Menstrual synchrony was first demonstrated in a 1971 paper published in Nature by Martha McClintock. […]

she asked 135 college girls living in dorms to recall their period start dates at three times throughout the academic year. She found that close-friend groups had periods significantly closer together in April (later in the year) compared with October: lessening from an average of 6.4 to 4.6 days apart.

The phenomenon was dubbed “the McClintock effect” and is widely held as the first example of pheromones — unconscious chemical signals that influence behavior and physiology — among humans. […] Many subsequent researchers went on to reproduce the results from McClintock’s original experiment in people, rats, hamsters and chimpanzees.

But a cohort of studies that found no evidence for menstrual synchrony began to grow, too. […]

In 1992 H. Clyde Wilson […] re-analyzed McClintock’s first experiment, along with a few others that used a similar design. He found that all had inflated the difference between period start dates at the beginning of their studies […] their model of two pheromones — one that pulls ovulation forward and one that delays it — driving synchrony didn’t work […]

The insurmountable hurdle in all the studies is that women often have persistent cycles of different lengths. As such, they can never truly synchronize, just randomly phase in and out of synchrony over the months as their cycles diverge and converge. […]

But a team of Japanese researchers at Yokohama City University, led by Kazuyuki Shinohara, also found in a series of papers that donor women undergoing these two phases of the menstrual cycle release compounds that when inhaled by other women can significantly impact the frequency in the latter of pulses of luteinizing hormone (LH), which helps control the timing of ovulation and cycle length.

{ Scientific American | Continue reading }

Again and again in the animal world, males have shorter lifespans than females, an effect scientists attribute in part to the deleterious effects of testosterone.

[In 2012,] researchers who looked at historical records of Korean eunuchs castrated during boyhood found that the eunuchs lived considerably longer than ordinary, testicled men. […]

testosterone, a hormone involved in testes growth, muscle development and aggression, but that also seems to have an immune system-weakening effect. […] Women do tend to live longer than men, but that could be for other reasons, including the longevity-enhancing effects of estrogen, the female sex hormone.

{ Wired | Continue reading }

photo { Robert Mapplethorpe, Tattoo Artist’s Son (1984) }

Romantic love is a basic brain system, like fear and anger or disgust. We humans have evolved three distinct brain systems for mating and reproduction: the sex drive, romantic love, and feelings of deep attachment. People make the mistake of thinking that these are phases. They’re not phases, they’re brain systems, and they can operate in any combination and order. […]

I estimate the people I studied, on average, thought about their beloved about 85 percent of the time. […]

I looked at the demographics from the United Nations from 1947–2011 and across 80 cultures. People tend to divorce around the fourth year of marriage. […]

{ Helen Fisher / Sapiens | Continue reading }

still { Catherine Deneuve in Jacques Demy’s Les Parapluies de Cherbourg, 1963 }

Two studies done at the University of Minnesota Medical School and published in the early 1980’s measured the intensity, frequency, and durations of pelvic muscle contractions (measured with a pressure sensitive anal probe) of males and females during masturbation. There was basically no difference in the pattern of these contractions between males and females. […] A study done at Stanford University in 1994 found no significant gender differences in observed increases in heart rate, blood pressure, oxytocin, and anal contractions during orgasm.

{ Psychology Today | Continue reading }

The refractory period is the recovery phase after orgasm during which it is physiologically impossible for a man to have additional orgasms. This phase begins immediately after ejaculation. […] Although it is generally reported that women do not experience a refractory period and can thus experience an additional orgasm (or multiple orgasms) soon after the first one, some sources state that […] women may also experience a moment after orgasm in which further sexual stimulation does not produce excitement. […] clitoral hypersensitivity after orgasm can effectively create a refractory period. these women may be capable of further orgasms, but the pain involved in getting there makes the prospect undesirable. […]

the refractory period varies widely among individuals, ranging from minutes to days […] According to some studies, 18-year-old males have a refractory period of about 15 minutes, while those in their 70s take about 20 hours, with the average for all men being about half an hour. Although rarer, some males exhibit no refractory period or a refractory period lasting less than 10 seconds. […]

An increased infusion of the hormone oxytocin during ejaculation is believed to be chiefly responsible for the male refractory period, and the amount by which oxytocin is increased may affect the length of each refractory period. Another chemical which is considered to be responsible for the male refractory period is prolactin, which is repressed by dopamine, and is responsible for sexual arousal. […]

