Science of Love, Sex, and Babies

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?

Does “stress sweat” make you more compassionate?

Posted in news by jenapincott on August 4, 2009

armpit3Pheromones fascinate me, and not only the ones that mediate sexual attraction.

Several months ago I wrote a post about a study that suggests that airborne chemical signals also mediate stress and fear. Known as alarm pheromones, these chemicals are found in sweat and saliva. In that experiment, sweat from skydivers (collected from pads in their armpits) activated anxiety circuits in the brains of people who sniffed those pads later on. The fascinating theory: Emotions can be communicated by smell. It happens unconsciously.

That was just one study, and naysayers are quick to point out that a solitary experiment doth not prove human pheromones are real. But now there’s further proof.

Researchers at the Universities of Dusseldorf and Kiel in Germany recently published the results of study based on the sweat smells of 49 stressed-out students after a.) taking a final oral exam (stress sweat) and b.) exercising (sport sweat). Sniffing the pads that had been in students’ armpits, volunteers often couldn’t detect an actual odor. Nor could they tell whether they were smelling stress sweat and sport sweat. But it turns out that an area of their brains detected the difference. Only stress sweat — and not sport sweat — triggered brain activity in areas involved in the processing of social emotional stimuli (fusiform gyrus), and empathetic feelings (insula), attention (thalamus).

The implications are fascinating. Is stress contagious? In an emergency situation, it makes sense that we’re “wired” to perceive and respond to the stress of others. An odor that induces attention and anxiety may help a group to focus together or synchronize a fight-or-flight response.

It’s particularly interesting that neural circuits associated with empathy — not just attention — were activated. Are we naturally empathetic creatures? Then again, there’s no proof that the volunteers actually felt more understanding and compassionate when smelling stress sweat even if their brains go through some of the motions. I suspect empathy is context-dependent. Further experiments should look into whether volunteers really are more empathetic (more willing to help a person in distress, for instance) after smelling stress sweat compared to sport sweat. If so, this would be further proof that stress sweat is an alarm pheromone, which, by definition, changes the way we behave after we inhale it.

A thought: Could stress sweat induce compassion in autistic people?

And another thought: If feelings have smells, is happiness also inhalable, communicable?

Are pheromones why the rhythm method doesn’t work?

Posted in news by jenapincott on August 2, 2009

Pregnancy_25_weeks For women not trying to get pregnant, life should be easy. Conception can only happen in the 12-24 hours after ovulation. Sure, sperm may last as many as 3-4 days in the genital tract, hanging around for the egg to arrive. But you’d think not having sex during the 4-5-day window would be sufficient to avoid mishaps. That’s what the rhythm method is — a natural form of birth control that relies on abstinence on fertile days.

But slips happen even among the most careful practitioners of the rhythm method. Some of this may have to do with women not keeping perfect track of their menstrual cycles or having naturally irregular cycles. (I discuss in BLONDES the evolutionary reasons why ovulation is hidden to both women and their partners.) The failure rate for rhythm method is 25 percent each year (with a perfect-use rate of 9 percent).

Why so high?

Another reason could be pheromones. The latest issue of my favorite journal, Medical Hypotheses, includes a submission that suggests that pheromones from men may cause an early ovulation in women. By invoking an early release of the egg — in advance of the expected fertile window — chances of fertilization are higher. As I mention in BLONDES, studies have the found that androstadienone, a testosterone-related compound found in men’s sweat, semen, and saliva, increases the amount of luteinizing hormone in women, which thereby triggering ovulation. It’s possible that high-testosterone men may be likelier to have this effect on their lovers. Their sweat smell alone may do the trick.

As I mentioned in an earlier post, there are other properties in semen that may also trigger early ovulation. For instance, seminal fluid contains follicle stimulating hormone (FSH) and luteinizing hormone (LH), which may coax the ovary to release an egg.

Despite the high failure rate, the Roman Catholic Chruch continues to promote the rhythm method, now renamed natural family planning (adding cervical mucus and temperature data to the regimen). Problem is, we don’t live in a clockwork universe, nor do we have clockwork bodies.

Lose your sense of smell, lose your sex drive?

