Human pheromones and sexual attraction

Unlocking the psycho-social-dermal axis: A double blinded randomized placebo controlled study unveiling the influence of a novel topical formulation on skin quality, attractiveness, quality of life, and sexual satisfaction

BACKGROUND

Improved skin appearance is closely linked to higher self-esteem, favorable first impressions, and enhanced quality of life, with skincare products often being formulated with biostimulatory and regenerative ingredients to both enhance skin health and provide psychological benefits. Certain components, such as phospholipids and botanicals, may not only improve skin quality, but also impact mood, romantic bonding, and sexual attraction.

AIMS

To assess whether a novel topical skin care product formulated with a proprietary combination of proteins, lipids, and botanical derivatives, can potentially result in a robust psycho-social-dermatological benefit via modulation epidermal oxytocin and pheromonal pathways.

PATIENTS/METHODS

In this single-center prospective, randomized, controlled, double-blinded study, 40 female subjects were randomly assigned to use of either active novel skincare products, or placebos, for 4-8 weeks. Skin assessments, standardized photography, first impression ratings, and questionnaires on confidence and sexual satisfaction were conducted.

RESULTS

Thirty-nine subjects completed the study and demonstrated a statistically significant improvement in skin quality following 4 and 8 weeks of use, with improvements of greater magnitude demonstrated with a longer duration of use. Product users projected a better first impression and appeared on average 3 years younger than their actual age, with 86% of subjects reporting increased confidence. Product users found random people of the opposite sex to be more attractive 88% of the time and reported improvement in sexual satisfaction in 90% of the categories.

CONCLUSIONS

The use of this novel topical product culminated in statistically significant improvements in skin quality, confidence, sexual relationship satisfaction, perceived attractiveness, and youthfulness, highlighting its potential in anti-aging and mood enhancement.

Complexity of Chemical Emissions Increases Concurrently with Sexual Maturity in Heliconius Butterflies

Pheromone communication is widespread among animals. Since it is often involved in mate choice, pheromone production is often tightly controlled. Although male sex pheromones (MSPs) and anti-aphrodisiacs have been studied in some Heliconius butterfly species, little is known about the factors affecting their production and release in these long-lived butterflies. Here, we investigate the effect of post-eclosion age on chemical blends from pheromone-emitting tissues in Heliconius atthis and Heliconius charithonia, exhibiting respectively free-mating and pupal-mating strategies that are hypothesised to differently affect the timing of their pheromone emissions. We focus on two different tissues: the wing androconia, responsible for MSPs used in courtship, and the genital tip, the production site for anti-aphrodisiac pheromones that affect post-mating behaviour. Gas chromatography-mass spectrometric analysis of tissue extracts from virgin males and females of both species from day 0 to 8 post-eclosion demonstrates the following. Some ubiquitous fatty acid precursors are already detectable at day 0. The complexity of the chemical blends increases with age regardless of tissue or sex. No obvious difference in the time course of blend production was evident between the two species, but female tissues in H. charithonia were more affected by age than in H. atthis. We suggest that compounds unique to male androconia and genitals and whose amount increases with age are potential candidates for future investigation into their roles as pheromones. While this analysis revealed some of the complexity in Heliconius chemical ecology, the effects of other factors, such as the time of day, remain unknown.

Maintaining vulvar, vaginal and perineal health: Clinical considerations

Knowledge of female genital anatomy and physiology is often inadequate or incorrect among women. Precise patient-physician conversations can be inhibited by a reluctance or inability to speak accurately about the vulva and vagina, with the terms often being used interchangeably. There is a paucity of scientific evidence and clinical guidelines to support women and physicians in ensuring best practices in feminine hygiene. In this review, the unmet needs in the field are highlighted. Evidence is provided for the complex array of physiological and pathological systems, mechanisms and behaviours that either protect or, if inappropriate, predispose the vulva and vagina to infections, irritation or other conditions. The need for attention to perineal health is recommended, given the interdependence of perineal and vulvar microbiota and the risk of colonic pathogens reaching the vulva and the vagina. Differences in feminine hygiene practices can vary widely across the world and among varying age groups, and suboptimal habits (such as vaginal douching or the use of certain cleansers) can be associated with increased risks of vulvar and vaginal conditions. Critical areas for discussion when advising women on their intimate health include: advice surrounding aesthetic vulvar cosmetic trends (such as depilation and genital cosmetic surgery), bowel health and habits, and protection against sexually transmitted infections. Routine, once-daily (maximum twice-daily) washing of the vulva with a pH-balanced, mild cleanser is optimal, ideally soon after bowel voiding, when feasible. Due to the finely balanced ecosystems of the vulva, the vagina and the perineal area, a scientific and clinical perspective is essential when determining the most appropriate vulvar cleansers based on their components. Correct intimate care may contribute to improved genital and sexual health and overall well-being. An increased awareness of correct practices will empower women to be the advocates of their own intimate health.

Recognition of Gonadal Development in Eriocheir sinensis Based on the Impulse of Love at First Sight

Given the difficulty in identifying individuals with different degrees of ovarian development, we developed a new device utilizing the hypothesis of mutual attraction behavior between male and female crabs with mature gonads by releasing the sexual pheromone so they could be examined. From a total of 40 female crabs, 10 were isolated within half an hour. Histological analysis showed that the ovaries of crabs in the isolated group were in stage IV, while those of the control groups were in stage III. In addition, progesterone (PROG) in experimental groups was significantly reduced compared with the control group (p < 0.05), but no significant difference was detected in estradiol (E2). In response to the different developmental stages, hemolymph biochemical indices and the determination of gonadal fatty acids profiles were explored. The results indicated only C18:4 showed a significant difference between these two groups. A transcriptome was generated to determine the genes involved in the mutual attraction process; differentially expressed genes (DEGs) were significantly related to gonadal development. Therefore, the device can be used to isolate Chinese mitten crabs with stage IV ovarian development.

