Twin

For Females, Twinning is Not Winning: Research Suggests Girl Twins Disadvantaged by Testosterone

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While twinning may not equal winning for some fraternal girl twins, the upsides to being a twin remain. (Patryk Kosmider/Shutterstock)

While twinning may not equal winning for some fraternal girl twins, the upsides to being a twin remain. (Patryk Kosmider/Shutterstock)

Since the early 1980s the number of twins born in the United States has risen by 60 percent. From the parents’ point of view, that may mean getting two for the price of one (hooray!) or signing on for double trouble (ut oh).

Still, whether twin parents are delighted or terrified, scientific research suggests that moms of twins live longer than moms of singletons. The reasons are not clear—it may be that women who birth twins are healthier to begin with or that having twins, like having children later in life, confers a longer life span. Whatever the reason, it’s nice to know that running around after your dynamic duo may sabotage your sanity but won’t shave years off your life.

But what about from the twins’ point of view?

While it may be wonderful to have a constant companion, built-in best friend, and someone to blame for the window you just broke, scientifically speaking there appear to be both advantages and disadvantages to being born a twin.

A Longer Life Span?

Research from a Danish database published in 2016 found that identical twins and fraternal twins both outlived their counterparts who were not twins. Interestingly, this twin longevity advantage was especially true for identical male twins.

For this study, scientists from the University of Washington in Seattle found that identical twins had a survival advantage over fraternal twins. But being a twin of any ilk resulted in several extra years of life.

The scientists examined data on nearly 3,000 same-gender twin pairs who were born at the turn of the 20th century (between 1870 and 1900).

The scientists found that the twins’ average life spans were up to five years longer than the average in Denmark at that time.

The researchers called this observed increased longevity a “twin protective effect.”

While the reasons twins may live longer than their non-twin counterparts are not entirely clear, scientists have speculated that it may be because of the strong social bonds between twins.

Having a sibling the same age, for instance, might keep you from engaging in risky behaviors, while also providing you with emotional, practical, and even financial support.

This 2016 study was limited by the small sample size and the fact that the twins were born over a hundred years ago in a country with midwife-led birthing practices. In addition, at the turn of the century, the vast majority of twins were born vaginally in every country in the world.

The Bane of Abdominal Birth

Since the mid to late 1960s, however, more American twins started to be delivered abdominally. Between 1995 and 2008 cesarean delivery rates for twins increased dramatically, from 53 percent to 75 percent, according to a 2011 analysis published in the journal Obstetrics and Gynecology.

This is bad news for babies, as hundreds of scientific studies now link cesarean birth to poor health outcomes later in life.

For example, a 2015 article published in the British Medical Journal found that children delivered via C-section have higher incidences of type 1 juvenile diabetes, obesity, and asthma. All of these conditions are associated with decreased quality of life and shorter life spans.

Lower Life Outcomes

Besides the complications that come from cesarean birth, there may be another health disadvantage to being a twin—for a girl twin sharing her mother’s womb with a brother anyway.

Consider this: a 2019 study published in the journal the Proceedings of the National Academy of Sciences found that female twins who are exposed to male hormones in the womb suffer negative impacts later in life.

The study found that baby girls who are exposed in utero to a male twin may not fare as well when it comes to education, salary, and fertility.

This was a large longitudinal study. The scientists examined the outcomes of more than 13,700 Norwegian twins born between 1967 and 1978. They found that females exposed to higher levels of male hormones in the womb due to being conceived with a male twin had what they called lower life outcomes than female twins who gestated with another female twin.

Indeed, girls who gestated with boys had a lower likelihood of graduating from high school or university. They also had fewer children, and earned less money as young adults than girls who gestated with girls.

A Pre- or Post-Natal Problem?

The study’s lead author, Dr. Krzysztof Karbownik, earned his Ph.D. in economics at Uppsala University in Sweden and is currently an assistant professor of economics at Emory University in Atlanta, Georgia.

After finding this negative impact on girl twins who gestated with boys, Karbownik and his team of scientists wanted to determine whether the differences seen in the female twins’ life outcomes were due to growing up with a brother of the same age—or if they were the result of something that happened in utero.

To answer this question, the researchers studied another group of twins. These were girls who were separated and raised apart from their male twin brothers.

Hormonally Charged: The Twin Testosterone-Transfer Hypothesis

It turned out that the negative effects on life outcomes were still present for girl twins, even when the girls were not raised with their twin brothers.