Posted in news by jenapincott on May 25, 2009

22445 When it comes to human pheromones, there are naysayers. And although there are fewer naysayers now than ever before, they’ve long used one tricky argument to deny the existence of human pheromones. There’s no vomeronasal organ (VNO) in homo sapiens, they say. What good are pheromones without a VNO?

The VNO, a bulb buried deep in the nasal cavity, is rich with neuronal receptors that detect chemical signals from others of the same species. It processes those signals which, in turn, stimulate the hypothalamus which triggers the production of sex hormones. Other animals use their VNOs all the time. When a female pig or dog assumes the butt-up bow-backed mating stance, it’s because her VNO had responded to pheromones from a male. People have vestiges of a VNO, but there’s no evidence that it still works. Many studies suggest our VNOs start to form during fetal development but regress and become non-functional by the time we’re born.

The naysayers say we lost our VNOs when we lost our need for pheromones. We’re not animals, they say. We don’t need to sniff out our mates.

But how do you explain the abundant evidence that we still use pheromones when dating and mating (as I detail in BLONDES)?

It turns out that we may have lost our VNOS, but not our noses. That is, we don’t need a VNO anymore because we process pheromones through our regular olfactory channels. We inhale them just as we inhale any other smell. They hit the brain in the same way they would if we still had a VNO.

There’s fresh proof of this in a new study. Neuroscientist Ivanka Savic and her team at the Karolinska Institute in Sweden recruited volunteers to smell known pheromones ( estrogen-related compounds). The volunteers were unusual in the one thing they had in common: they were all straight men who had lost their sense of smell (amnosia) due to nasal polyps. Their olfactory channels were dysfunctional.

Savic and her colleagues knew from their previous experiments that the areas of the brain involved in mating are activated when people smell pheromones. (Their studies are fascinating; they help answer questions in the book such as “Can you tell people’s sexual orientation by their smell?”) When straight guys smell estrogen-related compounds, researchers normally see the hypothalamus normally light up on a fMRI scan. The hypothalamus triggers the release of sex hormones. But does the hypothalamus get stimulated when people lose their ability to smell?

The answer is no. None of the amnosiac men in Savic’s study could process the estrogenic pheromones the way other straight men do. Their brains showed none of the usual activity. The hypothalamus was silent.

This is important. It suggests that, yes, we do appear to process pheromones through the main olfactory system. It’s good news because it implies that we don’t need a VNO to get a pheromonal punch. But we do need to smell. (An interesting study would compare the sex lives of amnosiacs with others.)

The bad news is that it’s possible that if you lose your sense of smell…lust may lose its luster.

DIY Pheromones!

Posted in news by jenapincott on March 11, 2009

morty In BLONDES I describe how pheromones such as androstenone and hormones such as oxytocin have been found to influence mood and possibly attraction — but the effects are subtle and context-dependent.

Several readers saw the text box in which I mention the DIY-ers who are concocting their own pheromones (so-called -mones or pheros) in basement labs, or ordering commercial formulas online, and trying them on in social situations such as on the subway or a first date. No shock: most of the dabblers are guys. Some suffer from social anxiety and a gaping suspension of disbelief. (But insatiable curiosity is always an acceptable excuse.) Others are women, sometimes lovelorn girlfriends seeking to jumpstart a sputtering sex life or recapture the magic of the first few months of a love affair. To these idealists, the chemical route to a person’s heart is more compelling than the psychological. If only there were really such a thing as a love potion.

“How do I find these forums?” eager readers have asked. Here are a few links below — some are interesting observations, others analyze sprays and so on. There’s no harm in dabbling with dab-ons, I believe. Make-your-own-mones! Find-your-own-pheros! As long as you don’t take it too seriously.

Many of the pheromones discussed are related to androstenone (male scent) and copulins (female scent) and the hormone oxytocin. Wearers experiment to get the right amount and type of chemical that match their own body chemistry. (The book describes the actual pheromone studies in some detail.) There is real scientific evidence that sweat-derived chemicals have a moderate effect in some situations. But these underground Boyles and Curies have their own approach, totally unburdened by the scientific method:

The Pheromone Information Library

In the confusing world of pheromone retailers telling their customers whatever they want to hear to get them to buy their products, the Pheromone Information Library provides unbiased and accurate information written by existing users of pheromones.