Judgements of attractiveness of the opposite sex and nostril differences in self-rated mood: The effects of androstenol

Androstenol has been reported to influence judgements of attractiveness and to affect participants' mood. In the present study, participants were asked to sniff androstenol or a control odour (pure ethanol) unilaterally with the left or right nostril. Subsequently, they rated the attractiveness of photographs of the opposite sex and their own feelings on four mood scales. Participants rated the photographs as significantly more attractive after sniffing androstenol compared with the control odour. This did not depend upon androstenol being perceived as pleasant. Androstenol made male participants feel more lively, and both male and female participants more sexy, when sniffed through the right compared with the left nostril. Participants rated themselves as more irritable and aggressive when exposed to androstenol through the left nostril. The findings are discussed in relation to the effects of arousal on attraction and in the context of current theories of hemispheric differences in emotion.

Phenomenological and existential contributions to the study of erectile dysfunction

The current medical approach to erectile dysfunction (ED) consists of physiological, psychological and social components. This paper proposes an additional framework for thinking about ED based on phenomenology, by focusing on the theory of sexual projection. This framework will be complementary to the current medical approach to ED. Our phenomenological analysis of ED provides philosophical depth and illuminates overlooked aspects in the study of ED. Mainly by appealing to Merleau-Ponty's Phenomenology of Perception, we suggest considering an additional etiology of ED in terms of a weakening of a function of sexual projection. We argue that sexual projection can be problematized through cognitive interferences, changes in the 'intentional arc', and modifications in the subject's 'body schema'. Our approach further highlights the importance of considering the 'existential situation' of patients with ED. We close by reflecting briefly on some of the implications of this phenomenological framework for diagnosis and treatment of ED.

The major evolutionary transitions and codes of life

Major evolutionary transitions as well as the evolution of codes of life are key elements in macroevolution which are characterized by increase in complexity Major evolutionary transitions ensues by a transition in individuality and by the evolution of a novel mode of using, transmitting or storing information. Here is where codes of life enter the picture: they are arbitrary mappings between different (mostly) molecular species. This flexibility allows information to be employed in a variety of ways, which can fuel evolutionary innovation. The collation of the list of major evolutionary transitions and the list of codes of life show a clear pattern: codes evolved prior to a major evolutionary transition and then played roles in the transition and/or in the transformation of the new individual. The evolution of a new code of life is in itself not a major evolutionary transition but allow major evolutionary transitions to happen. This could help us to identify new organic codes.

Interpersonal Chemistry: What Is It, How Does It Emerge, and How Does It Operate?

Although chemistry is a well-known, sought-after interpersonal phenomenon, it has remained relatively unexplored in the psychological literature. The purpose of this article is to begin articulating a theoretically grounded and precise definition of interpersonal chemistry. To that end, we propose a conceptual model of interpersonal chemistry centered around the notion that when two or more individuals experience chemistry with one another, they experience their interaction as something more than the sum of their separate contributions. Our model stipulates that chemistry encompasses both behavior (i.e., what chemistry "looks like") and its perception (i.e., what it "feels like"). The behavior involves interaction sequences in which synchronicity is high and in which people's goals are expressed and responded to in supportive and encouraging ways. The perception of chemistry includes cognitive (i.e., perception of shared identity), affective (i.e., positive affect and attraction), and behavioral (i.e., perceived goal-relevant coordination) components. We review existing research on chemistry as well as supporting evidence from relevant topics (e.g., attraction, similarity, perceived partner responsiveness, synchrony) that inform and support this model. We hope that this conceptual model stimulates research to identify the circumstances in which chemistry arises and the processes by which it affects individuals, their interactions, and their relationships.

The Role of Fatty Acid Metabolites in Vaginal Health and Disease: Application to Candidiasis

Although the vast majority of women encounters at least one vaginal infection during their life, the amount of microbiome-related research performed in this area lags behind compared to alternative niches such as the intestinal tract. As a result, effective means of diagnosis and treatment, especially of recurrent infections, are limited. The role of the metabolome in vaginal health is largely elusive. It has been shown that lactate produced by the numerous lactobacilli present promotes health by limiting the chance of infection. Short chain fatty acids (SCFA) have been mainly linked to dysbiosis, although the causality of this relationship is still under debate. In this review, we aim to bring together information on the role of the vaginal metabolome and microbiome in infections caused by Candida. Vulvovaginal candidiasis affects near to 70% of all women at least once in their life with a significant proportion of women suffering from the recurrent variant. We assess the role of fatty acid metabolites, mainly SCFA and lactate, in onset of infection and virulence of the fungal pathogen. In addition, we pinpoint where lack of research limits our understanding of the molecular processes involved and restricts the possibility of developing novel treatment strategies.

Neuroenhancement: State of the Art and Future Perspectives

Pharmacological neuroenhancement refers to the non-medical use of prescription drugs, alcohol, illegal drugs, or the so-called soft enhancers for the purpose of improving cognition, mood, pro-social behavior, or work and academic performance. This phenomenon is undoubtedly more frequent than previously supposed especially amongst university students. The aim of the present paper was to carefully review and comment on the available literature on neuroenhancement, according to Prisma guidelines. The results showed a great use of all prescribed drugs (benzodiazepines, antidepressants, antipsychotics, nootropic compounds, and especially stimulants) as neuroenhancers amongst healthy subjects, although probably the real prevalence is underestimated. The use of illicit drugs and soft enhancers is similarly quite common. Data on the improvement of cognition by other compounds, such as oxytocin and pheromones, or non-pharmacological techniques, specifically deep brain stimulation and transcranial magnetic stimulation, are still limited. In any case, if it is true that human beings are embedded by the desire to overcome the limits of their intrinsic nature, neuroenhancement practices put into question the concept of authenticity. Therefore, the problem appears quite complex and requires to be deepened and analyzed with no prejudice, although within an ethical conceptual frame.

Prior exposure to Hedione, a model of pheromone, does not affect female ratings of male facial attractiveness or likeability

The existence of pheromones in humans is controversial, partly because of definitional difficulties and partly because of the question of possible chemical substances. The synthetic compound Methyl dihydrojasmonate (Hedione) is potent to bind to vomeronasal-type 1 receptors (VN1R1s) and activate limbic areas of the brain in a sex-specific manner. However, one of the most important definitional points for a human pheromone effect has not yet been investigated, i.e., whether smelling Hedione, a model of pheromone, has a behavioral effect. We tested in females whether Hedione leads to altered perception of male social stimuli. Each of the included women were sensitive to Hedione and were tested around the time of ovulation in three consecutive sessions, during each they were exposed to either Hedione or Phenylethyl alcohol or Odorless air. We measured the speed of male face recognition (implicit priming task) and collected ratings of facial attractiveness and likeability of men (explicit task). Only about half of the women tested were sensitive to Hedione. Those women did not show any effect of Hedione exposure in the implicit priming task and moderate, but non-significant effects in the explicit task. We therefore assume that Hedione is not a potent model of pheromone in humans and this observation may be due to the fact that the artificially produced substance is not suited for signaling the proximity of other humans. Furthermore, the high rate of Hedione-specific anosmia leads to the hypothesis that a substantial proportion of individuals has a poor V1NR1 receptor expression.

The Effect of Female Pheromone on the Functional State of Young Men

Introduction. Modern studies show that the presentation of smell of female mice before male mice infection with the influenza virus activates non-specific immune response which protects male mice from infection of the upper respiratory tract and reducing their mortality. However the researches have not studied the adaptive effect of female sexual pheromone on men.

The aim of this work was to study the effect of odor of synthetic analogue of natural female pheromone (Osmopherine) on the functional state of young men often suffering from acute respiratory infections (ARI) and allergic diseases.

Materials and methods. We studied four-week effect of Osmopherine on the psycho-emotional state, the concentration of hormones (testosterone, cortisol) and immunoglobulins (sIgA, total IgG), the percentage of leukocytes in the blood and the individual smell of young men, who have ARI more than 4 times a year or an allergic disease. The study involved 117 boys aged 19–23 years. Olfactory testing of individual odor samples of young men was carried out by young women (n = 32) aged 18–22 years.

Results. It was found that female pheromone has a positive effect on the functional state of men with different immune systems. However its effect is caused by the pathogenesis of the disease. Application of Osmopherine in men with reduced immunity causes an increased activity, improved mood, reduced anxiety and stabilized testosterone level. Men with allergic diseases did not have the same effect. A significant 2 times decrease in the content of eosinophils was found, which indirectly indicates the decrease in the activity of the delayed phase of allergic reactions of immediate type.

Conclusion. The immune system functions according to its internal laws and programs. However its activity for the benefit of the whole body is integrated and regulated by the nervous and endocrine systems. Therefore modulating effect on the functioning of the immune system can be mediated through the presentation of pheromones.

Steroidal pheromones and their potential target sites in the vomeronasal organ

Steroids are important olfactory signals in most mammalian species. The vomeronasal organ has been suspected to be the primary target of pheromones. In rat vomeronasal sensory neurons express steroid binding proteins and nuclear receptors. Some binding globulins were found also in single ciliated cells of the non-sensory vomeronasal epithelium. Immunoelectron microscopy revealed VDR in olfactory microvilli and DPB in apical membrane protrusions of supporting sells within the sensory epithelium. Pilot behavioral studies with dogs showed increased sniffing duration upon exposure to low concentrations of vitamin D while higher concentrations were less effective. It has been shown that vitamin D has pheromone-like properties in lizards. Our histochemical and behavioral observations indicate that the mammalian vomeronasal organ may be a vitamin D target. Olfactory functions of vitamin D involve most likely rapid membrane mediated effects rather than actions through nuclear receptors.

Approaches for the isolation and identification of hydrophilic, light-sensitive, volatile and minor natural products

Water-soluble, volatile, minor and photosensitive natural products are yet poorly known, and this review discusses the literature reporting the isolation strategies for some of these metabolites.

Medial Amygdala Kiss1 Neurons Mediate Female Pheromone Stimulation of Luteinizing Hormone in Male Mice

BACKGROUND/AIMS

The medial amygdala (MeA) responds to olfactory stimuli and alters reproductive physiology. However, the neuronal circuit that relays signals from the MeA to the reproductive axis remains poorly defined. This study aimed to test whether MeA kisspeptin (MeAKiss) neurons in male mice are sensitive to sexually relevant olfactory stimuli and transmit signals to alter reproductive physiology. We also investigated whether MeAKiss neurons have the capacity to elaborate glutamate and GABA neurotransmitters and potentially contribute to reproductive axis regulation.

METHODS

Using female urine as a pheromone stimulus, MeAKiss neuronal activity was analysed and serum luteinizing hormone (LH) was measured in male mice. Next, using a chemogenetic approach, MeAKiss neurons were bi-directionally modulated to measure the effect on serum LH and evaluate the activation of the preoptic area. Lastly, using in situ hybridization, we identified the proportion of MeAKiss neurons that express markers for GABAergic (Vgat) and glutamatergic (Vglut2) neurotransmission.

