Science of Love, Sex, and Babies

Who’s Turned On By Pregnant Women?

Posted in parenting, pregnancy, psychology, science, sex by jenapincott on September 26, 2011

 

Early one evening late in my second trimester of pregnancy, I was standing in the dairy aisle of the grocery store, with one hand on my back and the other over the kicking baby in my distended belly. A young man approached me, initiated a conversation about the World Cup, and, casually, asked me if I’d like watch the game with him that weekend. “You’re pretty!” he whispered. I was shocked.

I wasn’t putting out a sexy vibe. (Not at all.) I had assumed that any male attention I receive in late pregnancy, including that from my husband, would be friendly, not sexual. Why would a man who is not the expectant father think pregnancy is sexy? But then other women told me similar stories about how they got hit on in third trimester. So I decided to look into it, and it turns out that a study on sexual attraction to pregnancy has recently come out.

A team of Swedish and Italian doctors, led by Emmanuele Jannini and Magnus Enquist, recruited nearly 2,200 men who had joined online fetish groups such as alt.sex.fetish and alt.sex.fetish.breastmilk. They presented a questionnaire that asked the respondents questions about their preferences for pregnant and lactating women. The survey also asked for the sex and age of each sibling, and whether the sibling is a full sibling or not (half-sibling or adopted child). Most respondents reported both a pregnancy and a lactation preference. The average age at which respondents became aware of their preference was about 18 years.

What Jannini and Enquist and their colleagues were searching for was evidence that there was something special about the upbringing of men that are secually aroused by pregnancy. They knew that a specific stimulus early in life can elicit sexual behavior when theat animal reaches sexual maturity. For instance, goats that are raised by sheep are sexually aaroused by sheep only. This is called sexual imprinting.

Is it possible that boys that are raised by women who are pregnant for much of their childhoods are unusually attracted to pregnant women?

It turns out, what’s good for the goat is good for the guy. The more exposed a man was to his mother being pregnant and breastfeeding when he was between 1.5 and 5 years old, the more likely he is, as an adult, to be sexually attracted to pregnant and breastfeeding women.

A younger sibling is the key to early exposure. The respondents who eroticized pregnancy and breastfeeding had significantly more younger siblings than expected by chance. Respondents with one sibling were older than their sister or brother in 66 percent of cases. Interstingly, siblings born of a different mother does not appear to be related to respondents’ sexual preferences. Only a boy’s own pregnant mother seemed to leave a sexual imprint.

Freud’s “oedipal phase,” from about 3 to about 5-6 years of age, only overlaps partially with the sensitive period suggested by this study’s data, the researchers are careful to point out. Sexual imprinting is different in that it’s motivated not by sexual drive but because the individual learns what’s normal during a sensitive phase of development and later seeks sexual partners that resemble his (or her) own parents.

What does this mean for women who are pregnant or plan to be pregnant? It means you may be able to predict how attracted your partner will be to you in late pregnancy. Does he have sibling born within five years after him? If so, he’s likelier to be turned on by your pregnant self.

As for the guy I met in the dairy aisle, I’d wager he had a younger brother or sister. I’d bet more on getting this right than the winner of the next World Cup.

 *If you like this blog, click here for previous posts and here to read a description of my most recent book, Do Gentlemen Really Prefer Blondes?, on the science behind love, sex, and attraction. If you wish, check out my forthcoming book, available October 11,  Do Chocolate Lovers Have Sweeter Babies?: The Surprising Science of Pregnancy. 

 

 

 

Assorted Trifles (from the science of love, sex, and babies)

Posted in news, parenting, pregnancy, psychology, science, sex by jenapincott on August 4, 2011

Research is like a box of chocolates; you never know what you’re going to find. An assortment of studies on love, sex, and babies — fresh from the lab.

Scientists found that men whose ring fingers are longer than their index fingers are likelier to have longer-than-average penises, at least among Korean men whose flaccid genitals were stretched under anesthesia. Studying the files of women who were raped in 1999-2006, French researchers discovered that there were fewer incidences of living sperm than in rape victims in previous generations, which supports the theory that sperm quality is declining. Women are likelier to get pregnant if they ovulate from their right-side ovary, visible by ultrasound, especially after two consecutive left-side cycles, inspiring women undergoing fertility treatment to desire a L-L-R pattern. Among women whose fetuses inexplicably died in third trimester, 64 percent (392/614) had a premonition before their doctors told them. They described a feeling of discomfort, of a strange unease; that they understood subconsciously that the baby would die. Many described how they dreamed of dead relatives and of death on the night the baby probably died. A recent fMRI study reported that women who had given birth vaginally exhibited greater activation in brain regions involved in the regulation of empathy, arousal, motivation and reward circuits in response to their baby’s cries compared to those who had not. Women who snore loudly and frequently were at high risk for low birth weight (relative risk = 2.6 [95% confidence interval = 1.2-5.4]), and fetal-growth-restricted neonates. The success of an IVF transfer may in part be predicted by how much glucose medium an embryo “eats” on days 4 and 5. On Day 4, female embryos consume significantly more sugar than males.

Do Flame Retardants Make Us Dimmer?

Posted in parenting, pregnancy, psychology, science by jenapincott on July 6, 2011

When I was in the second trimester of pregnancy, my husband and I bought a new king-sized mattress.  Like all cotton mattresses sold in the U.S., ours had been treated with a flame retardant containing polybrominated diphenyl ethers (PBDEs) and/or organohalogen compounds (OHCs). Flame retardants are also in pillows, car and airplane seats, drapes, rugs, and insulation. They’re in electronic equipment, like TVs, and in the dust on top of TVs.  They’re in air and soil and breast milk.  Almost all humans have flame retardants flowing through their veins.

             Around the same time I got my new mattress (on which I tossed and turned in third trimester), two surprising studies were published on the effects of flame retardants on fetuses and young children.

Study #1

A group of researchers at the University of Gronigden in the Netherlands recruited nearly 70 pregnant women in third trimester, taking samples of their blood and measuring it for PBDEs and OHCs. Five years later, the children were given standardized developmental tests for motor skills (balance and coordination), cognition (intelligence, spatial skills, control, verbal memory, and attention), and behavior.

The result:  PBDEs were correlated with worse performance on fine motor tasks and a shortened attention span.  Strikingly, they were also linked with better coordination and visual perception, as well as better (more placid?) behavior.  OHCs, meanwhile, were correlated with worse fine motor skills. Oddly, these kids had better visual perception.