Love-Scent Forum
Discussion of pheromones and other topics related to the science of attraction
A few interesting threads:
The pheromone help list (dosing, technique, experiences, philosophy, etc.)
Sweat the secret to making pheromone sprays work?
Getting an ex-boyfriend back

Advice, tips & tricks for chemical DIY-ers as well as good old-fashioned advice on basic interpersonal relations. Members share their formulaic faves
A few interesting threads:
The Snook’s big book o’ pheros for rookies
[Research] Vagina lovers: Who can best describe the aroma at its most attractive?
What works: Intimacy/Long Term Relationships (& sex, sex/sensual “enhancers”)
Kitty’s Curious Combos (aka MixMistress)

Discusses pheromones along with commercial fragrances

Drugs-forum strives to be a information hub of high standards and a platform where people can freely discuss recreational drugs in a mature manner.

Oxytocin Forum
Oxytocin is the pair bonding hormone that creates a feeling of trust, bonding and love within mammals. This forum explores whether it works as a spray.

Not to detract from the fun, but do take all these anecdotes with a healthy dab o’ doubt. A recent study led by biologist Craig Roberts suggests that, sure, spray-ons work. Women judged men wearing a special male scent as more attractive. Funny enough, they also thought the fragrance-wearing men were more attractive when watching them in a video where they could not be smelled. In still pictures, however, fragrance wearers were no more attractive than men who didn’t wear fragrance. It turns out it’s not the chemical that makes men more attractive. It’s their mien and bearing — the confidence they got from believing it works.
Then again, maybe they hadn’t yet struck that perfect pheromonal chord.

You smell fear, whether you realize it or not

Posted in news by jenapincott on December 29, 2008

_44173138_fearmale1Our bodies speak to one another in airborne chemical signals that bypass our conscious brains. In BLONDES I fixate on this truth, detailing studies that have shown exactly how these chemicals, called sex pheromones, can trigger sexual attraction. Some studies show that sex pheromones have a marked effect on behavior — potentially making women more receptive, upbeat, and attracted (in the case of androstadienone-related odors) and men more drawn to the body odors of a woman when she’s most likely to conceive (in the case of estrogen-related odors).

And now a news flash: sex pheromones aren’t the only types of pheromones that may affect human behavior. There are also alarm pheromones – chemical signals, like fear gas, that make a person more alert, more on edge. Stony Brook University neurobiologist Lilianne Mujica-Parodi and her colleagues taped absorbent pads into the armpits of 144 first-time skydivers, collecting their fear sweat before and during a 13,000-foot free-fall jump. Then the research team enlisted another set of volunteers to smell either a.) the skydivers’ sweaty pads (fear sweat); or b.) pads worn by sweaty subjects who had simply been working out (exercise sweat), while having their brains scanned by fMRI. Although participants rated fear sweat and exercise sweat as having a similar intensity, their brains responded to the two sets of sweats in dramatically different ways. It turned out that fear sweat — and only fear sweat — triggered activity in the left amygdala, the region of the brain associated with fear. When shown pictures of faces with expressions that ranged from happy to furious, and asked to identify the emotion, people exposed to fear sweat were more accurate when distinguishing between angry and neutral expressions. A chemical component of the sweat, it appears, put them on their guard. The researchers call it “second-hand stress.”

None of this is surprising to biologists because other animals, even mammals, use alarm pheromones all the time. After inhaling alarm pheromones, rats and deer sniff and pace around, unable to let down their guard.

I’m intrigued by this. Alarm pheromones are a hidden biological component of our survival as social anim
als. Anywhere people are stressed or scared — exam rooms, hospitals, interrogation chambers, battlefields, trading floors, sports matches — there’s a residue in the air. Call it an ambient emotion. Call it emotional infection. Call it evolutionary hardwiring that primes us to act when there’s danger. Are some of us more sensitive to it than others? Probably. And its effect on behavior is no doubt context-dependent. I’d like to see more studies, a bigger n, and more distinction between genders.

Like many writer types, I’m hyper-sensitive to the emotions of others, sometimes to the detriment of my psychological well-being. If you’re scared, I worry. My guard goes up, too. Block my my olfactory system, the odor processing region where alarm pheromones may be processed — and would I be less sensitive to your stress?

%d bloggers like this: