others.”2 Ellis found enough evidence that the sense of smell influences human sexual behavior and relationships to fill sixty,eight  pages of fine print  in his classic Studies in the Psychology of Sex: Sexual Selection in Man. “There can be no doubt,” he maintained,  that “the extent  to which olfaction influences the sexual spheres in civilized [sic] man has been much underestimated.”3

Half a century later, Irving Bieber confessed that psychologists had almost totally ignored the role odors and the sense of smell play in human sexual development and in our sexual relationships. He pointed out that this prejudice was not based on a lack of evidence or experiments showing that odors, the sense of smell, and sex have little or no connection. Instead, he laid the blame on a cultural bias that makes research on possible links between the sense of smell and human sexual behavior socially unacceptable. This bias, at least in part, can be traced to our modem obsession with cleanliness and the assumption that a lack of cleanliness causes sexual and other body odors. Bieber maintained that his own extensive observations and reading confirmed Ellis’s contention that “smell is an important component in the total organization of many particular experiences .•. a powerful sexual stimulus.”4

More recently, in the prestigious  New England Journal of Medicine, Lewis Thomas, former president of the Memorial Sloan,Kettering Cancer Center, again focused on the importance of research on the sense of smell. “I should think we might fairly gauge the future of bi logical science, centuries ahead,” he wrote, ”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 sciences, but it contains, piece by piece, all the mysteries.”5

Research in recent years has confirmed  these prophetic insights.

Almost  weekly, experts in different fields of research report new findings documenting how our sense of smell and specific odors influence how we develop as sexual beings, how we find our mates, how and why we bond with certain persons and reject others, and how and why bonds develop between children and family members. Odors influence our choice of persons with whom we have sex, and how often. New research also suggests  that odors influence our learning and memory, our emo, tions and moods. It may well be, as Thomas suggested, that our future progress in understanding odors will be a good indicator of other more sensational and headline,grabbing  discoveries in biology and medicine.

Some casual observations and questions may provide us with initial clues to the possible links between the sense of smell and sex. We will explore these observations later, but for the moment consider the following.6

• Mary Brown and her neighbor have noticed that their daughters menstrual cycles are synchronized with their own cycles, and that all the women in Mary’s office have their period at about the same time.

• Some women have told us they can tell what stage of the menstrual cycle a woman is in by her smell. And many women report experi­ encing an increase in sex drive in the middle of their monthly cycle when they are fertile-the same time some men report finding a woman most alluring.

• What is it about close dancing that makes it an important element in the courtship rituals of many cultures?

• Many women report their sensitivity to the smell of their partner changes during their menstrual cycle, along with the ease with which they reach orgasm.

• Why do many women find the sweaty sports hero or sun-tanned “macho” man so irresistibly sexy?

• Why are some men so strongly attracted to large-breasted women, and might this have anything to do with the scent producing glands in the breasts?

• Why does a sex drive decline in older men and women sometimes coincide with a decline in their sense of smell?

• Does the recently reported increase in the popularity of oral sex owe anything to our emphasis on reducing natural body odors and the difficulty of eliminating natural vaginal odors?

• If variety enhances the spice of one’s sexual life, as folklore suggests, what is it in the novelty of a new partner that is so enticing?

• Does the assumption that blond women have more fun have any­thing to do with male preferences in hair color? And if so, might this be connected with the observation that blondes, brunettes, and redheads smell differently?

• Why do girls and boys report that their odor preferences change after they enter puberty, and what are the sexual consequences of this?

• Why is a reduced sex drive, delayed puberty, and infertility in women often associated with a reduced sense of smell?

• Why does Joanne end up sleeping on her husband’s side of the bed, or wear his shirts or robe while he’s away?

• Why do many children object vehemently when their mothers try to put their security blanket or teddy bear in the wash?