This suggests that the differences seen in the female twins’ life outcomes were the result of what is called the “twin testosterone transfer hypothesis.”

This hypothesis posits that male hormones are transferred from the male twin to the female twin during pregnancy.

While the data is mixed, animal studies have also found that females that share a litter with males differ from females born in all-female litters. This supports the idea that exposure to male hormones in utero can have subtle but potentially deleterious effects on female twin development.

The 2019 study was the first of its kind to track twins for more than 30 years, following them from birth to adulthood. Though the differences in outcomes were not large, they were statistically significant, according to the researchers.

Other previous studies have also found a potential negative effect for twin girls who shared a womb with a brother.

For example, a 2007 study using the health records of Finland found that girls with twin brothers were 25 percent less likely to have children and 15 percent less likely to marry if their twin was male. This team of British and Finnish researchers suspected that what they called “hormonal interactions,” that is, exposure in the womb to testosterone, damaged the female twins’ fertility.

Seeing Double

These days something like 1.6 million twins are born each year, which means one in every 42 babies born is a twin, according to WebMD.

In one southwestern city in Nigeria, West Africa, nearly every family has twins or even triplets.

In fact, there are so many twins in Igbo-Ora that the city hosts an annual festival to celebrate them.

At this year’s celebration, over a thousand pairs of twins were in attendance, according to NPR. No one is sure, but locals think the reason for the high numbers of twins may be partly because women’s diets are high in amala, a dish made from white yams, which are a staple among the Yoruba in Nigeria.

Worldwide, the number of twins appears to be increasing due to more couples using in vitro fertilization and other assisted reproductive technologies.

Should these families with twins and expectant couples be concerned? Probably not.

While twinning may not equal winning for some fraternal girl twins, the upsides to being a twin remain. Besides, females who gestate with boy twins may have advantages in other aspects of their lives that were not measured by the 2019 study. As the scientists explained, “it may be that females gestating with male co-twins excel in other domains of life that we are unable to measure in our data.” In addition, they concluded, changing social norms and cultural mores may also turn some perceived disadvantages into advantages over time.

Could You Have Look-Alike ‘Twin’ Who Might Even Share Your DNA?

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Most everyone has played the “separated-at-birth” game, joking that look-alike friends and even celebrities who aren’t related might have a secret shared parentage.

But new research shows it’s no joke that, with some doppelgangers, there is in fact more to the idea than meets the eye. A team of Spanish scientists studied pairs of unrelated look-alikes and found that they not only bear a striking resemblance to each other, but also share significant parts of their DNA.

The findings, published in the journal Cell Reports, suggest those genetic similarities might extend beyond just facial appearance. DNA analysis based on the new work could one day help doctors identify a person’s hidden risks for certain diseases and even help law enforcement officials target criminals through biometric forensics, the researchers say.

But perhaps the most fascinating takeaway is the likelihood that most people on the planet have an unrelated “twin” out there somewhere, says Manel Esteller, PhD, a researcher at the Josep Carreras Leukemia Research Institute in Barcelona, who led the study.

“It’s not unreasonable to assume that you, too, might have a look-alike out there,” he says.

Esteller’s new study grew out of his research into the similarities and differences among identical twins. He was inspired by a photography project by French-Canadian artist François Brunelle, who has been taking pictures of unrelated look-alikes worldwide since 1999. His remarkable photographs prompted Esteller to ask: Could DNA explain these look-alike “twins”?

“In 2005 we discovered that brother twins that have the same DNA [also called monozygotic twins] presented epigenetic differences [chemical changes in DNA that regulate how genes are expressed] that explained why there were not perfectly identical,” he explains.

“In the current study, we have explored the other side of the coin: people that have the same face, but they are not family related. These individuals helped answer the longstanding question of how our aspect is determined by nature and/or nurture.”

To answer that question, Esteller’s team recruited 32 pairs of people from Brunelle’s photo sessions to take DNA tests and complete lifestyle questionnaires. The researchers also used facial recognition software to assess their facial similarities from headshots.

They found that 16 of the look-alike pairs had scores on par with those of true identical twins, who were also analyzed by the team’s facial recognition software. Of the look-alike pairs, 13 were of European ancestry, one Hispanic, one East Asian, and one Central-South Asian.

The researchers then examined the DNA of those 16 pairs of look-alikes and found they shared significantly more of their genetic material than the other 16 pairs that the software deemed less similar in appearance – a finding the researchers said was “striking.”