One alternative theory explains the male refractory period in terms of a peripheral autonomic feedback mechanism, rather than through central chemicals like oxytocin, serotonin, and prolactin. Autonomic feedback is already known to regulate other physiologic systems, such as breathing, blood pressure, and gut motility. This theory suggests that after male ejaculation, decreased wall tension in structures such as the seminal vesicles leads to a change in the fine autonomic signals sent from these organs, effectively creating a negative feedback loop. Such a mechanism is similar to decreased gastric and bowel motility once gastric contents have passed through. Once the feedback loop has been created, the refractory period remains until the loop is broken through restoration of the wall tension in the seminal vesicles. As men age, the time to restore tension in the seminal vesicles increases.

{ Wikipedia | Continue reading }

During my clinical internship over 20 years ago, my boss, a psychiatrist, asked me to research how PMS prevents women from thinking clearly. I told him he was a relic of the Stone Age. Women were as consistently clearheaded as men, if not more so.

But recently, a researcher in my lab, Joe Andreano, an expert on female hormones, showed me some surprising data. As a woman’s levels of progesterone and estrogen vary, so does the connectivity between two brain networks: the default mode network and the salience network. These networks play key roles in creating your emotional life.

If I hadn’t seen the data with my own eyes, I wouldn’t have believed it.

When scientists say that brain networks are “strongly connected” or have “increased connectivity,” it means that the neurons have an easier time passing information back and forth. In the case of the default mode and salience networks, increased connectivity means (among other things) that you may experience more powerful negative emotions. In earlier research, for example, my colleagues and I found that people reported more intense sadness when watching the sentimental movie “Stepmom” and more intense fear when watching the horror movie “The Ring Two” in the moments when these brain networks were more connected.

There has also been a flurry of recent studies indicating that certain cocktails of ovarian hormones can make women feel lousy, particularly a week or so before menstruation. Female test subjects who receive ovarian hormones designed to mimic the menstrual cycle, for example, report an increase in negative mood. They also remember negative material better, and they show enhanced stress responses. […]

 I’m not saying that women turn into helpless snowflakes for a few days each month. I’m just saying that the biology is real: Some women may have a short window before their period when, if something bad happens, they will feel more negative or stressed and will remember that unpleasant event more easily.

A few bad feelings or memories aren’t inherently harmful, of course. But this window of vulnerability, combined with other risk factors, could increase the odds of developing mood disorders like depression.

{ NY Times | Continue reading }

enamel on linen { Christopher Wool, Untitled, 1998 }

Why the Victorian era saw a surge in female births and war begets boys

There is empirical evidence that heavy sexual activity increases the chances that conception will occur before the most fertile time of the female cycle, as the woman may be pregnant by then. And the data also suggest that, possibly for hormonal reasons, such conceptions are slightly more likely to be boys. “It doesn’t take much imagination to suppose that the ends of wars, with servicemen home on leave or returning home, are associated with fairly intense sex – more babies were born in the UK in 1919 than any other year in history. Put all these together and you get the conclusion – frantic fornication breeds boys.”

[…]

Which brings us back to the mysterious surge of female births in the late Victorian period. Could it be that, in the same vein in which heavy sexual activity increases the sex ratio, a  trend towards sexual inactivity lowers it? “Victorian morality” distinguished itself through a set of values that espoused sexual restraint, with an increased condemnation of masturbation and sexual activity in general, repressing any form of sexuality other than penetrative intercourse. And indeed, statistics reflect a steady decline of sexual activity throughout the Victorian period, reaching its lowest point in the year 1898. But as there was less sex going on, conception tended to occur around the most fertile time of the months, bestowing a (relative) excess of baby girls on the Victorians.

{ Rolf Degen | Continue reading }

Hypothesis 1

Up to circa two decades age, it was generally supposed – but without hard supporting evidence – that pregnant women exposed to adverse environmental circumstances were at increased risk of foetal loss, and that male foetuses were at greater risk than female foetuses; and that therefore the liveborn infants produced by stressed women contained a higher proportion of daughters. That hard evidence has now been accumulated in a series of papers by Catalano and colleagues, and others.

