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?

What your date’s fingerprints reveal

Posted in news, psychology, science, sex by jenapincott on February 6, 2011

Not long ago, people everywhere started to do the “finger game” on a first date. This is not as naughty as it sounds. As I describe in BLONDES, the finger game involves asking your companion for a look at his (or her) right hand. If his ring finger is longer than his index finger it’s a sign of prenatal exposure to high levels of testosterone. People with longer ring (than index) fingers are likelier to be more aggressive, better at sports, and more musically inclined. They may have more sex partners in life.

Now you can take the game to the next level: fingerprints.

Take a close look at the ridges on your companion’s fingers. (Actually, they’re best seen under a magnifying lens or photocopied and enlarged.) Most people have slightly more ridges on the fingers of one hand than the other.

More ridges on the right-hand fingers: This indicates higher levels of prenatal testosterone. He or she might master mental rotation – knowing which one of four abstract figures, revolved in three-dimensional mindspace, matches a diagram (a “masculine” task). Right-ridge dominant people are also better at aiming at a target and getting a bull’s eye.

More ridges on the left-hand fingers:
This indicates lower levels of prenatal exposure. He or she may be a whiz at games like word associations, taking a word like clear and coming up with glass then Philip then opera then ghost, or naming as many round objects as she can in three minutes (considered “feminine” tasks). Compared to straight men, gay men have more ridges on their left pinkies and thumbs.

Four or more ridges on the fingers of one hand than the other: This reflects how much stress your companion weathered when he or she was a second-trimester fetus. For instance, researchers found that women who were 14-22 weeks pregnant when an epic ice storm hit Canada were more likely to have babies whose ridge counts varied greatly between hands. In nature, dramatic asymmetry is often a sign that the fetus has been stressed in some way. The more stress, the less symmetry. In fact, those with significantly asymmetric ridge counts between right and left hands were more likely to score lower in language and intellectual development as toddlers. Both fingerprint development and the brain may have been affected by constriction of blood flow to the placenta or stress hormone levels.

Other ridge count studies have also found interesting correlations: a significant difference between the ring and pinky fingers of the right hand is associated with less muscle mass in the lower extremities and a bulked-up upper body, including a thicker waist. A difference of around three or four more ridges between the thumb and pinky fingers is also associated with diabetes later in life. Asymmetries are also connected to cleft lip, dyslexia, schizophrenia, infections, and other prenatal problems.

Around ten weeks after conception is when the bottom (basal) layer of fetal skin outgrows the top (epidermis), and the tension between the two causes the skin to buckle. At this time fingerprints are like wet cement: any disturbance until mid- pregnancy may leave a lifelong impression. At this time the skin and the brain are both are made of the same raw material — fetal ectodermal tissue. Any disruptive event in the womb left its mark on both. This means that fingerprints give us clues about the brain.

You would like to know more about the minds of the people you date, which is why you’re analyzing their fingers. Of course if you could read their minds, you’d know they think you’re crazy.

Do you carry DNA of former lovers in your body?

Posted in pregnancy, psychology, science, sex by jenapincott on January 28, 2011

This bit of science arcanum is especially cringe-worthy.

Many years ago, scientists first discovered that a large minority of women have Y-chromosome gene sequences in their blood. At first glance, this seems strange. Men are born with Y-chromosomes but most women are not. The male cells in these women must’ve come from somewhere else.

But where?

The most obvious source is a fetus. Nearly every woman who has ever been pregnant or had a baby has cells from her fetus circulating in her bloodstream. These cells filter through the placenta and reside in the mother’s bloodstream and/or organs — including her heart and brain — for the rest of her life. This condition is called microchimerism, named after the Greek chimera, a creature composed of the parts of multiple animals. Pregnancy-related microchimerism explains why women with sons would have Y-chromosome sequences in their blood.

This is fascinating enough. But how do you explain why women without sons also have male cells circulating in their bloodstream?

This was the subject of a study by immunologists at the Fred Hutchinson Cancer Center. They took blood samples from 120 women without sons and found that 21 percent of them had male DNA. Women were then categorized into four groups according to pregnancy history: women with daughters only, spontaneous abortions, induced abortions, and no children/no abortions.

While the number of women bearing male DNA was highest in the groups that had abortions (nearly 80 percent), women who had only girls or no babies (20 percent) also had male cells in their blood. For no apparent reason.

There are other reasons why women in the fourth group carried male cells: inherited in the womb from a male twin that passed, from a miscarriage they did not know about, from their mother via an older brother…

Or through sexual intercourse.

There remains a possibility, however remote, that cells from a lover may pass be transmitted during sex. Those cells may hang out forever in the recipient’s body, taking residence in any organ. These cells are the imprint of lovers past, a trace of living history.

Might a woman’s bodily fluids enter a cut in a man’s genitals as well? Could men carry around the genes of women they’ve slept with?