An answer to this last question may well be related to the previous one about why Joanne sleeps on “his” side of the bed and wears his shirt when he is away. The familiar body odors picked up by the child’s blanket or stuffed toy play an important  role in her or his bonding experience and sense of security. Wash a child’s favorite security blanket  or cherished stuffed animal and you remove the familiar body odors associated with emotional  closeness and destroy the feeling of being safe and secure.7 Similarly, the body scent of a lover on the bed, a pillow, or shirt can provide a reassuring subliminal reminder of an absent lover.

Unfortunately, smell is still the least understood of our five senses.

We are just beginning to probe the mysteries of how we smell and what impact odors may have on our development,  our health,  our moods, our behaviors, and even our abstract thought processes.

Part of the problem in talking about how odors may influence our sexual lives is a language problem because these odors do not  fit our usual definition of that  term. When  we talk about odors, we usually think  about  the fragrance of flowers, a vine ripened  melon  or straw berry, or a perfume. Or we think about some repulsive odor that makes us wince at first breath. These odors we consciously recognize because sensory neurons in the nose and our main olfactory system routinely detect and process these odors in conscious circuits of the brain.

But can something have a scent, fragrance, or aroma, that affects us even if we do not consciously detect and identify the odor? Scientists have discovered that some odors are not processed by the main olfactory system. Instead, these chemical messengers are processed subliminally, below the conscious level, in an accessory or secondary olfactory system.8 This second kind of chemical signal, known as a pheromone, is defined by Webster’s  Unabridged  Dictianary of the English Language  as “any of a class of hormonal  substances secreted by an individual and stimulating a physiological or behavioml response from an individual of the  same species.” Pheromones are chemical  messengers, odors that convey  information  subliminally between  two or more individuals of the same species. Because some pheromones  affect sexual behaviors, they are sometimes  referred to as sex attractants, even  though  most pheromones do not affect sexual behavior.

But if pheromones opemte below the level of conscious perception, should we refer to them as odors or scents? The dictionary defines an odor as “that property of a substance which  affects  the  sense  of smell.” Pheromones are detected by the accessory olfactory system in warm blooded animals, so apparently they do qualify as odors, smells, and scents.

We also have considerable evidence that pheromones affect humans although  we do not  understand  the anatomy  behind  their detection.

Hence the title of our book, The Scent of Eros: Mysteries of Odors in Human Sexuality. Because our focus is on pheromones that affect our hormone levels, the development of our brains, and many of our sexual behaviors, we will refer to these subliminal chemical signals as scents or odors.

How HUMAN  ARE WE?

Immanuel Kant,  whose effort to define  precisely  the  superiority of humans  is a landmark  in Western  thought,  constantly deplored  any suggestion that noble humans could be influenced by anything so base or animalistic as odors. For Kant, smell was “the most dispensable and ungrateful  of all the  senses.” To suggest that  odors  might  influence human emotions and behaviors, he claimed, would be to deny human free will. Being human meant being fully conscious and above the kind of gross, reflex reactions animals experience.9

Obviously, we disagree and find Kant’s assumption totally illogical. To begin with, Kant assumed that humans have only one mind, a con, scious, thinking, analytical-soft,wired in computerese-brain with the freedom of choice lower animals cannot experience. He ignored the possibility that the brains or minds other animals use to process and react to information from their bodies and surrounding environment  might persist and comfortably coexist with the conscious brain and free will unique in humans. In all animals with internal  skeletons, including humans, odors influence the hard,wired mind of the brain stem or reptilian brain and the emotional circuits of our limbic mind. While they operate below the level of consciousness, the reptilian and limbic minds control  our life,sustaining reflexes of feeding, fighting, fleeing, and mating.