Esteller notes that it would seem to be “common sense” that people who look alike should share “important parts of the genome, or the DNA sequence,” but that had never been scientifically shown – until now, that is.

“We found that the genetic sites shared by the look-alike corresponded to four categories,” he says. “Genes previously reported to be associated with the shape and form of the eyes, lips, mouth, nostril, and other face parts using general population studies; genes involved in bone formation that can relate to the skull shape; genes involved in distinct skin textures; [and] genes involved in liquid retention that can give different volumes to our face.”

While the doppelgangers’ DNA was closely matched, Esteller was surprised to find that the lifestyle surveys – assessing 68 variables – revealed major differences in the 16 pairs of people. These differences were almost certainly due to the environment and other parts of their lives and upbringing (think: “nurture vs. nature”) that didn’t have anything to do with their genetic makeup.

Those differences, he explains, are another sign the similarities in the pairs’ appearances almost certainly have more to do with their shared DNA than other things.

Even so, he found some look-alikes were alike in ways that could be linked to their DNA – such as height and weight, personality traits (such as nicotine addiction), and even educational status (suggesting intelligence might be linked to genes).

“It is said that our face reflects our soul,” Esteller says. “Being less poetic, our look-alike answered a large questionnaire to grasp their physical and behavioral profiles. We observed that those look-alikes with high concordance in the facial algorithms and genetic commonalties not only shared the face, but also other features. …”

So, what explains those genetic similarities? Esteller says it’s likely that it’s chance and coincidence, spurred by population growth, and not a result of some prior, unknown ancestral or familial link. There are, he explains, only so many things that make up human facial features, so it stands to reason that some people – by luck of the draw – will resemble others.

“Because the human population is now 7.9 billion, these look-alike repetitions are increasingly likely to occur,” he says. “Analysing a larger cohort will provide more of the genetic variants shared by these special individual pairs, and could also be useful in elucidating the contribution of other layers of biological data in determining our faces.”

Beyond the weird-science appeal of the study, Esteller believes his findings could help diagnose diseases, using DNA analysis. They might even help police hunt down criminals one day in the future – giving forensic scientists, for instance, the ability to come up with sketches of suspects’ faces based only on DNA samples found at a crime scene.

“Two areas are now very exciting for further development,” he says. “First: Can we infer from the face features the presence of genetic mutations associated with a high risk of developing a disease such as diabetes or Alzheimer’s? Second: Can we now from the genome be able to reconstruct a face that would be extremely useful in forensic medicine? Both avenues of research can now be pursued.”

Hear It From the Doppelgangers

For Marissa Munzing and Christina Lee, who took part in the look-alike study, the social implications of Esteller’s research are at least as important as the scientific findings.

Marissa Munzing and Christina Lee.

Munzing, who has known Lee since they met freshman year at the University of California, Los Angeles 14 years ago, did not expect to find that their DNA was such a close match.

“I was definitely surprised that [we] might have similar DNA, as close to being twins, with my friend,” she said in an email. “How crazy!! And cool! I do call her my ‘twin’ from time to time so I guess it’s really fitting now!”

But knowing we all might have a secret twin out there could help bring people together at a time when Americans and others throughout the world are so deeply divided along class, social, and political lines, she says.

Lee agrees, noting that having a friend with a closely matched genetic profile “and even a similar face” adds to a sense of connection with others we might consider strangers.

“It can be nice to feel like you aren’t alone, even if is just in your looks,” she says.

“We really are more similar and connected to each other than we think,” Munzing says.

Jealousy: it’s in your genes.

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A tear-filled green eye

Around a third of the variation in levels of jealousy across the population is likely to be genetic in origin. Photograph: Tim Flach/Getty Images

How would you feel if you suspected your partner had enjoyed a one-night stand while away on holiday without you? What if, instead of having sex on the trip, you believed she or he had fallen in love with someone? In either case, if your partner will probably never see the other person again, would that make the situation any easier to cope with?

Faced with either scenario, most of us would feel intensely jealous: it’s a very basic, normal reaction. But does the universality of jealousy indicate that it might be genetically programmed?

The first study to investigate the genetic influence on jealousy was recently published. Researchers put the questions at the top of this article to more than 3,000 pairs of Swedish twins. Fraternal twins share about 50% of their genes; identical twins share exactly the same genetic make-up. By comparing the answers given by each group of twins, the researchers were able to show that around one third of the differences in levels of jealousy across the population are likely to be genetic in origin.

In both scenarios – fears about a partner sleeping with or falling in love with a stranger – women reported more jealousy than men. But the researchers also found a gender difference between relative reactions to the idea of sexual or emotional betrayal. Men were far more troubled by the thought that a partner had been sexually unfaithful than by potential emotional infidelity. Women tended to respond to each scenario with equal levels of jealousy.

Why is this? The answer, according to some scientists, may lie in evolutionary pressures. For both men and women, reproduction is key. But men, unlike women, cannot be certain that they are the biological parent of their child, and so they are naturally more perturbed at the thought of sexual infidelity than they are about emotional infidelity – because it jeopardises the successful transmission of their genes. Women, though relatively less perturbed by the idea that their partner may have been sleeping around, are nevertheless dependent on their mate for their survival and that of their offspring.

That’s the theory. Given that we can’t zip back in a time machine to human prehistory, it’s an explanation that seems impossible to prove or disprove.

Though genes appear to play a part in jealousy, the Swedish results also show that the kinds of things that happen to us in our lives – the way we’re brought up, the people we’re around, the events we experience – are far more important. Only one third of the variation in jealousy seemed to have a genetic origin, so the rest must have been down to environmental differences.

But whether genetic or environmental, hardwired or learned, there’s no doubting the ubiquity of jealousy. It’s an emotion that almost everyone feels at some point, and a major cause of relationship problems. Although much of this jealousy is illusory, we all know that the eye (if nothing else) can wander. In Britain, the National Survey of Sexual Attitudes and Lifestyles found that 82% of men and 76% of women reported more than one lifetime partner, with more than a third of men and almost a fifth of women clocking up 10 or more. Some 31% of men and 21% of women said they had started a new relationship in the previous year, with 15% of men and 9% of women seeing more than one person at the same time.

Occasionally, then, we have grounds to be worried: jealousy alerts us to a looming problem in our relationship. If your partner has been unfaithful in the past, naturally you’ll worry that they might stray again in future. Much of the time, though, jealousy is pointlessly corrosive, making both partners miserable for no good reason. In these cases, how can we get the better of our jealousy? How can the “green-eyed monster” be tamed?

Consider the evidence for your jealousy. What about the evidence that might contradict our fears? What would we tell someone if they came to us with the same worries? Have a chat with a trusted friend to get an independent perspective on how likely it is that your partner is deceiving you.

Talk to your partner. When two people hold differing views of what’s acceptable in the relationship – how much time to spend together, how frequently to keep in touch, whether it’s okay to stay in contact with ex-partners and so on – misunderstanding and jealousy are always a risk. If you haven’t agreed the ground rules for your relationship, make it a priority.

Weigh up the pros and cons. People often believe that their jealousy – for all the pain it brings – actually helps them. So it’s a good idea to draw up a list of the pros and cons, both of being jealous and of trusting your partner. On balance, which one seems the best option?

Get to the bottom of your fears. What is it, do you think, that lies at the root of your jealousy? Do you dread being alone? Do you fear humiliation? When you’ve identified the fears fuelling your jealousy, think constructively about how you’d handle the situation.

Set yourself some ground rules. We can find ourselves trapped in a vicious cycle: jealous behaviour feeds jealous thoughts, which in turn trigger more jealous behaviour. And so on. To break this cycle, it helps to set ourselves some ground rules. When you find yourself worrying about your partner’s faithfulness, save those thoughts for a daily “worry period”. Set aside 15 minutes each day, and postpone all your worrying until then.

Concentrate on the good stuff. Jealousy skews our perspective. To counter it, we need to make a deliberate effort to view things more positively. That means focusing on the good parts of our relationship: the things about our partner and our life together that we like, the things that keep us coming back for more. Focus on the positive by doing more positive things together. And remember to have your own interests and activities that boost your self-esteem.

Can science explain why I’m a pessimist?

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_68637051_624_compMany of us categorise ourselves as either optimist or pessimist, but what can science tell us about how we got that way and can we change, asks Michael Mosley.

Debbie and Trudi are identical twins.

They have much in common, except that Trudi is cheerful and optimistic while Debbie is prone to bouts of profound depression.

It is likely that her depression was triggered by a major life event, though the twins have different views as to what that event might have been.

By studying a group of identical twins like Debbie and Trudi, Prof Tim Spector, based at St Thomas’ hospital in London, has been trying to answer fundamental questions about how our personality is formed. Why are some people more positive about life than others?