 Study #2

 Researchers at Columbia University tested for PBDEs in the cord blood of nearly 400 women who delivered their babies at a New York City hospital.  These children were given mental and motor development tests in infancy and, later, at four-to-six years. These tests measure memory, problem solving, habituation, language, mathematical concept formation, and object constancy.  They also assess ability to manipulate hands and fingers and control and coordinate their movements.

 The result:  At both age intervals, children who had higher cord blood concentrations of PBDEs scored significantly lower on tests of mental (lower IQ) and motor development.  This was particularly evident at age two for motor skills and age four for IQ (nearly 8 points lower for certain PBDEs).

 

            Are flame retardants slowing us down? Correlation is not causation, but there’s a real risk that they do — and researchers have some ideas about how these chemicals have a toxic effects on the brain. OHCs (for instance) have been found to decrease a fetus’s production of thyroid hormone by interfering with thyroid receptors. This leads to an increase in thyroid stimulating hormone (TSH). Brain development in the fetus relies on the precise timing and quantity of thyroid hormone; too much or too little causes developmental delays. High prenatal exposure to TSH is associated with lower IQs – 4 points less on average.  During critical developmental periods, PBDEs and OHCs may also have a toxic effect on neurons in the hippocampus, the memory region of the brain, by reducing the number of neurotrasnmitter receptors.

            Infants and toddlers have what researchers call a high “body burden” of flame retardants. Household dust, which floor-playing infants and toddlers encounter constantly, accounts for 80-93 percent of postnatal PBDE exposure, followed by breast milk (however, the benefits of nursing appear to outweigh this drawback; breastfed babies score higher on neurodevelopmental tests). 

            A disturbing fact is that American kids have levels of PCBEs that are 10 to 1,000 times higher than their peers in Europe or Asia. We produce 1.2 billion pounds of the stuff annually. (Interestingly, the Scandivanian study, whose subjects had lower levels of prenatal exposure, found no IQ deficit while the U.S. study did.) Consider our nation’s problems:  attention deficit disorder, placidity, lower standardized test scores in reading and math.

Are flame retardants making kids dimmer?

            The question fires up the imagination.  Should pregnant women be advised to avoid, say, dusting and buying new mattresses in the same way we avoid emptying the litter box (to avoid toxoplasmosis)? Are the perceived gains in visual perception real, and, if so, why, and do they come at the expense of other abilities? Are urban kids at a higher risk  than average? Are there naturally flame-retardant materials that we can use in lieu of chemicals?   More research, especially on American kids, is warranted.

            After all, the nightmare scenarios can keep an expectant mom up all night, tossing and turning on her nonflammable mattress.

 

 * If you wish, check out my forthcoming book, Do Chocolate Lovers Have Sweeter Babies: The Surprising Science of Pregnancy. 

 

Are Men Likelier to Cheat When Their Partners are Pregnant?

Posted in parenting, pregnancy, psychology, science, sex by jenapincott on June 13, 2011

It’s bad enough that  Congressman Anthony Weiner had been taking photos of his naked self and sending them to women who weren’t his wife.  It’s worse when we learn that his wife is three months pregnant.

Aha, that it!, some cynics claim.  Now that Weiner’s oats are sowed, he’s exploring new (and, if the twittering teen rumor is real, very green) pastures.  It’s only natural.

But is it?  Are men really more likely to cheat when their wives are pregnant?

Turns out, the answer is that it depends on the man.

Reviewing the studies of pregnancy and sex, it seems there are three categories of expectant fathers. 

  • Type Z cheats or wants to cheat (the Weiners). 
  • Type Y desires his pregnant wife more than ever.
  • And then there’s Type X  — a man who has a decreased sex drive and a lower risk of cheating on his wife.

The bad news is that at least one study found that, yes, the risk of a given man to cheat on his wife increases during pregnancy, even if he is otherwise satisfied in his marriage.  His reasons? He may feel ambivalent about the pregnancy or the changes that go with it. His partner, especially in her first and third trimesters, may not feel like having sex.  Her sex drive may diminish. She may think her body is unattractive.

(Incidentally, bodily dissatisfaction happens to be the number one reason why most women have less sex during pregnancy.  Most of us think pregnancy is a turn-off for men.  That’s a misconception.)

But here’s the good news for pregnant women.  Fact is, many men — the majority as found in this study — desire their pregnant partner even more over the course of the pregnancy, even if they aren’t having as much sex as before. They find her as physically attractive as she was prepregnancy, if not more so. These are usually the Type Y guys. Another study found that, while couples had sex less frequently in third trimester, the only circumstances under which men change their sexual behavior is if they are older or worried about the safety of the fetus. (Note:  Sex does not raise the risk of miscarriage in pregnancies that are not high risk.) Otherwise, men desire sex with their wives just as much.

From an evolutionary perspective,this makes some sense.  Women benefited from having their mates around to help support them through pregnancy and childrearing. Sex helps men stick around.

The Type X expectant father – the one with a low sex drive and a lower risk of infidelity – may overlap with Type Ys. These are men who, at some point over the nine months, are afflicted with pregnancy symptoms:  nausea, weight gain, mood swings, fatigue, even vomiting. Hormones are the culprit.  These men have higher levels of prolactin, a hormone associated with sluggishness, weight gain, and bonding and parental behaviors.  Their testosterone levels plummet, making them less combative and sexually aggressive.

There’s an upside to Type Xs. It turns out that these faithful, fattening men display the most fatherly behavior when the baby arrives.  As new dads, they’re more likely to hear and respond to their infant’s cries.  They’re more compassionate and tolerant.  They make better fathers.

One might speculate that Weiner’s Type-Z behavior while his wife is pregnant doesn’t bode well for Weiner’s fathering instincts. It’s clear that if any hormone is raging in the man, it’s testosterone — not prolactin. He is probably not sharing his wife’s morning sickness and taking turns with her over the toilet.

There’s no crime in what Weiner has done; he’s just another politician more interested in power more than paternity.  But he is making us a little nauseous.

 *If you like this blog, click here for previous posts and here to read a description of my most recent book, Do Gentlemen Really Prefer Blondes?, on the science behind love, sex, and attraction. If you wish, check out my forthcoming book, Do Chocolate Lovers Have Sweeter Babies: Exploring the Surprising Science of Pregnancy. 

 

Why are Redheads More Sensitive?

Posted in psychology, science by jenapincott on April 16, 2011

Redheads may be hotheads, but they get colder faster. They also bruise more easily. And they feel more pain.

All this comes from a series of studies done in the last few years on people with genes for red hair. A true redhead produces an abundance of a yellow-red pigment called pheomelanin. (Brunettes produce the more common eumelanin, a dark brown pigment.) A redhead’s prodigious pheomelanin output is the result of mutations, or variants, of the MC1R.3 gene. Redheads have two copies of this variant allele, one from each parent.