Using time-series analysis, it has been shown that the Sex ratios at birth (SRB) briefly declined, slightly but significantly, some three to five months after many catastrophic and other adverse events e.g. the terrorist attacks on September 11th, 2001; the Troubles in Northern Ireland (1969–1998), the Breivik shooting in 2011 in Norway, the Sandy Hook shooting in 2012 in Connecticut; the assassination of President Kennedy [though the effect in this case was more marked in non-White than White births]. […]

Thus there is overwhelming evidence that sex ratios at birth are partially controlled by maternal stress-induced selective culling of frail males in utero, resulting in a conception cohort with a low sex ratio at birth. It has also been postulated that the ratio may be skewed because of fertilization of non-optimally matured oocytes under these circumstances. Moreover, it has also been hypothesized that higher coital rates will lead to ejaculation of newly formed spermatozoa cells, possibly leading to a preponderance of Y-sperm since it is also hypothesized that X-sperm age faster and are eliminated earlier.

However, it will be appreciated that selective culling of frail males during pregnancy cannot explain some of the established variations of SRB. First, it cannot explain why some reported sex ratios are higher than prevailing norms. Second, it cannot explain why these norms almost always exceed 0.5 (equal numbers of males and females).

Hypothesis 2

It has been hypothesized that human sex ratios at birth are partially controlled by the parental hormone levels of both parents around the time of conception. Ex hypothesi, high levels of testosterone (in either parent) and/or of oestrogen (in the mother), are associated with subsequent male births. And high levels of gonadotrophins (in either parent) are associated with subsequent female births. Most of this evidence is observational and correlational, and is in accordance with the hypothesis of Trivers & Willard.

{ Early Human Development | Continue reading }

lithograph { Ellsworth Kelly, Small Blue Curve, 2013 }

Because ovulating (i.e., high-fertility) women are both more attractive to men and also more attracted to (desirable) men, ovulating women may be perceived to pose heightened threats to other women’s romantic relationships. Across 4 experiments, partnered women were exposed to photographs of other women taken during either their ovulatory or nonovulatory menstrual-cycle phases, and consistently reported intentions to socially avoid ovulating (but not nonovulating) women - but only when their own partners were highly desirable. Exposure to ovulating women also increased women’s sexual desires for their (highly desirable) partners. These findings suggest that women can be sensitive to subtle cues of other women’s fertility and respond (e.g., via social exclusion, enhanced sexual attention to own mate) in ways that may facilitate their mate retention goals while not thwarting their affiliative goals.

{ Journal of Personality and Social Psychology | Continue reading }

Using luteinizing hormone tests to verify ovulation, across two studies (Samples 1 and 2), we found that women whose partners were relatively low in sexual desirability felt less close to their partner (Samples 1 and 2) and were more critical of their partner’s faults (Sample 2) on high-fertility days of the cycle just prior to ovulation compared with low-fertility days of the cycle. Women whose partners were relatively high in sexual desirability felt closer to their partner (Sample 1) and more satisfied with their relationship (Sample 2) on high- than low-fertility days of the cycle. There were no such shifts in women’s commitment to their relationship. Therefore, partner sexual desirability predicts women’s high-fertility assessments of relationship quality but not their intentions to stay in their relationship, consistent with the dual mating hypothesis. These findings suggest that variations across the ovulation cycle in women’s reproductive hormones play an important role in relationship dynamics.

{ Hormones and Behavior | PDF }

images { 1. Frederike Helwig | 2. Bonnie and Clyde (1967), publicity still, Faye Dunaway }

Research has found that estradiol positively and progesterone negatively predicts women’s sexual desire. […]

The current study extended these findings by examining, within a sample of 33 naturally cycling women involved in romantic relationships, hormonal correlates of sexual attraction to or interests in specific targets: women’s own primary partner [in-pair] or men other than women’s primary partner [extra-pair]. […]

Whereas estradiol levels were associated with relatively greater extra-pair sexual interests than in-pair sexual interests, progesterone levels were associated with relatively greater in-pair sexual interests.

{ Hormones and Behavior | Continue reading }

photo { Maxime Ballesteros }

Research has shown that humans consciously use alcohol to encourage sexual activity. […]

In the current study, we examined if males exposed without their knowledge to pheromones emitted by fertile females would increase their alcohol consumption, presumably via neurobehavioral information pathways that link alcohol to sex and mating. We found that men who smelled a T-shirt worn by a fertile female drank significantly more (nonalcoholic) beer, and exhibited significantly greater approach behavior toward female cues, than those who smelled a T-shirt worn by a nonfertile female.