The presence of these ancient minds  and  their behavioral responses is as much a part of human nature as is the very sophisticated conscious brain sitting on top of them. Without  such primitive triggers as touch, taste, and smell sparking our automatic, hard,wired behaviors and  emotions,  we would be disembodied spirits, not  humans  able to adapt  to rapid changes  in our environment without  wasting time  to analyze the situation  and weigh our options. In fact, humans have rep, tilian, limbic, and conscious brains that work together  to make us the unique creatures we are. 10

Kant is also wrong because he spoke as an armchair philosopher who never bothered to test his theory against reality with scientific experimentation. When  a scientist thinks about odors and their possi, ble effects on humans, she or he starts by asking a question. The question becomes a hypothesis that  can be tested experimentally. Looking at the experimental findings we will discuss later, we arrive at the position that Kant was totally wrong: odors do very much influence human sexual development  and behavior. Of course, the ramifications of this broad conclusion  are obvious in the kinds of questions scientists have asked themselves as they pursued the idea that odors play a role in our sexual lives.

Are  human  hormones  broken down  into  pheromones  the same way pheromones  are produced by dogs, bulls, cows, and other  mammals? Are the effects of these subliminal odors on sexual development and  behaviors  in any way similar in humans  and other  animals? Do pheromones influence the way our genes work? Do they affect production of the hormones  that  direct and control  our sexual development and behavior? Are neural pathways in the brains of men and women affected differently by the same pheromone? Do gender differences in these reactions result in different messages being sent from the  brain back to the body for translation  into sexual behavior? Do pheromones affect the primitive, emotional  circuits of our brains? Do some pheromones play important  roles in our emotion-laden sexual behavior and relationships? Do odors affect learning and memory?

One reason why a “yes” answer to any of these question would not surprise a biologist is that biologists operate on the tested premise that biological processes are usually fairly consistent from one species to the next, even  though  there are often  tremendous differences. One  basic element  in this consistency is that  we share similar genes that  deter, mine the structure of enzymes, hormones, receptors, and other proteins that  determine  the anatomical  structures and physiological processes we share with other animals.Thus  it is reasonable to assume that, if the sexual behavior  of other  animals  is influenced by the chemical  mes, sages in odors  and  the  sense of smell,  then  our own  human sexual development and behavior might be similarly influenced by the subliminal odors we call pheromones.

Not long ago it was widely held that what made humans uniquely human was our ability to make tools, think abstractly, and talk. We now

know that we share tool,making abilities with other animals, especially chimpanzees and apes. Other animals besides humans can and do show altruism, courage, intelligence, invention, curiosity, and forethought, as well as friendship, love, fidelity, and many other characteristics once thought to be uniquely human. Dolphins, whales, chimpanzees, and other mammals cannot challenge our verbal skills, but they do have some fairly sophisticated ways of communicating.

If we look for absolute differences between us and other mammals, no clear  distinguishing characteristics for our species  emerge. Differences do exist, but they appear to be relative or quantitative rather than qualitative and essentiaL

In defense of human uniqueness, some deny our “animal” nature altogether and try to create a solid wall between animals and humans. The mythic creation story of Genesis, for instance, draws a clear dis, tinction by giving man dominion over all the animals. Some philoso, phers, psychologists, and scientists attempt to put as much distance as possible between us and our animal origins, downplaying the fact that we share 98 percent of our genes with other higher primates. That 98 percent of our genes we share with our closely related animal relatives makes some similarities and connections between animal and human behavior unavoidable and undeniable.

Even though human sexual interactions are much more complex than the mating of other animals because we can mix love with hor, mone,driven lust, this does not  mean that  factors like odors and pheromones that influence the mating of other warm,blooded animals no longer function in humans. In the brains of the earliest land animals, the olfactory system became intimately associated with mating and reproduction, and those early connections between odors and sex have persisted even as brains became more and more complex and conscious.

In the higher primates and among humans, the sexual drive and sexual behavior are no longer limited to reproduction. Humans have added pleasure, recreation, playfulness, exploration, curiosity, and love to the expression of our sexuality, even though we still talk about bio, logical clocks ticking away in women and our genes being driven to perpetuate themselves.