So what does this “redhead gene” have to do with sensitivity? The same gene is involved in the body’s perception of pain. Edwin Liem, an anesthesiologist at the University of Louisville, suspects that when both copies of the MC1R.3 gene are variants, as they are in redheads, receptors in the nervous system modulate pain more intensely.  It’s also possible, according to Liem, that the redhead version the MC1R gene also directly affects hormones that stimulate pain receptors in the brain.

In one study, Liem and his colleagues compared the pain tolerance of sixty naturally red-haired volunteers with sixty brunettes. The redheads reported that they felt a chilling pain at around 6 degrees C (43 degrees F), unlike the volunteers with dark hair. Brunettes did not feel an aching chill until the temperature approached freezing.

In another experiment, also led by Liem, women with various hair color types were exposed to electric shock. Turns out, the redheads needed about 20 percent more anesthetic to relieve the pain (confirming the common belief among anesthesiologists that redheads are tough to knock out). While redheads have normal blood counts and coagulate blood the same as anyone else, they bruise more easily. Yet another study found that redheads are more than twice as likely as women with other hair colors to fear and avoid the dentist.

These studies have been done on women only, and it’s unknown whether red-haired men would have the same outcome. (However, there’s evidence that pain pathways differ between the sexes.)

Redheads are stereotyped as being hot-headed, tempestuous, dramatic, high-strung. Is it possible that a genetic sensitivity to pain can affect temperament? It’s fun to speculate. For some, physical pain may translate into emotional pain. Sensitivity may tip over into volatility. Could a fiery, short temper even be a pain avoidance mechanism? Why not–after all, a good offense can be the best defense.


Why are Men Mad About Mammaries?

Posted in news, psychology, science, sex by jenapincott on April 3, 2011

Why do men love breasts?

Let me count the theories:

1. Freudian (breasts remind men of their moms and the nurturing of childhood)
2. Evolutionary (breasts resemble buttocks, and prehuman ancestors always mounted from behind)
3. Reproductive (breasts are an indicator of age, and big breasts in particular are a marker of high estrogen levels, associated with fertility).

Do these reasons sufficiently explain why breasts are beloved — even in cultures that don’t eroticize them any more than the face?

If not, here’s another:

Breasts facilitate “pair-bonding” between couples. Men evolved to love breasts because women are likelier to have sex with — and/or become attached to — lovers who handle their breasts.

This idea came up in New York Times journalist John Tierney’s interview with Larry Young, a neuroscientist famous for his research on monogamy. According to Young, “[M]ore attention to breasts could help build long-term bonds through a ‘cocktail of ancient neuropeptides,’ like the oxytocin released during foreplay or orgasm.”

The same oxytocin circuit, he notes, is activated when a woman nurses her infant.

When women’s breasts are suckled, as they are during breastfeeding, the hormone oxytocin is released. Oxytocin makes the mother feel good and helps her bond with her baby. She feels loving and attached. The same reaction might happen if a man sucks and caresses a woman’s breasts during foreplay. In our ancestral past, the most titillated men may have been the ones to attract and retain mates and pass on their genes.

The “boobs-help-bonding” theory may not be the strongest explanation of why men love breasts, but it’s worth introducing to the debate. That said, there are many ladies out there for whom a lover’s suckling does nothing — and there are many breast-ogling boobs who know nothing of foreplay.

Do Brothers Stall Their Sisters’ Sex Lives?

Posted in parenting, psychology, science by jenapincott on March 20, 2011

Nearly eight months ago I gave birth to a baby girl. The child is now a seam-popping twenty-plus pounds. Infants, they grow so quickly it’s creepy — my thoughts fast-forward through her teething years to the teens, and I’m terrified. Problem is, my family lives in New York City where children want to be adults. The weenies of tweens should stay in their jeans, but all too often they don’t.

The onset of girls’ sexual maturity depends a lot on the social environment — peers, culture, and so on. A recent study by Australian behavioral ecologists Fritha Milne and Debra Judge found that it especially depends on the family environment, and not in the expected ways of curfews and chastity pledges. Sure, if you’re a teenage girl your parents might hold you back from trying to lose your virginity. So may your grandparents and any other authority figure in your family.

But so might your little brother.

Milne and Judge recruited nearly two hundred women and seventy-six men, all living in or around the city of Perth, Australia, and asked them questions about their family lives and sexual development. The results were that girls with only younger brothers lost their virginity an average of more than a year later (at age 18.3) than girls with younger sisters only. Girls with both younger brothers and sisters lost it nearly two years later on average (age 19.3) than girls with no younger siblings. Younger sisters alone had no impact.

The chastity effect only applied to girls with younger brothers. Having a big brother (or sister) didn’t make a girl any less likely to hold onto her virginity, yet another strange pattern emerged. This one involved the girls’ physical maturity.

The more older brothers a girl had, the later she got her first period. Girls with only elder brothers got their first visit from “Aunt Flo” up to a year later (at age 13.6) than girls with older sisters or no older siblings (age 12.7). (This is meaningful given that breast cancer and other conditions are related to earlier menstruation.)

Elder brothers delay physiological maturation, while younger brothers delay behavioral maturation.

What’s going on?

Trained as behavioral ecologists, Milne and Judge took a look at the big picture. Daughters are often caregivers. Historically, as has been found in traditional societies, a woman with daughters as first- or second-born children has a larger family than a mom whose first children were sons. Elder daughters take care of younger siblings, which frees up Mom to keep popping them out. Boys historically required more resources than do girls, which made big sister’s contributions even more important. As a result, these helpful elder daughters experience a delay in starting their own families. In the modern world where women don’t usually start their families until their mid-twenties on average, this is no problem, but in the past females with brothers may have had fewer children over their lifetimes.

The bigger mystery is what’s actually behind Big- and Little Brother’s stalling effect on their sisters’ sexuality. This is unknown territory, so Milne and Judge tread lightly here. The safest theory is that the delays are behavioral. Girls with little brothers lose their virginity later because they’re too busy taking care of their siblings to have love lives of their own. Perhaps little brothers, who are slower than female siblings to develop and reach puberty, keep their elder sisters in a more childish mindset. Or perhaps the stress of care-giving slows down puberty.

The researchers should also consider a much more surprising yet equally plausible theory: brothers send out chemical cues (pheromones) in their sweat that inhibit their sisters’ sexual development. Odd as it sounds, this would explain the perplexing finding that girls with older brothers get their first periods later than their peers. And, it appears, so do girls who grow up with their biological fathers in the household, compared to their peers with absent dads. Several studies, including here and here and a large one at Penn State that involved over nineteen hundred college students, came to this conclusion. (Interestingly, the same study found that girls growing up in homes with males unrelated to them got their periods earlier than average.)

The sweat-stifles-sexuality theory isn’t as far-fetched as it sounds. Other animals — rodents, for instance — use pheromones to modulate sexual maturity and fertility in a population. Over the years, a girl would inhale chemical cues in fraternal sweat — think of all those sock and armpit odors. Those chemicals would hit the hypothalamus of her brain where sex hormones are produced, and slow down the works. Puberty strikes a little later. Evolutionarily speaking, the result is that a girl could stay in the family nest longer without conflict. The risk of incest is reduced.

So should I try for son now? Truth is, the data applies to populations, not individuals. There are no guarantees; these are just interesting findings that deserve more research. Moreover, I’m in over my head right now with my baby girl’s teething and feeding challenges. Sure, I’ll want preserve her girlhood for longer than a New York minute. But I also need to preserve my sanity

 

Do baby tears have mind-control properties?

Posted in news, psychology, science, sex by jenapincott on March 8, 2011

A few weeks ago, Israeli neuroscientists Shani Gelstein and Noam Sobel published a study about mind-control properties in human tears. The gist of the research, which enjoyed much media attention, is that women’s tears contain a chemical signal that reduces sexual desire in men. Tears were collected from the cheeks of emotionally-distraught women watching sad films and wiped on the upper lips of male volunteers. Compared to men who whiffed a salt solution control, the tear-sniffers not only had a reduced sex drive but also lower testosterone levels and reduced brain activity.

A leading explanation is that chemicals in tears generally reduce male aggression, making them more sympathetic.

How does this work? One theory is that one or more of the hundreds of chemicals in tears has “mind-control” properties, triggering specific predictable behaviors in others. (Here and here I write about how this happens in sweat, too.) One candidate is prolactin, a hormone associated with bonding. When inhaled in a person’s tears, prolactin may affect the sniffer’s hypothalamus, the part of the brain that produces hormones which in turn affect behavior.

Baby tears have not been the subject of a study yet (hopefully soon). But it’s not a far cry from certain that if there are chemicals in the tears of women that affect men, there are also chemical triggers in the tears of babies that affect their caregivers or anyone else that comes into contact with them. These tears may trigger care-giving instincts and reduce aggression toward the screaming infant.

I wonder: Infant abuse is relatively uncommon given how irritating a screaming baby can be. Are the people guilty of this crime more likely to be amnosiacs (loss of smell-sense) or have another form of brain damage that would prevent them from inhaling aggression-reducing signals in the baby’s tears?

Another theory: Kids cry all the time and sometimes it’s hard to tell when they really need attention. Might chemicals in emotional tears direct parents to respond appropriately when there is a real need for attention? Assume these chemical signals are only in emotional tears–not crocodile tears or sleepy-time tears. Do they help us intuitively know when it’s OK to let a child cry it out instead of rushing to soothe her?

Perks and perils of the Pill?

Posted in news by jenapincott on August 7, 2010

I spoke to the blogger Rachel Rabbit White about the psychological impact of birth control, and here’s her article.

On a personal note, I’m busy with a newborn so posts will be (temporarily) less frequent…..

“Cheating gene” mouth swab test available

Posted in news by jenapincott on May 8, 2010


In BLONDES and in this post I write about the so-called “cheating gene.”

Not long ago, Hasse Walum, a handsome post-graduate at the Karolinska Institute in Sweden, decided to study the association between a particular gene for what is called a vasopressin receptor and relationship stability. He analyzed the responses of over 550 twins and their partners to questions, some of them intrusive, about their relationships: How often do you kiss your mate? “Have you ever regretted getting married/moving in?” “Have you discussed a divorce or separation with a close friend?” “Rate your degree of happiness in your relationship on a scale of 1-7.”

Walum then sampled the men’s DNA. Getting DNA from the men was simple. You don’t need blood to have access to another person’s genome, just saliva, which the men submitted in a mouth swab.

What Walum discovered was stunning. Focusing on one particular vasopressin receptor gene variant, allele 334, he found that the more copies of it a man had, the weaker his bond with his partner. Men who lacked the gene variant were generally happiest in their relationships — only 15 percent of them had a crisis. Men with one copy were slightly more likely to have marital problems. And men with two copies were, on average, twice as likely to have had a relationship crisis in the past year than men who didn’t have the variant — meaning that 34 percent of them, or one in three, were headed toward a break up. Their partners agreed. Women whose partners carried one or two copies of the allele 334 variant were generally less satisfied with their men, probably because they generally scored as less affectionate than other guys.

Walum also found that men with two copies of the variant were nearly twice as likely not to marry their partners and mothers of their children as men who had no copies of the variant. This suggests that there is something slightly different about the vasopressin receptors in the brains of men who struggle in their roles as partners and fathers. These men may have more difficulty bonding with other people, including their wives and kids.

I imagine that some of you are now scheming to get an allele 334 test for your man. Of the more than five hundred women who responded to my online poll on this topic, nearly 65 percent said they would test their man if given the option.

And now you can. Yes, you can order a saliva test for allele 334 of the AVPR1A gene for $99 from Genesis Biolabs. (I can’t vouch for the lab. I’m reporting for entertainment purposes.)

Ladies, there’s a caveat here, of course. Even if there’s a correlation between this particular gene variant and a man’s behavior, it doesn’t account for all men. Just as the “god gene” and “gay gene” are met with skepticism in the scientific community, so is the “cheating gene.” Even within Walum’s study, there were men with two allele 334 variants who were happy husbands and fathers, and there were men without the variant who were miserable in their relationships. The statistics apply to populations, not individuals, who are also influenced by a other factors — parental role models, partner choice, opportunity to cheat, past loves, age, life satisfaction, religion, hormone levels, and so on.

A two-allele man may become a number one husband under the right circumstances.

But it’s your call. Swab him and then decide?

How could you possibly be pregnant and not know it?

Posted in pregnancy by jenapincott on April 10, 2010

Now at the start of third trimester, I find it inconceivable that there are women at this stage — and beyond — who still do not know they’re pregnant.

Here are the astonishing statistics: 1 in 455 women doesn’t know she’s pregnant until after week twenty, and 1 in 2,500 is oblivious until she actually goes into labor. The latter are known to give birth, without medical assistance and in agonizing pain, in Walmart bathrooms and at proms, in dorm rooms and in their own bathrooms. They had no idea they were pregnant because they had irregular periods, have been on birth control pills, are in perimenopause, have had menstrual-like bleeding, and/or are overweight and less sensitive to weight gain.