RESULTS

Male mice exposed to female urine showed a two-fold increase in the number of c-Fos-positive MeAKiss neurons concomitant with raised LH. Chemogenetic activation of MeAKiss neurons significantly increased LH in the absence of urine exposure, whereas inhibition of MeAKiss neurons did not alter LH. In situ hybridization revealed that MeAKiss neurons are a mixed neuronal population in which 71% express Vgat mRNA, 29% express Vglut2 mRNA, and 6% express both.

CONCLUSIONS

Our results uncover, for the first time, that MeAKiss neurons process sexually relevant olfactory signals to influence reproductive hormone levels in male mice, likely through a complex interplay of neuropeptide and neurotransmitter signalling.

Human Appeasing Pheromone (HAP) influence on behavior and psychopathological residual symptoms of patients with complex psychiatric disorders

This article is a case-report series showing the effectiveness of a three-month exposure to a synthetic analogue of Human Appeasing Pheromone as add-on strategy to psychopharmacological treatment on behavioral and residual symptoms of three patients suffering from severe psychiatric disorders with complex clinical pictures.

Effect of Copulins on Rating of Female Attractiveness, Mate-Guarding, and Self-Perceived Sexual Desirability

Olfaction and chemical signaling play an important role in the mating behaviors of many taxa, yet there is minimal empirical research on human putative pheromones. A mixture of five volatile fatty acids secreted vaginally, identified and named “copulins,” significantly increase in concentration during the follicular phase and decrease in concentration during the luteal phase in nonpill using women. Men exposed to copulins exhibit an increase in testosterone, are inhibited in discriminating the attractiveness of women’s faces, and behave less cooperatively. According to Anisogamy, Sexual Selection and Parental Investment Theory, mammalian males, having low cost and high benefit from any copulatory interaction, may adaptively utilize any useful cues to identifying ovulating females and adjust their behavior accordingly in order to maximize their potential reproductive success. In the current study, we attempted a replication of Jütte and Grammer’s finding indicating copulins inhibit the ability of men to discriminate attractiveness of women’s faces, and we examined the role of copulins in self-reported mate-guarding behaviors and self-perceived sexual desirability. We utilized a randomized placebo-controlled design and as predicted, results indicated men exposed to copulins were more likely to rate themselves as sexually desirable to women and, on average, the copulin group rated women’s faces as more attractive than controls. There were no significant findings with mate guarding.

Chemosensory Communication of Gender Information: Masculinity Bias in Body Odor Perception and Femininity Bias Introduced by Chemosignals During Social Perception

Human body odor is a source of important social information. In this study, we explore whether the sex of an individual can be established based on smelling axillary odor and whether exposure to male and female odors biases chemosensory and social perception. In a double-blind, pseudo-randomized application, 31 healthy normosmic heterosexual male and female raters were exposed to male and female chemosignals (odor samples of 27 heterosexual donors collected during a cardio workout) and a no odor sample. Recipients rated chemosensory samples on a masculinity-femininity scale and provided intensity, familiarity and pleasantness ratings. Additionally, the modulation of social perception (gender-neutral faces and personality attributes) and affective introspection (mood) by male and female chemosignals was assessed. Male and female axillary odors were rated as rather masculine, regardless of the sex of the donor. As opposed to the masculinity bias in the odor perception, a femininity bias modulating social perception appeared. A facilitated femininity detection in gender-neutral faces and personality attributes in male and female chemosignals appeared. No chemosensory effect on mood of the rater was observed. The results are discussed with regards to the use of male and female chemosignals in affective and social communication.

You Smell Dangerous: Communicating Fight Responses Through Human Chemosignals of Aggression

The ability to detect conspecifics that represent a potential harm for an individual represents a high survival benefit. Humans communicate socially relevant information using all sensory modalities, including the chemosensory systems. In study 1, we investigated whether the body odor of a stranger with the intention to harm serves as a chemosignal of aggression. Sixteen healthy male participants donated their body odor while engaging in a boxing session characterized by aggression-induction methods (chemosignal of aggression) and while performing an ergometer session (exercise chemosignal). Self-reports on aggression-related physical activity, motivation to harm and angry emotions selectively increased after aggression induction. In study 2, we examined whether receivers smelling such chemosignals experience emotional contagion (e.g., anger) or emotional reciprocity (e.g., anxiety). The aggression and exercise chemosignals were therefore presented to 22 healthy normosmic participants in a double-blind, randomized exposure during which affective/cognitive processing was examined (i.e., emotion recognition task, emotional stroop task). Behavioral results indicate that chemosignals of aggression induce an affective/cognitive modulation compatible with an anxiety reaction in the recipients. These findings are discussed in light of mechanisms of emotional reciprocity as a way to convey not only affective but also motivational information via chemosensory signals in humans.

D'scent of man: a comparative survey of primate chemosignaling in relation to sex

This article is part of a Special Issue (Chemosignals and Reproduction). As highly visual animals, primates, in general, and Old World species (including humans), in particular, are not immediately recognized for reliance in their daily interactions on olfactory communication. Nevertheless, views on primate olfactory acuity and the pervasiveness of their scent signaling are changing, with increased appreciation for the important role of body odors in primate social and sexual behavior. All major taxonomic groups, from lemurs to humans, are endowed with scent-producing organs, and either deposit or exude a wealth of volatile compounds, many of which are known semiochemicals. This review takes a comparative perspective to illustrate the reproductive context of primate signaling, the relevant information content of their signals, the sexually differentiated investigative responses generated, and the behavioral or physiological consequences of message transmission to both signaler and receiver. Throughout, humans are placed alongside their relatives to illustrate the evolutionary continuum in the sexual selection of primate chemosignals. This ever-growing body of evidence points to a critical role of scent in guiding the social behavior and reproductive function throughout the primate order.

Olfactory threshold for bourgeonal and sexual desire in young adult males

Olfactory receptors were found to be expressed also in human sperm giving rise to the hypothesis that they might play a role in fertility and sexual behavior. For instance, bourgeonal was demonstrated to be an agonist of sperm cells olfactory receptor, OR1D2. OR1D2 has been found to be expressed in human olfactory epithelium and to play a critical role in human sperm chemotaxis. Recent preliminary evidence showed that olfaction sensitivity (determined by n-butanol olfactory threshold) and sexual desire were associated in young adult males. It is reasonable to hypothesize that bourgeonal olfactory threshold could be related with human sexual behavior and desire. In 37 healthy young adult male volunteers (age range 20-36 years), the bourgeonal odor threshold and the intensity of sexual desire [the latter using the International Index of Erectile Function (IIEF) scale] were examined. In addition, samples of DNA were collected. Allele and genotype frequency of the OR1D2 single nucleotide polymorphisms (SNPs) were then evaluated in order to study the relationship between sexual desire and OR1D2 SNPs expression. The olfactory threshold was categorized as <10, 10⩽threshold<15, 15⩽threshold<20, ⩾20. IIEF 1 and IIEF 2 scores were significantly associated. IIEF1 scores, but not IIEF2 scores were significantly associated with olfactory threshold. No statistically significant associations were found neither between genotypes frequency and sexual desire (IIEF1 and IIEF2), nor between genotypes frequency and olfactory threshold. Hypothesizing for the first time the relationship between bourgeonal olfactory sensitivity and sexual desire in a group of young adult males, the present study found a significant association between lower olfactory threshold for bourgeonal and stronger sexual desire, in terms of IIEF1.

New insights on food intake control by olfactory processes: the emerging role of the endocannabinoid system

The internal state of the organism is an important modulator of perception and behavior. The link between hunger, olfaction and feeding behavior is one of the clearest examples of these connections. At the neurobiological level, olfactory circuits are the targets of several signals (i.e. hormones and nutrients) involved in energy balance. This indicates that olfactory areas are potential sensors of the internal state of the organism. Thus, the aim of this manuscript is to review the literature showing the interplay between metabolic signals in olfactory circuits and its impact on food intake.

Sexual selection and the evolution of behavior, morphology, neuroanatomy and genes in humans and other primates

Explaining human evolution means developing hypotheses about the occurrence of sex differences in the brain. Neuroanatomy is significantly influenced by sexual selection, involving the cognitive domain through competition for mates and mate choice. Male neuroanatomy emphasizes subcortical brain areas and visual-spatial skills whereas that of females emphasizes the neocortex and social cognitive areas. In primate species with high degrees of male competition, areas of the brain dealing with aggression are emphasized. Females have higher mirror neuron activity scores than males. Hundreds of genes differ in expression profiles between males and females. Sexually selected differences in gene expression can produce neuroanatomical sex differences. A feedback system links genes, gene expression, hormones, morphology, social structure and behavior. Sex differences, often through female choice, can be rapidly modulated by socialization. Human evolution is a dramatic case of how a trend toward pair bonding and monogamy lowered male competition and increased female choice as a necessary step in releasing the cognitive potential of our species.

Feminized behavior and brain gene expression in a novel mouse model of Klinefelter Syndrome

Klinefelter Syndrome (KS) is the most common sex chromosome aneuploidy in men and is characterized by the presence of an additional X chromosome (XXY). In some Klinefelter males, certain traits may be feminized or shifted from the male-typical pattern towards a more female-typical one. Among them might be partner choice, one of the most sexually dimorphic traits in the animal kingdom. We investigated the extent of feminization in XXY male mice (XXYM) in partner preference and gene expression in the bed nucleus of the stria terminalis/preoptic area and the striatum in mice from the Sex Chromosome Trisomy model. We tested for partner preference using a three-chambered apparatus in which the test mouse was free to choose between stimulus animals of either sex. We found that partner preference in XXYM was feminized. These differences were likely due to interactions of the additional X chromosome with the Y. We also discovered genes that differed in expression in XXYM versus XYM. Some of these genes are feminized in their expression pattern. Lastly, we also identified genes that differed only between XXYM versus XYM and not XXM versus XYM. Genes that are both feminized and unique to XXYM versus XYM represent strong candidates for dissecting the molecular pathways responsible for phenotypes present in KS/XXYM but not XXM. In sum, our results demonstrated that investigating behavioral and molecular feminization in XXY males can provide crucial information about the pathophysiology of KS and may aid our understanding of sex differences in brain and behavior.