With or without contraceptives, we know that humans around the world increasingly engage in sex for reasons other  than  making babies. The World Health Organization estimates that in one day, two hundred million men and women around the globe engage in vaginal intercourse. Less than a million of these sexual unions result in preg­nancies, so obviously reproduction is not the main motive for human matings. In terms of species survival, humans are far less efficient in their matings than  other  mammals where the female periodically comes into sexual heat and is receptive to mating only when she is fer­ tile and likely to become pregnant. On average, two humans copulate a hundred times to produce a single pregnancy. (This does not take into account the time and energy humans invest in self-pleasuring, oral sex, and other non-coital erotic pursuits.)

The “World Health Organization Score Board” clearly shows plea­sure/play winning  over baby-making, by a score of 99,090,000  to 910,000! With easier-to-use, more effective contraceptives coming on the market and growing concern about overpopulation and AIDS, the score is likely to be even more lopsided in the near future.11 But admit­ ting that humans increasingly engage in sex for pleasure, recreation, bonding, or love far more often than we do to make babies does not mean that odors and pheromones no longer influence our sexual behavior and pairbonding.

Claims of human uniqueness and moral superiority are in fact based on social designs custom-made by humans who assume that our human sexual behavior has transcended the primitive, animalistic drives of the lower animals. The fallacy of the moral superiority assumption is revealed by scientific evidence that odors may, as we will see, activate genes in the neurons that regulate the cycles of human sex-hormone production, which in turn strongly affect our sexual behavior, regardless of conscious motives like tension  release, sensual pleasure, mutual desire, love, or reproduction.

THE CONSISTENCY OF LIFE

Biological science is based on the assumption that a basic logic and effi­ cient  consistency pervades the way all living organisms, from one­ celled animals to humans, have developed to carry on the processes of living. Biological logic tells us that  the information encoded in the functional  units of DNA  (deoxyribonucleic  acid) we call genes is responsible for both the similarities and the differences we find among individual humans and between humans and other primates.

Specific genes are responsible for the structures and processes that produce hormones in animals and humans. Some of the hormones produced by primates and our four-legged distant cousins are so similar we can use animal hormones to remedy a hormone deficiency in humans. The final link in the chain is the fact that hormones clearly influence behavior (including sexual behavior) in the lower animals, in mam­ mals, in primates, and in humans.

This evidence cuts across many traditional disciplines. In the past, geneticists, endocrinologists, embryologists, psychologists, anthropolo­gists, and others pursued their questions and tested their hypotheses about possible connections between odors and sex in their own narrow discipline. Today we know the questions and hypotheses are so complex that it will take more than the discipline-bound scientists working on their own to make real breakthroughs.

We need a new science that brings different specialists together in a team approach. The new science, known as psychoneuroendocrinology, is already born and growing like any healthy, robust infant. Ten syllables and twenty-four letters is impressive, but hardly indicative of the  creative minds  that  this  new approach  brings together. The strength of this new science is its integration: psycho–for “behavior”; neuro–for “nerve cells,” the nervous system and the brain; endocrin­ for “hormones” and the genes that direct their production; and ology­ for “the study of.” There you have it, psycho-neuro-endocrin-ology, the study of how hormones affect the nerve cells that affect behavior.

Before we go any further, we need to clarify the concept of a hor­mone. Hormones  are chemical  messengers secreted  by ductless or endocrine glands, like the pituitary, ovaries, and testes. Hormones circu­ late in the blood and are picked up by receptors in the target cells where they control gene activity, cell processes, and development.12