{ Experimental and Clinical Psychopharmacology | Continue reading }

photo { Miss August, 1957 }

Recent studies have shown that women are more sensitive than men to subtle cuteness differences in infant faces. It has been suggested that raised levels in estradiol and progesterone may be responsible for this advantage. […]

Thirty-six women were tested once during ovulation and once during the luteal phase of their menstrual cycle. In a two alternative forced-choice experiment, participants chose the baby which they thought was cuter (Task 1), younger (Task 2), or the baby that they would prefer to babysit (Task 3). […]

During ovulation, women were more likely to choose the cuter baby than during the luteal phase, in all three tasks. These results suggest that cuteness discrimination may be driven by cyclic hormonal shifts.

{ Hormones and Behavior | Continue reading }

art { Henri Chopin, La crevette amoureuse, 1967-1975 }

The idea of two sexes is simplistic. Biologists now think there is a wider spectrum than that.

The presence or absence of a Y chromosome is what counts: with it, you are male, and without it, you are female. But doctors have long known that some people straddle the boundary — their sex chromosomes say one thing, but their gonads (ovaries or testes) or sexual anatomy say another. Parents of children with these kinds of conditions — known as intersex conditions, or differences or disorders of sex development (DSDs) — often face difficult decisions about whether to bring up their child as a boy or a girl. Some researchers now say that as many as 1 person in 100 has some form of DSD. […]

That the two sexes are physically different is obvious, but at the start of life, it is not. Five weeks into development, a human embryo has the potential to form both male and female anatomy. Next to the developing kidneys, two bulges known as the gonadal ridges emerge alongside two pairs of ducts, one of which can form the uterus and Fallopian tubes, and the other the male internal genital plumbing: the epididymes, vas deferentia and seminal vesicles. At six weeks, the gonad switches on the developmental pathway to become an ovary or a testis. If a testis develops, it secretes testosterone, which supports the development of the male ducts. It also makes other hormones that force the presumptive uterus and Fallopian tubes to shrink away. If the gonad becomes an ovary, it makes oestrogen, and the lack of testosterone causes the male plumbing to wither. The sex hormones also dictate the development of the external genitalia, and they come into play once more at puberty, triggering the development of secondary sexual characteristics such as breasts or facial hair. […]

For many years, scientists believed that female development was the default programme, and that male development was actively switched on by the presence of a particular gene on the Y chromosome. In 1990, researchers made headlines when they uncovered the identity of this gene, which they called SRY. Just by itself, this gene can switch the gonad from ovarian to testicular development. For example, XX individuals who carry a fragment of the Y chromosome that contains SRY develop as males.

{ Nature | Continue reading }

Does morality depend on the time of the day? The study “The Morning Morality Effect: The Influence of Time of Day on Unethical Behavior” published in October of 2013 by Maryam Kouchaki and Isaac Smith suggested that people are more honest in the mornings, and that their ability to resist the temptation of lying and cheating wears off as the day progresses. […]

One question not addressed by Kouchaki and Smith was whether the propensity to become dishonest in the afternoons or evenings could be generalized to all subjects or whether the internal time in the subjects was also a factor.

All humans have an internal body clock — the circadian clock — which runs with a period of approximately 24 hours. The circadian clock controls a wide variety of physical and mental functions such as our body temperature, the release of hormones or our levels of alertness. The internal clock can vary between individuals, but external cues such as sunlight or the social constraints of our society force our internal clocks to be synchronized to a pre-defined external time which may be quite distinct from what our internal clock would choose if it were to “run free”. Free-running internal clocks of individuals can differ in terms of their period (for example 23.5 hours versus 24.4 hours) as well as the phases of when individuals would preferably engage in certain behaviors. […]

Some people like to go to bed early, wake up at 5 am or 6 am on their own even without an alarm clock and they experience peak levels of alertness and energy before noon. In contrast to such “larks”, there are “owls” among us who prefer to go to bed late at night, wake up at 11 am, experience their peak energy levels and alertness in the evening hours and like to stay up way past midnight. […]

The researchers Brian Gunia, Christopher Barnes and Sunita Sah therefore decided to replicate the Kouchaki and Smith study with one major modification: They not only assessed the propensity to cheat at different times of the day, they also measured the chronotypes of the study participants. Their recent paper “”The Morality of Larks and Owls: Unethical Behavior Depends on Chronotype as Well as Time of Day” confirms that Kouchaki and Smith findings that the time of the day influences honesty, but the observed effects differ among chronotypes. […]

[M]orning morality effect and the idea of “moral exhaustion” towards the end of the day cannot be generalized to all. In fact, evening people (”owls”) are more honest in the evenings. […]

Gunia and colleagues only included morning and evening people in their analysis and excluded the participants who reported an intermediate chronotype, i.e. not quite early morning “larks” and not true “owls”. This is a valid criticism because newer research on chronotypes has shown that there is a Gaussian distribution of chronotypes. Few of us are extreme larks or extreme owls, most of us lie on a continuum.

{ Fragments of Truth | Continue reading }

photo { Steven Meisel }

Campion was an ophthalmologist […] He became a testosterone doctor. […] The initial session costs $5,000, and the monthly charges are over $1,000. Clients get their blood work done every three months, so that Campion can keep tabs on how their “hormonal balancing” is going. Most patients lock into a permanent testosterone regimen, as Campion has. “I will take testosterone for the rest of my life,” he says. […]

Testosterone can be manufactured cheaply in large quantities, and the risks seem manageable for most people. Users report increased energy, more muscle mass, decreased body fat, greater sex drive, and a general sense of well-being. In short, it’s one of the most transformative substances a human can take. […]

According to a study by University of Texas epidemiologist Jacques Baillargeon, nearly four percent of men in their 60s are taking testosterone. The number of men between 40 and 64 went up 77 percent from 2010 to 2013 to 1.5 million men.

{ Fusion | Continue reading }

art { Andy Warhol, Eight Elvises, 1963 | The current owner and location of the painting, which has not been seen publicly since the 1960s, are unknown }

Impending fatherhood can lower two hormones–testosterone and estradiol–for men, even before their babies are born, a new University of Michigan study found.

Other studies indicate that men’s hormones change once they become fathers, and there is some evidence that this is a function of a decline after the child’s birth. […]

Expectant mothers experience significant hormone changes throughout the transition to parenthood, but less has been known about the prenatal hormone changes among soon-to-be fathers.

Women showed large prenatal increases in all four hormones, while men saw declines in testosterone (which is associated with aggression and parental care) and estradiol (which is associated with caregiving and bonding). No changes were found in men’s cortisol (a stress hormone) or progesterone (which is associated with social closeness and maternal behavior).

{ EurekAlert | Continue reading }

sculpture { Duane Hanson, Old Man Playing Solitaire, 1973 }

The Male Idiotic Theory (MIT) stipulates that the reason men are more prone to injury and death is simply because they “are idiots and idiots do stupid things“. Despite tons of anecdotal evidence confirming MIT, there’s never been a systematic analysis on sex differences in idiotic risk taking behaviour. Until now.

In a new study published in BMJ, researchers obtained 20 years worth of data from the Darwin Awards to tally up the sex of each year’s winner. For those not in the know, the Darwin Awards are given to people who die in such astonishingly stupid ways that “their action ensures the long-term survival of the species, by selectively allowing one less idiot to survive”. […]

Men made up a staggering 88.7 % of Darwin Award winners in 318 examined cases.

{ Neurorexia | Continue reading }

related { Males are more likely to die than females while in the womb }

Although many studies have reported that women’s preferences for masculine physical characteristics in men change systematically during the menstrual cycle, the hormonal mechanisms underpinning these changes are currently poorly understood. Previous studies investigating the relationships between measured hormone levels and women’s masculinity preferences tested only judgments of men’s facial attractiveness. Results of these studies suggested that preferences for masculine characteristics in men’s faces were related to either women’s estradiol or testosterone levels.

To investigate the hormonal correlates of within-woman variation in masculinity preferences further, here we measured 62 women’s salivary estradiol, progesterone, and testosterone levels and their preferences for masculine characteristics in men’s voices in five weekly test sessions. Multilevel modeling of these data showed that changes in salivary estradiol were the best predictor of changes in women’s preferences for vocal masculinity.

These results complement other recent research implicating estradiol in women’s mate preferences, attention to courtship signals, sexual motivation, and sexual strategies, and are the first to link women’s voice preferences directly to measured hormone levels.

{ Hormones and Behavior }

related { Evidence to Suggest that Women’s Sexual Behavior is Influenced by Hip Width Rather than Waist-to-Hip Ratio }

In his groundbreaking research, Geoffrey Miller (1999) suggests that artistic and creative displays are male-predominant behaviors and can be considered to be the result of an evolutionary advantage. The outcomes of several surveys conducted on jazz and rock musicians, contemporary painters, English writers (Miller, 1999), and scientists (Kanazawa, 2000) seem to be consistent with the Millerian hypothesis, showing a predominance of men carrying out these activities, with an output peak corresponding to the most fertile male period and a progressive decline in late maturity.

One way to evaluate the sex-related hypothesis of artistic and cultural displays, considered as sexual indicators of male fitness, is to focus on sexually dimorphic traits. One of them, within our species, is the 2nd to 4th digit length (2D:4D), which is a marker for prenatal testosterone levels.

This study combines the Millerian theories on sexual dimorphism in cultural displays with the digit ratio, using it as an indicator of androgen exposure in utero. If androgenic levels are positively correlated with artistic exhibition, both female and male artists should show low 2D:4D ratios. In this experiment we tested the association between 2D:4D and artistic ability by comparing the digit ratios of 50 artists (25 men and 25 women) to the digit ratios of 50 non-artists (25 men and 25 women).

Both male and female artists had significantly lower 2D:4D ratios (indicating high testosterone) than male and female controls. These results support the hypothesis that art may represent a sexually selected, typically masculine behavior that advertises the carrier’s good genes within a courtship context.

{ Evolutionary Psychology | PDF }

previously { Contrary to decades of archaeological dogma, many of the first artists were women }

Each month many women experience an ovulatory cycle that regulates fertility. Whereas research finds that this cycle influences women’s mating preferences, we propose that it might also change women’s political and religious views. Building on theory suggesting that political and religious orientation are linked to reproductive goals, we tested how fertility influenced women’s politics, religiosity, and voting in the 2012 U.S. presidential election. In two studies with large and diverse samples, ovulation had drastically different effects on single versus married women. Ovulation led single women to become more liberal, less religious, and more likely to vote for Barack Obama. In contrast, ovulation led married women to become more conservative, more religious, and more likely to vote for Mitt Romney. In addition, ovulatory- induced changes in political orientation mediated women’s voting behavior. Overall, the ovulatory cycle not only influences women’s politics, but appears to do so differently for single versus married women.

{ Psychological Science | PDF }

The microbiome — the kilogram of microbes that each of us carries around — has been shown to be involved in everything from obesity and type 2 diabetes to behaviour and sexual preferences. The composition and effects of the microbiome are very active areas of research, producing results which have challenged the way we think about the evolution and interactions of organisms, including ourselves. In a paper recently published in the journal Science, researchers showed for the first time that the make up of the microbiome differs between the sexes, linking these differences to changes in hormone levels and disease resistance. […]

When female mice were given a testosterone inhibitor along with the bacteria from male mice, the rate of diabetes returned to normal.

“It was completely unexpected to find that the sex of an animal determines aspects of their gut microbe composition, that these microbes affect sex hormone levels, and that the hormones in turn regulate an immune-mediated disease,” said Dr. Danska.

{ Inspiring Science | Continue reading }

photo { Jackie Hardt }

Recent experimental psychology […] suggests that the best leaders — both male and female — seem to have relatively high testosterone, which is linked to decreased fear and increased tolerance for risk and desire to compete, and low cortisol, which is linked to decreased anxiety. Effective leadership is associated with hormone levels, and with this hormone profile, leaders are confident and willing to take risks, but not overly threatened or reactive to stressors. [..]

It turns out these two hormones, testosterone and cortisol, are very touchy, sensitive to social and physical cues and fluctuating a great deal over the course of a single day. As Sandberg mentioned in her book, our research shows that people can change their own hormone levels and behaviors, by “faking it” — by “power posing,” or adopting expansive, open nonverbal postures that are strongly associated with power and dominance across the animal kingdom (imagine standing with hands on hips and feet spread, like Wonder Woman). By holding these postures for just two minutes before entering a high-stress situation, people (both men and women) can increase their testosterone by about 20% and decrease their cortisol by about 25%.

{ Harvard Business Review | Continue reading | Thanks Tim }