Wild western lowland gorillas signal selectively using odor

Mammals communicate socially through visual, auditory and chemical signals. The chemical sense is the oldest sense and is shared by all organisms including bacteria. Despite mounting evidence for social chemo-signaling in humans, the extent to which it modulates behavior is debated and can benefit from comparative models of closely related hominoids. The use of odor cues in wild ape social communication has been only rarely explored. Apart from one study on wild chimpanzee sniffing, our understanding is limited to anecdotes. We present the first study of wild gorilla chemo-communication and the first analysis of olfactory signaling in relation to arousal levels and odor strength in wild apes. If gorilla scent is used as a signaling mechanism instead of only a sign of arousal or stress, odor emission should be context specific and capable of variation as a function of the relationships between the emitter and perceiver(s). Measured through a human pungency scale, we determined the factors that predicted extreme levels of silverback odor for one wild western lowland gorilla (Gorilla gorilla gorilla) group silverback. Extreme silverback odor was predicted by the presence and intensity of inter-unit interactions, silverback anger, distress and long-calling auditory rates, and the absence of close proximity between the silverback and mother of the youngest infant. Odor strength also varied according to the focal silverback's strategic responses during high intensity inter-unit interactions. Silverbacks appear to use odor as a modifiable form of communication; where odor acts as a highly flexible, context dependent signaling mechanism to group members and extra-group units. The importance of olfaction to ape social communication may be especially pertinent in Central African forests where limited visibility may necessitate increased reliance on other senses.

Chemical mating cues in C. elegans

In the natural environment it is vital that organisms are capable of locating mates to reproduce and, consequently, increase the diversity of their gene pool. Many species make use of audio and visual communication for mate location. However, the more ancient form of chemical communication is used by all forms of life, from bacteria to mammals. In the past decade, much information has been discovered regarding pheromones in the nematode Caenorhabditis elegans. In this review, chemical signals that govern mating behavior in C. elegans will be discussed, from the existence and identification of mating cues, to the neurons involved in the behavioral response. Specifically, mate attraction is dictated by specific glycosides and side chains of the dideoxysugar ascarylose, a class of molecules known as ascarosides. Intriguingly, modifications of the ascarosides can dictate different behaviors such as male attraction, hermaphrodite attraction, and dauer formation. In general, interactions between core sensory neurons such as ASK and sex-specific neurons like CEM are critical for detecting these small molecules. These data reveal the existence of a complex, synergistic, chemical mating cue system between males and hermaphrodites in C. elegans, thereby highlighting the importance of mate attraction in a primarily hermaphroditic population.

Evaluating the binding efficiency of pheromone binding protein with its natural ligand using molecular docking and fluorescence analysis

Chemosignals play a crucial role in social and sexual communication among inter- and intra-species. Chemical cues are bound with protein that is present in the pheromones irrespective of sex are commonly called as pheromone binding protein (PBP). In rats, the pheromone compounds are bound with low molecular lipocalin protein α2u-globulin (α2u). We reported farnesol is a natural endogenous ligand (compound) present in rat preputial gland as a bound volatile compound. In the present study, an attempt has been made through computational method to evaluating the binding efficiency of α2u with the natural ligand (farnesol) and standard fluorescent molecule (2-naphthol). The docking analysis revealed that the binding energy of farnesol and 2-naphthol was almost equal and likely to share some binding pocket of protein. Further, to extrapolate the results generated through computational approach, the α2u protein was purified and subjected to fluorescence titration and binding assay. The results showed that the farnesol is replaced by 2-naphthol with high hydrophobicity of TYR120 in binding sites of α2u providing an acceptable dissociation constant indicating the binding efficiency of α2u. The obtained results are in corroboration with the data made through computational approach.

Human Body Scents: Do they Influence our Behavior?

Pheromonal communication in the animal world has been of great research interest for a long time. While extraordinary discoveries in this field have been made, the importance of the human sense of smell was of far lower interest. Humans are seen as poor smellers and therefore research about human olfaction remains quite sparse compared with other animals. Nevertheless amazing achievements have been made during the past 15 years. This is a collection of available data on this topic and a controversial discussion on the role of putative human pheromones in our modern way of living. While the focus was definitely put on behavioral changes evoked by putative human pheromones this article also includes other important aspects such as the possible existence of a human vomeronasal organ. If pheromones do have an influence on human behavior there has to be a receptor organ. How are human body scents secreted and turned into odorous substances? And how can con-specifics detect those very odors and transmit them to the brain? Apart from that the most likely candidates for human pheromones are taken on account and their impact on human behavior is shown in various detail.

Examining the possible functions of kissing in romantic relationships

Recent research suggests that romantic kissing may be utilized in human sexual relationships to evaluate aspects of a potential mate's suitability, to mediate feelings of attachment between pair-bonded individuals, or to facilitate arousal and initiate sexual relations. This study explored these potential functions of romantic kissing by examining attitudes towards the importance of kissing in the context of various human mating situations. The study involved an international online questionnaire, which was completed by 308 male and 594 female participants aged 18-63 years. Support was found for the hypothesis that kissing serves a useful mate-assessment function: women, high mate-value participants, and participants high in sociosexual orientation placed greater importance on kissing in romantic relationships and stated that an initial kiss was more likely to affect their attraction to a potential mate than did men, low-mate value participants or low sociosexual orientation participants. Kissing also seemed to be utilized in the mediation of pair-bond attachments: kissing was seen to be more important at established stages of relationships by low sociosexual participants, kissing was generally seen as more important in long-term relationship contexts (but particularly so by women), and kissing frequency was found to be related to relationship satisfaction. The findings of this research showed very little evidence to support the hypothesis that the primary function of kissing is to elevate levels of arousal.

Do men's faces really signal heritable immunocompetence?