The imagination is stirred. What are those foreign cells doing in hearts and minds? Are they wreaking havoc in our heads? Do the cells of former lovers clash? In a science fiction scenario a person could even take a drop of her own blood, isolate a cell from her former boyfriend, and clone him. Then do with him what she will.

The upshot of this research? It’s yet another reason to use a condom.

Are first-borns really the brightest?

Posted in psychology, science by jenapincott on January 20, 2011

For decades, researchers have observed that, on average, first-borns score higher on intelligence tests than their later-born siblings. This is nothing I’d brag about. I think it inspires resentment and eye-rolling among later-borns. But what many (not all) studies have found is that the further down a child is in birth order rank, the lower his or her IQ compared to older siblings. (Of course, intelligence tests and what they really measure are a controversial bugaboo in and of themselves, but let’s put that aside for now.) There’s no obvious reason for this because siblings often have the same parents and grow up in the same family environment.

The largest study on birth order and intelligence comes from Norway, where psychologist Petter Kristensen and Tor Bjerkedel studied data from a vast sample of more than 240,000 brothers conscripted by the military. Eldest children, it turned out, had an IQ nearly three points higher on average than the second-born siblings and about four points higher than third-borns, after controlling for parental education, marital status, income, mother’s age, and birth weight. (The effect of birth order on IQ does not differ for boys and girls.) A three-point difference in IQ doesn’t sound very significant from a personal perspective, but it is in the big picture. All else being equal, three points can translate into a thirty-point difference in SAT scores. That may make all the difference between admittance into an elite college or a second-tier one, for instance.

The IQ boost was strong when Kristensen compared scores between families (my first-born versus everyone else’s first-born, and my second-born versus all other second-borns and so on) and remained strong in a later study when he compared the scores of kids within families (my first-born versus my second-born versus my third-born and so on). This doesn’t mean that every first-born in every family was brighter. Many later-borns scored higher on IQ tests than their older sib. We’re talking about huge populations here, not individuals.

Even so, you’d think there is something special about the wombs of first-time mothers. It’s like a biological birthright, the first-born as know-it-all. They’re preachy and self-righteous. But they can be useful, too. They show the younger kids how to wheedle ice cream from an addled parent and properly glitter and glue. They know how to make killer snowballs, open a lemonade stand, and coax the dog to stand on its hind legs. They know what people do when they have sex.

t turns out that all this teaching and preaching that is key to Kristensen’s explanation of why first-borns score better on tests. Whether sanctimonious and bossy or generous and caring, the interaction between older and younger sibs helps the elder. They learn by telling. In tutoring others, we all make sense of the world, and this in turn affects how well we do on intelligence tests. “Smarter” comes from being the explainer. In Kristensen’s view, this explanation beats the other big three theories that involve family dynamics — first-borns get more parental attention and are exposed to a more intellectual environment longer; parents have higher expectations of them; and they’re more achievement-oriented. It beats them for one major reason that Kristensen discovered when he dug deeper.

The IQs of second-borns are higher in families in which the first-born has died.

Not only did the second-born rise in family rank when a first-born died, but also in IQ, topping the scores of any younger sibs. Third-borns moved into second-place IQ rank in their families (one point higher) in the few cases in which second-borns in a family died.

There are serious critics of the first-born-the-explainer explanation for higher IQs — especially those who insist there must be a biological reason why first-borns score higher. Although family dynamic can still play a role, there may be another sly and subtle culprit: the physical toll the first-born takes on the mother, and how quickly she recovers from it. Some studies have found that second-borns, especially those with older brothers, have lower birthweights. Significantly lower birth weights, in turn, may affect IQs if there are not enough maternal resources for the new baby. (It didn’t in the Norwegian study, but perhaps the data should be looked at more closely.) A deficit of omega-3s may be also to blame, according to one provocative theory. If Mom used up her store of these butt-based-brain-building fats on the previous baby and didn’t have time to replenish them naturally or supplement them in her diet, the next baby might suffer slightly.

But what can we really learn from this? We can imagine that birth order affects a baby throughout life, and performance on IQ tests is only a sliver of it. For those who buy into birth order psychology, even choice of career can be explained by one’s ranking in the family, which some studies confirm and others do not.

First-borns are said to be more conscientious, conservative, performance-and-power-oriented, disciplined, fearful of losing face, and generally more anxious. This helps explain why more first-borns are presidents, Nobel Laureates, and CEOs.

Every rank has its niche. Middle children are born to rebel. They are less conscientious, less religious, and don’t do as well in school. They’re more sociable, impulsive, and open to fantasy. They’re good negotiators. The babies of the family show more interest in others and are more empathetic. They’re more creative, flexible, risk-taking, impulsive and more extroverted, perhaps because they arrive into a larger, more stimulating household and must compete for attention. Children without siblings are similar to first-borns in that they tend to be ambitious and performance-oriented, but they are often lonely, independent individualists, or, depending on their situation, rely more on family. Kids who grew up with same-sex siblings have been found to be more conscientious and extroverted. Women who grew up with both a brother and sister tend to be more creative, while men tend to be more agreeable.