In psychoneuroendocrinology, the logic of cause-effect, “this” produces “that,” is not always a straight line. One gene can have several different effects, just as a single hormone like testosterone or estrogen can have many different effects in different organs of the body.13 The relationships between genes, nerve cells, hormones, and behavior, espe­ cially the sexual behaviors of humans involved in bonding, love, com­ mitment, altruism,  and spirituality,  are more complicated than  a simple, single linear cause-to-effect. In this new science, we are dealing with many causes–odors, genes, hormones, and neuralcircuits-interacting together to produce several different effects and behaviors, at different times, in different degrees, and in different parts of the brain. This is a major, but not insurmountable, problem for psychoneuroendocrinologists.14

While psychoneuroendocrinologists cannot experiment directly on humans by manipulating their genes and hormones, they can often find evidence in animal research that suggests tentative,  cautious insights and theories about humans. Animal studies can never account for all of human variability, but evidence from animal studies can provide new insights into possible parallel or similar links between odors, genes, nerve cells, hormones, and behavior in humans.

In many species of animals, odors are produced and detected by males and females in ways that clearly influence their courtship, mating, and parenting behaviors, as well as the social structure and interac, tion of individuals in the family, hive, colony, or herd. We know a good deal about these effects on animal behavior, but we are just beginning to understand how odors influence human sexual behavior. We have many bits and pieces of research with animals, and some with humans, that fit together and suggest a big picture that is biologically consistent but also allows for important differences between different animal species, and between other animals and humans.

Here, biological consistency suggests we jump,cut to a connection between odors and the immune system that makes us the unique individuals we are. Early in the research on organ transplants, scientists learned that all cells carry a unique protein signature on their surface that enables a donor’s immune system to identify and reject a trans, planted organ. These identifying protein tags are produced by a group of genes located in a region known as MHC or Major Histocompatible Complex. But the MHC genes are also responsible for the distinctive body odor litter,mates share in common. This identifying body odor enables a mouse to quickly tell whether an approaching mouse is a fam, ily member or potential enemy that needs to be driven off.15 “One of the most exciting recent developments in the study of individual odors is the finding that several primate species, including humans, may have the ability to distinguish between individuals by [their] odors.”16 Yes. some humans can apparently tell whether two mice come from the same litter or from different strains based on the identifying odor of their urine and feces.17 In a similar way, dogs can discriminate between the smell of garments worn by non,identical twins, but cannot detect a difference when the garments were worn by identical twins.18 In all animals, the many different systems work together so that the sense of smell and the unique identifying odors a body produces are part of the whole system, and connected more or less with their survival and sexual behavior.

In addition to the obvious survival advantage this ability gives a mouse when it is approached by a potential enemy, this ability to detect body odor gives mice another advantage. Biologists have long known that inbreeding-mating between closely related males and females-increases the risk of severe, often lethal conditions in the off, spring. If an individual happens to have a single defective gene, she or he will not show its effects provided the gene is “recessive” and requires two copies to be expressed. A person with one defective recessive gene will be normal but can pass the defective gene on to an offspring, who will also be normal provided it does not receive a matching recessive gene from the other parent. Unfortunately, when both parents are closely related, their offspring is more likely to receive the same defective gene from each parent and to suffer serious consequences.

Some ten thousand years ago our distant ancestors discovered this aspect of sexual reproduction when they started capturing and keeping wild animals as livestock. Breeding these animals to produce more docile beasts of burden, more wool or milk, and better hunting and guard dogs quickly became a major preoccupation. Smart breeders observed the advantages and risks of inbreeding close relatives and out, breeding with a stud or prize female in a neighboring herd. Shared observations produced a hypothesis, a theory, and finally, a conclusion. They could test this conclusion by carefully comparing the offspring produced by breeding closely related and unrelated males and females.

Anthropologists, following the lead of Claude Levi,Strauss, do not believe this understanding of the genetics of breeding cattle, sheep, and dogs played a significant role in the origins of human taboos against incest. For many anthropologists like Levi,Strauss, social rules about marriage are what makes us different from other animals. These regulations determine who officially mates with whom and they appear to be more designed to reduce kinship conflicts and to promote the exchange of women between male lineages.