In the literature on human mate choice, masculine facial morphology is often proposed to be an intersexual signal of heritable immunocompetence, and hence an important component of men's attractiveness. This hypothesis has received considerable research attention, and is increasingly treated as plausible and well supported. In this article, we propose that the strength of the evidence for the immunocompetence hypothesis is somewhat overstated, and that a number of difficulties have been under-acknowledged. Such difficulties include (1) the tentative nature of the evidence regarding masculinity and disease in humans, (2) the complex and uncertain picture emerging from the animal literature on sexual ornaments and immunity, (3) the absence of consistent, cross-cultural support for the predictions of the immunocompetence hypothesis regarding preferences for masculinized stimuli, and (4) evidence that facial masculinity contributes very little, if anything, to overall attractiveness in real men. Furthermore, alternative explanations for patterns of preferences, in particular the proposal that masculinity is primarily an intrasexual signal, have been neglected. We suggest that immunocompetence perspectives on masculinity, whilst appealing in many ways, should still be regarded as speculative, and that other perspectives-and other traits-should be the subject of greater attention for researchers studying human mate preferences.

Olfactory Sensitivity and Sexual Desire in Young Adult and Elderly Men: An Introductory Investigation

Background

It has been suggested that olfaction could influence human sexual behavior. Age is negatively associated with many aspects of sexuality and, with increasing age, people tend to show a declining sexual desire. The present pilot study investigated the relationship between sexual desire and olfactory sensitivity in healthy men of two age groups, young adult and elderly (≥65 years old), to ascertain whether their sense of smell could determine sexual desire and whether an age-related weaker olfactory sensitivity could correlate with the decline in sexual appetite in elderly patients.

Methods

Sixty-three volunteers were recruited and divided into two groups, one consisting of 48 healthy young adult men, the other of 15 healthy elderly men. All participants were tested to ascertain their odor threshold for n-butanol (Sniffin’ Sticks) and their sexual desire using the International Index of Erectile Function (IIEF), presenting only the questions relating to frequency (IIEF1) and level (IIEF2) of sexual desire.

Results

Sexual desire and mean olfactory thresholds were higher in the younger adults than in the elderly men (p = 0.001 and p = 0.02, respectively). There was a significant association between butanol threshold and sexual desire for the young adult group (p = 0.02), but not for the elderly group (p = 0.35).

Conclusion

This study found a preliminary association between olfaction and sexual behavior, in young adults at least. More studies are needed to improve our knowledge in this intriguing field, possibly using electrophysiological olfactory methods.

Personality psychology: lexical approaches, assessment methods, and trait concepts reveal only half of the story--why it is time for a paradigm shift

This article develops a comprehensive philosophy-of-science for personality psychology that goes far beyond the scope of the lexical approaches, assessment methods, and trait concepts that currently prevail. One of the field's most important guiding scientific assumptions, the lexical hypothesis, is analysed from meta-theoretical viewpoints to reveal that it explicitly describes two sets of phenomena that must be clearly differentiated: 1) lexical repertoires and the representations that they encode and 2) the kinds of phenomena that are represented. Thus far, personality psychologists largely explored only the former, but have seriously neglected studying the latter. Meta-theoretical analyses of these different kinds of phenomena and their distinct natures, commonalities, differences, and interrelations reveal that personality psychology's focus on lexical approaches, assessment methods, and trait concepts entails a) erroneous meta-theoretical assumptions about what the phenomena being studied actually are, and thus how they can be analysed and interpreted, b) that contemporary personality psychology is largely based on everyday psychological knowledge, and c) a fundamental circularity in the scientific explanations used in trait psychology. These findings seriously challenge the widespread assumptions about the causal and universal status of the phenomena described by prominent personality models. The current state of knowledge about the lexical hypothesis is reviewed, and implications for personality psychology are discussed. Ten desiderata for future research are outlined to overcome the current paradigmatic fixations that are substantially hampering intellectual innovation and progress in the field.

Subliminally perceived odours modulate female intrasexual competition: an eye movement study

BACKGROUND

Evidence suggests that subliminal odorants influence human perception and behavior. It has been hypothesized that the human sex-steroid derived compound 4,16-androstadien-3-one (androstadienone) functions as a human chemosignal. The most intensively studied steroid compound, androstadienone is known to be biologically relevant since it seems to convey information about male mate quality to women. It is unclear if the effects of androstadienone are menstrual cycle related.

METHODOLOGY/PRINCIPAL FINDINGS

In the first experiment, heterosexual women were exposed to androstadienone or a control compound and asked to view stimuli such as female faces, male faces and familiar objects while their eye movements were recorded. In the second experiment the same women were asked to rate the level of stimuli attractiveness following exposure to the study or control compound. The results indicated that women at high conception risk spent more time viewing the female than the male faces regardless of the compound administered. Women at a low conception risk exhibited a preference for female faces only following exposure to androstadienone.

CONCLUSIONS/SIGNIFICANCE

We contend that a woman's level of fertility influences her evaluation of potential competitors (e.g., faces of other women) during times critical for reproduction. Subliminally perceived odorants, such as androstadienone, might similarly enhance intrasexual competition strategies in women during fertility phases not critical for conception. These findings offer a substantial contribution to the current debate about the effects that subliminally perceived body odors might have on behavior.

Chemical communication and mother-infant recognition

Fifty years after the term "pheromone" was coined by Peter Karlson and Martin Lüsher the search for these semiochemicals is still an elusive goal of chemical ecology and communication studies. Contrary to what appears in the popular press, the race is still on to capture and define human scents. Over the last several years, it became increasingly clear that pheromone-like chemical signals probably play a role in offspring identification and mother recognition. Recently, we analyzed the volatile compounds in sweat patch samples collected from the para-axillary and nipple-areola regions of women during pregnancy and after childbirth. We hypothesized that, at the time of birth and during the first weeks of life, the distinctive olfactory pattern of the para-axillary area is probably useful to newborns for recognizing and distinguishing their own mother, whereas the characteristic pattern of the nipple-areola region is probably useful as a guide to nourishment.