But I know what you’re thinking because I’ve thought it too: it’s denial. On some level the ladies must’ve known they were pregnant but couldn’t deal with the reality.

Yet the more I explore the origins of cryptic pregnancy, as the condition is clinically called, I realize that denial or mental illness doesn’t explain most of the cases. Only a minority of cryptic pregnancy cases has been attributed to personality disturbances (8 percent) or schizophrenia (5 percent). It appears that most of these women are perfectly sane, educated, and in stable relationships. Quite simply, they do not know they’re pregnant because they have no symptoms — no weight gain, no nausea, and little to no abdominal swelling. Or the symptoms are so subtle as to be easily mistaken for something else.

Every pregnancy is a tug-of-war of resources between Mom and fetus. Each has her self-interest in mind. Most of the time the tug-of-war ends up in a happy equilibrium. Mom provides enough nutrients, but not too much too handicap herself. But sometimes Mom gets more rope….at the expense of the fetus.

According to evolutionary psychologist Marco Del Giudice this might happen in a few ways. For one, the fetus might not be putting out enough signals that it exists and needs resources. One way fetuses announce their existence is through HCG, the hormone that makes a home pregnancy test turn positive. In many cases, the higher the HCG, the more severe the morning sickness and other symptoms. A baby that produces a scant amount amounts of HCG might go “under the radar,” failing the pregnancy test and going unnoticed by the mother — physiologically and psychologically. This would mean the baby gets fewer resources than she otherwise would. The lack of HCG signaling in cryptic pregnancies explains why these babies are so often born preterm, underweight, and small for their gestational age. They didn’t ask for more resources from Mom, and they didn’t get any.

There are a few reasons why a baby wouldn’t produce enough HCG. One is chromosomal anomalies; that is, the fetus has a birth defect and is in danger of miscarrying. It’s also possible that an otherwise healthy fetus simply puts out low quantities of the hormone due to a genetic quirk.

Or, here’s an interesting theory: Maybe Mom has stress and relationship problems. In this case, biologically speaking, it may be in the fetus’s best interest for the mother to be completely oblivious to the fact that she’s carrying to prevent being rejected and miscarried, which may happen when a woman is stressed. As Del Giudice points out, in our evolutionary past a woman who did not know she was pregnant and had few to no symptoms could conserve precious energy. She would be able to move freely and eat food of any kind, and as a result be better able to survive in the face of stresses and threats. In this case, babies may put out less HCG or stressed-out moms may unconsciously lower their sensitivity to the hormones.

Seen this way, cryptic pregnancy is an adaptive “emergency” mechanism — essentially, the fetus sensing a threat and striking a bargain with the mother by demanding little and laying low. When the normal stresses of pregnancy might otherwise trigger a miscarriage, this “stealth strategy” allows the fetus to survive.

The case for wearing blush

Posted in news by jenapincott on January 24, 2010

Bad news for pale girls like me: red is hot. Not only do studies find that men are more attracted to women in red, now we find that men prefer women who are red. Their cheeks, that is….

In a new study, evolutionary psychologist Ian Stephen and his colleagues at the Face Perception Lab recruited volunteers of various races and asked them to digitally adjust the color tone on more than 50 faces to make them look as healthy and attractive as possible. Volunteers consistently added more red coloring to the cheeks — whether the face was Caucasian, Asian, or Black. The redder the face, the more suggestive it is of oxygen-rich blood reaching the skin. The more oxygen-rich blood, the more suggestive it is of the person’s general health and youth. An old person, a sick person, a person with hypertension or bad circulation…will not get rosy-cheeked.

And not only is a flush suggestive of good health and fitness….but high sex hormones as well. In women in particular, high levels of estrogen may cause an expansion of tiny blood vessels under the skin. Hence, rosy cheeks. As in monkeys, female facial redness may be associated with fertility and reproductive quality.

As Stephen points out, the human eye has evolved to pick up on fine variations on the color red. “People are sensitive to the subtle color difference between oxygenated and deoxygenated blood (oxygenated blood is a bright red colour, deoxygenated blood has a slightly bluish red colour, and we interpret this difference in skin blood oxygenation colour as a cue to the health status of individuals.”)

But why did the researchers find that volunteers preferred women over men with rosy cheeks? One reason may be the sex hormones, which show up more obviously in flushed female faces. But it may also be due to the fact that men already have ruddier faces than women do — they have higher levels of hemoglobin and arterial oxygen content in their blood. As a result, the male blush is not as obvious a cue of good health and high sex hormones.

There are surely other reasons why a maidenly blush is attractive, as I describe in BLONDES. For one, a flash of color to a woman’s cheeks may suggest youth, modesty, embarrassment, excitement…all of which, depending on context, may appeal to red-blooded men.

Do hypochondriacs prefer macho men?

Posted in news by jenapincott on January 8, 2010

Evolutionary psychologists tell us that one of the reasons why women find masculinity attractive is that high testosterone is a sign of a strong immune system. A strong immune system, in turn, in a sign of good genes and childhood development (testosterone is an immunosuppressant and only men with good genes can overcome its drawbacks). These strong square-jawed macho men aren’t necessarily good dads: they’re more likely to be uncooperative, combative, and aggressive. But they may offer good genetic material for your kids, depending on the circumstances.

So how do you prove that women equate masculinity with good genes and healthy immune systems (subconsciously, at least)? An indirect approach was taken by Lisa DeBruine and her colleagues at the Face Research Lab at the University of Aberdeen. (The Lab conducts many fascinating studies on attraction, some of which I reference in BLONDES.)

In this new study, DeBruine recruited 345 women of all ages to rate faces. The faces were digitally altered, and ranged from very masculine to very feminine. Participants also completed a test called the Three-Domain Disgust scale, designed to measure moral disgust (deceiving a friend), sexual disgust (hearing strangers have sex), and pathogen disgust (stepping on poop).

Turns out that women’s preference for masculinity in male faces was correlated with disgust sensitivity to pathogens, but not in the moral and sexual domains. (Yes, hypochondriacs do prefer macho men!) DeBruine speculates that in certain situations, such as disease-ridden environments, women are wired to prefer high-testosterone males. The benefits of their good immune system genes are worth the tradeoff.