But is there anything about being a first-born or later-born that affects success and happiness in life? This is ultimately what matters most for our kids — and the answer is that birth order has no impact here. The planet needs explainers and extroverts, contemplatives and can-do types, rebels and realists, visionaries and ancillaries. What one achieves in the world, beyond birth order and standardized exams, is the real test.

Do more babies come out on a full moon?

Posted in news, pregnancy, science by jenapincott on January 12, 2011

Nature still has a subconscious sway over us, and labor brings out the inner animal. We know that circadian rhythms of night and day affect hormone levels, which in turn may trigger contractions. So it doesn’t surprise me when I hear midwives, nurses, and even doctors insist that more births occur on a full moon.

Their logic seems grounded: a full moon has a gravitational pull on amniotic fluid, just as it has on any other body of water. The pressure causes the sac to break, thereby triggering labor.

I’m not the only one who wanted to put this theory to the test. There are over a dozen studies published on labor and la lune (including here and here), totaling hundreds of thousands of spontaneous, non-induced births and hundreds of lunar cycles.

Alas, none have found any significant differences in the frequency of births, route of delivery, preterm delivery dates, or birth complications across the eight phases of the moon (or, for that matter, the weather). It’s a myth, albeit one that has only waxed and never waned – perhaps superstition causes us to see patterns where there are none.

I also found studies that show that contrary to common belief, psychiatric wards are not any busier during full moons than maternity wards. The moon doesn’t make us loonier or more likely to deliver. We do both all on our own.

Why Your Brain Is Better in Love

Posted in media by jenapincott on January 8, 2011

A re-post of my interview with David DiSalvo on his fascinating Neuronarrative column at Psychology Today.

あなたがその人を捕まえたいと思ったら?

Posted in news by jenapincott on November 22, 2010

BLONDES — now in Japanese!

Would you eat your baby’s placenta?

Posted in news, polls, Polls and Surveys, pregnancy, science by jenapincott on November 14, 2010

“You’ve never seen a mother cat with postpartum depression, right?” a woman in my prenatal yoga class asked me. She had a challenging look in her eyes. Before I could respond she rushed to her punchline. “It’s because cats eat their placentas.”

The woman introduced herself as a doula-in-training who prepares placenta on the side. She thought I might be interested.

I learned that placentophagy, the act of eating the afterbirth, is common among other mammals. Animals probably eat it for the extra iron and other nutrients, to detract predators, or possibly to alleviate pain (not to thwart the kitty blues). My fellow yogi is among the small but passionate population of birthing specialists who believe that women should eat their placentas, too — especially to ward off postpartum depression. The placenta is rich in hormones: progesterone, estrogen, cortisol, and others. These hormones originate in the placenta, which means a woman’s levels take a plunge immediately after she gives birth. One theory of why women get depressed after birth is their hormone levels are low. Eating the placenta, it seems, could raise hormone levels enough to ward off depression.

I once bought a placental cream in New Zealand, and the hormones in it made my face break out in violent pustules. That doesn’t make me want to eat the stuff.

“It’s spongy like liver,” the woman said, going for the hard sell. She could use it in lieu of meat in any dish: a simple sauté, lasagna, meatloaf, anything. “Placenta” means “cake” in Latin because it’s round and flat; she could make it into a burger. If none of this appeals, she could have it freeze-dried, emulsified, and made into capsules.

“Oh, but I’m vegetarian,” I said, moving my eyes reverently in the direction of a Krishna wall hanging. But the doula-in-training was armed with a response. “Placenta,” she said, “isn’t meat that is killed.” She patted me reassuringly. “It’s OK!”

“I’m OK,” I automatically responded, as if already stuffed and passing on seconds. I didn’t want to burst her bubble, but sautéing, stir-frying, or even baking placenta would likely change the molecular structure of the hormones in it. I suspect she’d have difficulty attracting clients if they had to eat their bloody organ raw, sushi-style.

As it turned out, my obstetrician had a difficult time removing my placenta. Once out, I let my eyes linger on the silver platter it was heaped on. Weighing in at about a pound and a half, this grayish bloody sack fed and protected my daughter and manipulated me for the nearly ten months of pregnancy. It removed her waste. “It’s got to be tough,” I thought.

But regret came over me as I watched it leave the room. Should I have kept it, tried it? I reminded myself there is no proof that consumption of the placenta wards off serious depression or even the baby blues. Humans in traditional cultures only very rarely eat the afterbirth. Hippies ate it but chimps won’t. Many ethnic groups, honoring the placenta’s indispensability, bury it ceremoniously.

I admit a medical incinerator is not a respectful end. But neither is a vegetarian’s hostile gut. I hate to be close-minded, but my jaws are locked shut.

[Click here for an account of a woman who ate the placenta in the pic above.]

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Mají páni radši blondýnky?

Posted in media by jenapincott on November 12, 2010

Now in Czech by Jena Pincottová!

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