Wild animals, mice, dogs, and cats do not have the ability to create a hypothesis about the risks of their breeding with close kin. And yet, given a choice, most animals in the wild will not mate with litter,mates. Why? Mice appear to have some kind of neural program for recognizing odors that allows them to welcome litter,mates and respond to a strange odor by attacking an outsider. While the ability to distinguish litter,mates from non,litter,mates by their  odors triggers clan  bonding  and  nest defense, it also seems to trigger a negative reaction, based on the same odors, that prompts them to avoid mating with a familiar,smelling litter, mate while being attracted to the unfamiliar odor of unrelated mice. Both behaviors obviously -promote survival for mice and other  animals that share similar odor,based mechanisms for recognizing kin and stranger.

And  what about humans? Closely related humans grow up more or less sharing the same home space for many years. Family members also share  very similar MHC  genes, and  a daily familiarity  with  the unique  odor  associated  with  those shared  genes. Given  the  harmful effects of inbreeding and the benefits of diverse genes that come with marrying outsiders, the logic of biological systems might favor develop, ment  of emotional and  mating  circuits  in our  brains  that  promote bonding with familiar,smelling kin, and falling in love and mating with the different,smelling stranger. Basing such tendencies on the interne, tions of our genes, sense of smell, and neural circuits would be efficient and could improve our genetic health.

TESTING THE FLAME

Jump,cut for a minute from this discussion about odors and incest to testing this hypothesis.

Whether we are talking about how odors influence human behavior, or about the role black holes played in the origins of our universe, we do know that all of our knowledge is conditional. We are constantly expanding, revising, redrawing, and  updating  our pictures of human behavior. An incurable curiosity drives us to an endless search for better answers to questions that are never quite answered to our satisfaction.

A major problem in this endless quest for understanding is the difficulty we have in proving that a particular event or behavior-“this”-is caused by some other particular factor-“that.” We build our picture of how  things  in our  world function on  a scaffold  of ideas,  theories, hypotheses, and laws designed to connect the “this’s” and “that’s” of our world into a meaningful structure. If these connections make sense, and if our evidence supports the different conclusions, we can fit the different hypotheses together into a bigger picture that makes sense of our world. And that is what all science and human wisdom is about, trying to make sense of the incredibly complex and confusing world we live in.

A hypothesis may start out as nothing more than a guess, a mere idea. Or we may tease it out of exquisitely detailed scientific experiments. Whatever its origins, a scientific hypothesis stands or falls on logic and on the strength of the evidence we gather to justify calling this idea an observation, a hypothesis, a theory, or eventually a law of nature.19   In this knowledge system, the logic of evidence and the way we prove something are independent of where we get our original idea. Whether  or not one has been educated as a scientist, the important thing  is to ask logical, analytical  questions  about  the connection between “this” and “that.”

The first time a child puts a hand into an open flame and finds out what “hot” or “bum” means, he or she is well on the way to forming a hypothesis about the connection between cause and effect, in this case, between the flame and pain. The child may need more than one simi larly painful experiences before she or he realizes that the cause and effect connection is more than just a hypothesis, and that some kind of law of nature comes into play when flame contacts skin.

This  is how the  painful observation that  a flame bums  was expanded into a law of nature that includes burns from all hot surfaces, electromagnetic radiation, X,rays, and sunlight. But the scientific venture also requires that scientists constantly test and challenge what is considered a biological law or law of nature.

A WORKING HYPOTIIESIS

In other animals, odors are a major factor in the interactions between genes, nerve cells, hormones, and neural pathways during development. Odors also affect the circuits and pathways within the brain that influence learning, memory, and behavior. Since humans share many of their biological systems with other animal species because we are animals, it seems logical that odors and the sense of smell probably play a much greater role than we commonly think in human social interactions, sexual attraction, sexual arousal, mating, bonding, and parenting.

Briefly stated, this is the hypothesis we propose to examine in this book.

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