The testosterone-means-good-genes theory, anyway, may explain why women in disease-ridden environments are likelier to choose macho guys. Explains DeBruine et al.:

Because a partner’s heritable health is of greater value when pathogens are a greater concern, concern about pathogens is likely to also be a factor that contributes to the resolution of this tradeoff. Cross-cultural differences in mate preferences and mating systems vary consistently with differences in pathogen prevalence. When people from 29 different cultures were asked to rank a series of attributes based on how important they would be in a mate, people in areas with a high prevalence of pathogens ranked physical attractiveness higher than people in areas with a relatively low prevalence of pathogens did. Also consistent with these
findings, rural Jamaican women prefer masculinity more than British women do…

So do hypochondriacs, fearful of disease, marry more macho men (e.g. self-professed hypochondriac Susie Essman and her new husband?) As environments become more sterile, will we prefer men with softer, sweeter faces and personalities? Or will the next swine flu outbreak inspire us to pursue pigs?

When the perfect woman is genetically male

Posted in news by jenapincott on June 1, 2009

42-20487063Years ago, in college, I met the perfect woman. Or perhaps a man’s idea of the perfect woman. She had flawless and dewy skin, angular cheekbones, a cinched waist, milkmaid breasts, long legs, dove-like hands, lush long hair. Wherever she went, people swiveled their necks and stared. She was a fantasy, a vision. A goddess.

And she was miserable.

It emerged that the source of her pain was a secret that she kept until she enrolled in a radical gender studies class. Inspired, she came to terms with her identity, and in the telling she liberated herself. Her secret was that she wasn’t technically female. She had a condition known as androgen insensitivity syndrome (AIS). She was the perfect woman on the outside, and inside she felt perfectly female. But she was genetically male (XY).

Her story was typical for women with complete AIS. At birth her doctors didn’t notice any difference in her genitalia. In high school she went from being a normal girl to an Amazonian queen. She was not only taller than her peers but curvier, too (some androgens are converted to estrogen which act on breast tissue). Unlike other girls, she never got acne or grew pubic or armpit hair (androgens regulate hair growth). She had no body odor. She got recruited as a runway model, was attracted to men and had many boyfriends (including a celebrity), and had sex, albeit painfully. But by age sixteen she didn’t get her period, so her mother brought her to the doctor and an astonishing discovery was made. She had undescended testes. Inside, she appeared male: no fallopian tubes, no uterus, no ovaries.

This gorgeous college student had complete androgen insensitivity syndrome. Women with this condition — approximately 1 in 20,000 — tend to be exceptionally tall and striking in appearance. AIS is caused by a recessive variant of the gene that codes for Androgen Receptor. Because the body is insensitive to the androgen testosterone, the usual male features — penis, testes, scrotum, etc. — are unable to develop. The default phenotype is female, so people with AIS have a vagina or “vaginal pouch” (although most AIS women require surgical expansion). If a woman with AIS were to get a blood test, her testosterone levels would be as high as any man’s, but her body can’t process the hormone. That’s why women with complete AIS are so feminine — arguably more so than other women. (Some people with AIS have only partial androgen insensitivity. Considered intersex, or hermaphrodites, they fall all along the spectrum between typically male and female and have a micropenis. Naturally, there’s much controversy about gender assignment at birth and estrogen or testosterone injections at puberty.)

Several women have revealed they have complete or partial AIS, including singer Eden Atwood and tennis player Sarah Gronert. Although impossible to confirm, several famous celebrities of the past are purported to have had AIS: Wallis Simpson (Edward may have given up the crown for her, but it is said they could never have sexual relations), Queen Elizabeth I, and Joan of Arc. Rumors of AIS abound, perhaps out of jealousy, whenever a celebrity is statuesque, beautiful, and lacking a biological child — Jamie Lee Curtis, Ann Coulter,and even Gisele Bunchen,among many other model types.

In a sense, complete AIS flies in the face of the evolutionary theory I write about in BLONDES. If straight men are drawn to slim waists, shapely breasts, lush scalp hair, sparse body hair, long legs, and flawless skin because those qualities represent high fertility, then AIS is the ultimate deception. As gorgeous as an AIS woman is, there’s no chance of conception. But this ultimately doesn’t matter. It’s the 21st century, and an important lesson must be learned: Femininity is about more than reproduction.

Hormones in 20 seconds or less

Posted in news by jenapincott on May 16, 2009

The_Notebook_Limited_Edition_DVD-Contest-Ryan_Gosling-Rachel_McAdamsWithin 20 seconds of encountering a beautiful woman, men have been shown to have a surge of two hormones: testosterone and cortisol. This makes good sense, evolutionarily speaking. As I describe in BLONDES, hormones mirror the subconscious mind. Testosterone promotes assertiveness and reflects increased sexual desire. Cortisol focuses motivation. Women are the choosier of the sexes, which means — generally, of course — that the onus is on men to flaunt and flatter or take other action to attract the woman.

But what do women do when they see an attractive man?

The same thing. Far from being passive observers, women also experience a hormonal riot within seconds of seeing a hot guy. This is true even if the man is an actor in a film, as indicated in a new study led by neuroscientist Hassan Lopez at Skidmore College. Lopez and his team showed 120 women one of four 20-minute videos, each with a different scenario: 1.) an attractive man courting a woman (a clip from The Notebook starring Ryan Gosling) exhibiting a dominant social presence, risk-taking, kindness to children, faithfulness, confidence, and humor 2.) a nature documentary about caves; 3.) an unattractive older man (Jack Nicholson) courting a woman 4.) an attractive woman (Cameron Diaz) with no man present. Saliva samples were taken right before and after each viewing.

Of all four groups, only the women watching the hot, desirable, “high mate value” guy trying to seduce a woman had a surge of testosterone and cortisol. The higher the hormones, the stronger the romantic/sexual interest the women reported. (Interestingly, women on birth control pills only experienced a cortisol surge, not testosterone, apparently because the pill suppresses the hormone. Naturally-cycling women also reported a greater willingness to engage in sexual activity and enter a relationship with the attractive man. This may be due to stronger hormonal surges in women who aren’t on the Pill or the fact that more Pill-takers are already taken.)

The study reminds us that hormones help both sexes focus and flirt more effectively, and a surge at the sight of an attractive prospect may change our moods in an instant. But what threshold must be met to trigger such a surge? Do women with higher baseline testosterone and cortisol levels respond faster and get turned on easier? Are high testosterone men more effective in raising women’s hormones? Could taking the Pill really decrease your natural attraction to handsome strangers? And when two people mutually elevate each other’s hormones within seconds, is that considered love at first sight — or just lust?

Why you should gaze into your dog’s eyes

Posted in news by jenapincott on May 9, 2009

2226912113_a02d77537eTo quote George Elliot: “That quiet mutual gaze of a trusting husband and wife is like the first moment of rest or refuge from a great weariness or a great danger.” Locking eyes with a loved one triggers a powerful hormonal response, in particular the release of the hormone oxytocin. The more oxytocin absorbed by receptors in your brain, the more trusting, attached, and calm you’ll feel.

Have no trusting partner with whom to share that “quiet mutual gaze”? Not to worry: a new study led by biologist Miho Nagasawa at Azabu University in Japan has found that much of the same benefit can be gained from your pet dog.

Yes, dogs have been found to increase their owners’ oxytocin levels much in the same way that close human companions do. Nagasawa and his colleagues measured urinary oxytocin concentrations from 55 owners (male and female) just before and twenty minutes after interacting with their dogs. The owners were divided into two groups: those whose dogs gazed at them frequently and extensively (~150 seconds per gaze) during the half-hour interaction, and those whose dogs made less eye contact (<50 seconds). In a control experiment, the owners were forbidden to look at their dogs while interacting with them.

Owners who made extended eye contact with their dogs had significantly higher oxytocin levels in their urine after the experiment than beforehand. Owners who only made brief eye contact with their dog during the interaction didn’t have much of an oxytocin surge. Nor did any of the owners when they weren’t allowed to make eye contact with their pets. Duration of ownership and the gender of the owner and dog were ruled out as significant factors.

Oxytocin, conclude the researchers, works just as well for inter-species bonding as it does human bonding. A mutual gaze triggers semiautomatic attachment behavior, and it’s not limited to lovers and babies. The owner perceives an emotion in the animal’s gaze and anthropomorphically interprets it as mutual attachment. When the eye lock is extended and nonthreatening, we’re hardwired to reciprocate in kind (which, as I detail in BLONDES, is why it works so well for lovers). Oxytocin facilitates this bonding effect — and the owner feels emotionally closer and satisfied by the pet in the same way he or she might in a human relationship.

Do dogs get the same oxytocin rush from gazing at their human companion? It’s unclear. While humans gaze at their pets to fill their hearts and souls, our pets might gaze back to fill their stomachs or to establish dominance. But I’m not completely cynical. I have a precious Siamese cat who has been my companion since I was a teenager. She has chronic renal failure now. One of her eyes is a milky gray, the result of a cataract and luxated lens that the vet doesn’t want to fix. She rests on my lap as I write. Once in a while she picks up her head and gazes at me with her one blue eye, and I know she loves me too.

Oxytocin isn’t the only love drug

Posted in news by jenapincott on May 3, 2009

love_drug_sticker-p217913312752479072q0ou_4002In all the media frenzy about the “love drug” oxytocin — a hormone released after sex, when kissing, after twenty seconds of hugging, and so on — we have lost sight of another hormonal cue of closeness and trust: progesterone. Who talks about progesterone outside menopause discussions? In BLONDES I try to give progesterone some credit, discussing it in questions involving movie-watching lovers, female friendship in the luteal phase of the menstrual cycle (after ovulation), and the effect of lactating mothers on the sex lives of their friends.

Progesterone is interesting because it can indicate a person’s motivation to bond with others.

The higher your progesterone levels, the greater your “affiliation motivation” – that is, the satisfaction you derive from positive relationships with others. In women, progesterone levels are higher after ovulation and during pregnancy. Women on oral contraceptives have been found to have higher levels of “affiliation motivation” than men and women who don’t take birth control because the Pill contains progestins. Progesterone may also give oxytocin a boost by increasing the number of oxytocin receptors in the brain. People with high levels of progesterone rate their friends, family, and long-term partners as more attractive than do people with lower levels of the hormone. From an evolutionary perspective, progesterone is one of those hormones that helps you trust, bond with, and identify with others — and even put another person’s well-being above your own.

This theory was put to the test in a hot-off-the-press study led by neuroscientist Stephanie Brown at the University of Michigan. Brown and her colleagues recruited 160 women, paired them up, and assigned each pair to one of two groups. Pairs in Group 1 were told to play a “closeness game,” which involved asking each other questions such as, “What the greatest accomplishment of your life?” Pairs in Group 2 were told to proofread an article together and try to find as many errors as possible. Following this, everyone filled out a test that assessed closeness and — astonishingly — willingness to risk one’s life for the partner. The women then were assigned to play a cooperative card game (the idea is to win by working together). Before and after each exercise, each participant’s saliva sample was collected and progesterone levels tested. One week later, all the women returned to the lab to play the cooperative game again with the same partner they had the first time.

The results? Unsurprisingly, it turned out that the closeness game induced higher progesterone levels. Women who asked each other personal questions not only had higher progesterone levels after the cooperative game, they also reported a stronger willingness to sacrifice their life for their partner. Progesterone levels among those women who played the “closeness game” were also higher when they returned to the lab for the second round of tests a week later.

Progesterone, the researchers say, is hormonal proof of the positive health effects of meaningful social contact. Does high progesterone drive people to sacrifice their own lives for others? As the researchers point out, the hormone is correlated with this behavior; they can’t yet prove that it causes it. Nevertheless, it’s known to reduce stress and enhance bonding behavior — it’s not a stretch to say that high-progesterone types are more loving and giving.

But what does this mean for romantic love? Further research between potential romantic partners would be interesting. Would the progesterone surge following a “closeness game” lead couples to bond more easily, stress less, and sacrifice themselves more readily? Do relationship counselors now have hormonal proof that couples should ask each other prying questions on dates? Will control freaks start testing their date’s saliva for “affiliation motivation”? (Readily available are home test kits to measure progesterone levels.)

Unlike other potential “love drugs,” lovers are advised against taking progesterone supplements as relationship aids. While the hormone is related to trust and bonding and cuddling, and helps prime the sex drive, an excess is associated with a low libido. Love drug, maybe. Lust drug, not.

Why is your left breast larger than the right?

Posted in news by jenapincott on April 10, 2009

362537232_hskda-m000x0287x450jpeg2 In BLONDES I mention that, for many women, the left breast is slightly — about 4 percent — larger than the right. The factoid was buried in a discussion about sexual selection, the upshot of which is that breasts are a factor even in cultures that don’t eroticize the chest any more than the face. Breast symmetry is one cue of developmental stability, and large and symmetrical breasts suggest “good genes.” That said, yes, it’s normal to have one breast that is slightly larger than the other. The larger your breasts, the more obvious the asymmetry. For about 65 percent of us, the more voluminous one is the left.

But why?

Breast asymmetry is associated with rapid growth spurts prior to and during puberty. It’s normal for one breast to respond more to surging estrogen levels. Hormonal disruptions and other development problems accentuate the asymmetry. But why the left? No one knows for sure, but there are interesting theories:

* The immune system is known to be functionally asymmetrical, and immune hypersensitivity is higher on the left side of the body. It’s possible that enhanced immunosensitivity has an effect on tissue-plumping growth hormones such as estrogen. The immune system may send to the brain information that is asymmetrically expressed. Immune system asymmetry may also explain why cancers occur 5-10 percent more often in the left breast and inflammation associated with herpes zoster affects the left side more than the right.