In the nose of the beholder: are olfactory influences on human mate choice driven by variation in immune system genes or sex hormone levels?

The human leukocyte antigen (HLA) is the most polymorphic region of the genome, coding for proteins that mediate human immune response. This polymorphism may be maintained by balancing selection and certain populations show deviations from expected gene frequencies. Supporting this hypothesis, studies into olfactory preferences have suggested that females prefer the scent of males with dissimilar HLA to their own. However, it has also been proposed that androstenones play a role in female mate choice, and as these molecules inhibit the immune system, this has implications for the theory of HLA-driven mate preference. This review will critically analyze the findings of studies investigating olfactory preference in humans, and their implications for these two contrasting theories of mate choice.

Male axillary extracts modify the affinity of the platelet serotonin transporter and impulsiveness in women

The presence of functional pheromones in axillary extracts in humans is still matter of debate. Scattered data suggest that unidentified human axillary compounds with pheromonal activity may influence mood and this may occur, perhaps, through the modulation of the serotonin (5-HT) system that has been linked to mood by several findings. Therefore, the aim of this study was to assess the possible changes of a peripheral marker of the 5-HT system, i.e., the platelet 5HT transporter, and of some psychological tests, in a group of women who were exposed to male axillary extracts (group 1). A matched group of women who underwent an exposure to a neutral solution, were used as control subjects (group 2). The 5-HT transporter was evaluated by means of the specific binding of (3)H-paroxetine ((3)H-Par) to platelet membranes, as well as by means of (3)H-5-HT reuptake in whole platelets, at baseline (T0) and 1h after the stimulation (T1). The following tests were used: the "Experiences in Close Relationships" questionnaire (ECR), the latest version of the Barratt Impulsiveness Scale (BIS-11) and the Structured Clinical Interview for Mood Spectrum, self-reported version. The dissociation constant (Kd) of (3)H-Par binding showed a significant decrease at T1 only in the women exposed to male axillary extracts, as compared with baseline values, while the Bmax and (3)H-5-HT reuptake parameters did not show any change in both groups. The correlation analyses showed that at T0, the Kd values correlated significantly and positively with the factor of motor impulsiveness in all subjects. Two factors of the BIS-11, in particular, the attentional and the motor impulsiveness were significantly lower at T1 in the group 1. Further, at T1 and still in the group 1, a significant and positive correlation was measured between the Kd values and two ECR attachment styles, the secure and preoccupied, as well as with the ECR anxiety scale. Taken together, these findings suggest that the application of male axillary extracts to women may modify the affinity of their platelet 5-HT transporter, as well as of some impulsiveness and romantic attachment characteristics. The substances responsible for this effect remain to be identified.

Apocrine sweat gland obstruction by antiperspirants allowing transdermal absorption of cutaneous generated hormones and pheromones as a link to the observed incidence rates of breast and prostate cancer in the 20th century

Breast and prostate cancer share similarities and likely represent homologous cancers in females and males, respectively. The role of hormones such as testosterone and estrogen in carcinogenesis is well established. Despite worldwide research efforts, the pathogenesis of these diseases is largely not well understood. Personal care products containing estrogens or xenoestrogens have raised concern as a breast cancer risk, especially in young African-American women. In the United States (US) there is a parallel rise in the incidence in breast and prostate cancer compared to selected non-hormone dependent tumors. Observed US and global breast and prostate cancer incidence increases were occurring before exogenous hormone replacement and xenoestrogen exposure were commonplace. An unintentional, inadvertent, and long term hormone exposure may occur from transdermal absorption of sex hormones and pheromones (androgens) from axillary apocrine sweat gland obstruction by aluminum-based antiperspirants. The global rise in antiperspirant use parallels rises in breast and prostate cancer incidence and mortality rates. A multi-disciplinary literature based set of evidence is presented on how such a link is possible, to prompt confirmatory investigations in the pursuit of unmet needs in breast and prostate cancer etiology and prevention.

A dual physiological character for sexual function: libido and sexual pheromones

Human sexual response is a complex function involving many cerebral, spinal and peripheral aspects; the last are relatively known and benefit from good pharmacological control, as in the case of erectile dysfunction. Spinal cord sexual reflexes also have a good theoretical and experimental description. There is minimal understanding of the cerebral sexual processes (libido, sexual arousal, orgasm). The initial perspective was that the cerebral areas implied in sexuality exert descending stimulatory and inhibitory influences on spinal cord sexual centres/reflexes. This was a wrong supposition, which inhibited progress in this subject, with a considerable impact on a subject's individual and social life. A new approach to sexual function arises from the idea that simple neurological structures can support only simple functions, while a more complex function requires correspondingly complex anatomical structures. For this reason the spinal cord would not be able to realise the integration of multiple (spinal and psychosensorial) stimuli into a unique and coherent ejaculation response. Consequently, all mechanisms implied in human sexuality would be cerebral processes, ejaculation reflexes ascending in evolution to the cerebral level. This new evolutionary concept was developed after 2001 in five distinct articles on the cerebral duality of sexual arousal, sexual hormones, ejaculation and serotonergic receptors. During this period other published results suggested a possible cerebral duality for sexual pheromones and libido in humans. All these dual physiological aspects are integrated in this review into one neurophysiological model, thus trying to further develop the new concepts of sexual function and perhaps relational behaviour. In conclusion, ejaculation is a dual cerebral process with arousal sensation (hormonally modulated) and libido perception (pheromonally modulated) as the afferent part. Two neurophysiological axes could exist in both men and women. In this assumption the mechanisms for libido and sexual arousal are not the only ones invoked, their correlations and implications are also suggested, perhaps critical aspects for further developments in the field.