* Nursing infants may make the left breast even larger. Although studies have not found a link between a larger left breast and handedness, many women report that they prefer having their dominant right hand free while breastfeeding, which means infants more often nurse on the left breast. Favoring the left breast makes it larger.

Personally, I prefer the explanation my friend gave her curious eight-year-old daughter when she saw that Mom’s left boob was bigger: It’s because I have a really big heart under it.

What are “female hormones” doing in semen?”

Posted in news by jenapincott on March 29, 2009

queens2
It happened again to my friend C. — she had an affair with a dashing Moroccan guy two weeks ago and got her period early. She always experiences short or untimely cycles in the beginning of relationships, and do many women I know. One study found that one out of every three gals reports getting her period early in response to a new sex partner, or — as been found among Army wives — a visit from an existing one who lives far away. Even among women whose cycles are like clockwork, novel sex can make them cuckoo.

There are many factors that can throw off a cycle, including emotional excitement and stress. As I discuss in BLONDES, there’s evidence that sweat and semen can, too. Digging deeper into the psychobiology of semen, I stumbled upon a provocative theory. It all begins with the discovery that semen contains “female hormones” including follicle stimulating hormone (FSH) and luteinizing hormone (LH).

Why are these so-called female hormones in semen? The answer, according evolutionary psychologists Gordon Gallup and Rebecca Burch at SUNY Albany, is that they increase the man’s chances of impregnating the woman. Unlike females of other species, women don’t advertise when they’re ovulating. And because ovulation is concealed and the fertile window easy to miss, it may take many months of regular sex for conception to happen.

But what would happen if men could control the timing?

Turns out that hormones in semen may do exactly that — by mimicking the conditions of ovulation. The FSH in semen causes an egg in an ovary to ripen and mature. The LH in semen triggers ovulation and the release of the egg. If a woman is near ovulation — say, in the first week or so of her cycle — these seminal chemicals may be sufficient to induce an early release of the egg. By synchronizing ovulation with sex, a man improves his chances of conception in a casual encounter.

As a reason why female hormones are present in human sperm, the theory sounds plausible. Women conceal ovulation to prevent men from knowing when they’re fertile (for reasons I discuss in the book). Men, in an evolutionary tit for tat, developed ways to induce ovulation to increase the chances of conception. Indeed, when researchers analyzed the sperm of chimpanzees, which advertise ovulation rather than conceal it, levels of the female hormones LH and FSH were low to nonexistent.

Of course, questions remain: How do women’s cycles normalize a few months into the relationship despite ovulation-inducing hormones? Are FSH and LH hormones exclusively “female;” what other purposes might they have for men?

As for my friend C., she didn’t get pregnant from her fling. Fortunately, her cycle only accelerated. But the risk of a surprise pregnancy is one more reason why it’s a good idea to use a condom.

The “psych” in semen

Posted in news by jenapincott on March 25, 2009

hypnotize2My post on mind control properties in semen still attracts a disturbing amount of attention. So to appease your curiosity — and, I’ll admit it, mine — I’ve decided to do a little more investigation into the compounds in semen that may enter the bloodstream after sex. Some may have an indirect effect on the recipient’s hormones. A few may breach the blood-brain barrier, directly influencing mood and sex drive. Several, but not all, of the chemicals have been studied and proven to pass through the vaginal walls. From an evolutionary perspective, mood-modulating components in semen may give a woman an incentive to be in a committed relationship with regular, frequent sex. Apparently, the goo is bonding.

The information below comes from SUNY Albany evolutionary psychologists Gordon Gallup and Rebecca Burch, whose fascinating study on semen and depression I describe in BLONDES. Gallup and Burch wrote a chapter, “The psychobiology of human semen,” published in a compilation of research on sexuality. What they describe, I think, is fascinating.

The primary putative mind-altering ingredients in semen:

Luteinizing hormone: astounding concentration in semen; linked to high sperm count and motility. Absorption into female bloodstream may facilitate or even induce ovulation.

Prolactin: influences maternal behavior, oxytocin secretion; mediates bonding

Estrone and estradiol: assists in recipient’s absorption of other compounds such as progesterone; may boost woman’s sexual motivation and mood

Testosterone: may increase sex drive and motivation; the more intercourse, the higher the testosterone levels in women, and the stronger the sexual desire. More than half the amount of testosterone in sperm has been found to be absorbed by the vagina.

Cytokines: these are the “warriors,” they suppress immune reaction to semen invading the vagina and cervix and therefore increase likelihood of pregnancy

Enkephalins: these opioids may contribute to orgasmic experience. They may decrease anxiety and cause drowsiness after sex.  There’s also speculation that they assist in immune function and “reinforcing effects” — making a woman come back for more, i.e. addiction  (although the absorption rate in female bloodstream is unknown)

Oxytocin: assists in stimulation of ovulation, increases production of other hormones, initiates bonding, facilitates orgasmic contractions; may strengthen bonding and make sexual activity more rewarding

Placental proteins, including human chorionic gonadotrophin (hcg) and human placental lactogen: associated with sperm motility; may increase chances of pregnancy

Relaxin: made in the prostate, this hormone may facilitate fertilization, implantation, and uterine growth. The role of relaxin suggests that women should keep having a lot of sex during pregnancy because sperm has pregnancy-maintaining properties. Relaxin also facilitates implantation and prevents preterm labor.

Thyrotropin-releasing hormones: potential anti-depressive; works by stimulating the release of thyroid-stimulating hormone, which in turn triggers hormone production in the mood-mediating thyroid gland. In pill form, it’s used to treat PMS and depression.

Serotonin: increases sperm motility.  It also mediates mood, although not much known yet about vaginal absorption. Even if it doesn’t make it to the brain, it may indirectly alter behavior and emotions by contributing the building blocks of serotonin

Melatonin: increases effects of steroid hormones; induces sleepiness and fatigue, which may help the woman relax after sex; may stimulate reproductive function, also mood mediator; low melatonin levels are associated with depression and “reality disturbance”

Tyrosine: a precursor of neurotransmitters such as dopamine, the hormone of reward and addiction, and norepinephrine, involved in attention and arousal

Oh, and there’s also sperm in there, the DNA-bearing courier. Sperm is less than 3 percent the total volume of semen. But as it turns out, the bath water is nearly as important as the baby.

n.b. Although not yet studied, researchers suspect that these chemicals in semen may also enter the bloodstream through mucous membranes when having oral and anal sex. If so, straight women aren’t the only lucky recipients.

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