Spector has been able to identify a handful of genes which are switched on in one twin and not the other.

Twin studies suggest that, when it comes to personality, about half the differences between us are because of genetic factors. But Spector points out that throughout our lives, in response to environmental factors, our genes are constantly being dialled up and down as with a dimmer switch, a process known as epigenetics.

With twins like Trudi and Debbie they have found changes in just five genes in the brain’s hippocampus which they believe have triggered depression in Debbie.

Spector, who describes himself as an optimist, hopes that this research will lead to improved treatments for depression and anxiety.

“We used to say,” he told me, “that we can’t change our genes. We now know there are these mini mechanisms that can switch them on and off. We’re regaining control, if you like, of our genes.”

Even more surprising is research which has identified changes in the activity of genes caused by the presence or absence of maternal love.

  • Michael Mosley presents The Truth about Personality on BBC Two at 21:00 GMT on Wednesday 10 July
  • He explores what science can tell us about optimism and pessimism and whether we can change our outlook

Prof Michael Meaney, from McGill University in Canada, is investigating ways to measure how many glucocorticoid receptors are activated in someone’s brain.

The number of active glucocorticoid receptors is an indicator of that person’s ability to withstand stress. It may also be a measure of how well mothered they were at a young age – reflecting how anxious and stressed their mothers were, and how this impacted on the amount of affection they received in their early years.

I am one of a small handful of people who have done their test and had the results. I haven’t told my mother yet.

I see myself as being more at the pessimistic end of the spectrum but would like to change, so I went to visit psychologist and neuroscientist Prof Elaine Fox at her laboratory at Essex University.

Fox is interested in how our “affective mindset”, the way we view the world, shapes us. As well as using questionnaires she and her team look for specific patterns of brain activity.

They began by measuring the levels of electrical activity on the two sides of my brain with an electroencephalograph. It turns out I have more electrical activity in my right frontal cortex than my left. This, Fox explains, is associated with people who are prone to higher levels of pessimism and anxiety.

Then I did another test, designed to measure my “negative bias”. Still wired up I was asked to press a button whenever I saw dots flashing in a particular pattern behind faces being displayed on a computer screen. I was asked not to focus on the faces, just on the dots.

“Sometimes,” Fox says afterwards, “there was an angry face near the dots, sometimes a happy face. Your response time to the dots was faster when they appeared near the angry face.

10 quotes on optimism and pessimism

  • “A pessimist sees difficulty in every opportunity. An optimist sees the opportunity in every difficulty” – Winston Churchill
  • “The man who is a pessimist before 48 knows too much; if he is an optimist after it, he knows too little” – Mark Twain
  • “The point of living, and of being an optimist, is to be foolish enough to believe that the best is yet to come” – Peter Ustinov
  • “Blessed is he who expects nothing, for he shall never be disappointed” – Alexander Pope
  • “A pessimist is a person who has had to listen to too many optimists” – Don Marquis
  • “An optimist may see a light where there is none, but why must the pessimist always run to blow it out?” – Rene Descartes
  • “The basis of optimism is sheer terror” – Oscar Wilde
  • “No pessimist ever discovered the secret of the stars, or sailed to an uncharted land, or opened a new doorway for the human spirit” – Helen Keller
  • “I’m a pessimist because of intelligence, but an optimist because of will” – Antonio Gramsci
  • “I like pessimists. They’re always the ones who bring lifejackets for the boat” – Lisa Kleypas

Source: Goodreads, Brainyquote, Jimpoz

“The reason you were faster is because your attention had already been drawn to the angry face, even though you may not have been aware of that.”

The tests confirmed I have a fundamentally negative bias. To counter this, Elaine suggested I try a short course of CBM (cognitive bias modification) and mindfulness meditation.

Being a pessimist, constantly on the lookout for things that can go wrong, leads to increased stress and anxiety. And it’s more than just a state of mind. It’s powerfully connected to your health.

In one study, which started in 1975, scientists asked more than a thousand inhabitants of the town of Oxford, Ohio, to fill in a questionnaire about jobs, health, family and attitudes towards growing older.

Decades later Prof Becca Levy of Yale University tracked down what had happened. When Levy went through the death records she found that those who had felt the most optimistic about growing older had lived, on average, around seven and a half years longer than those who were more pessimistic.

It was a striking finding and took into account other possible explanations, such as the fact that people who were more pessimistic may have been influenced by prior sickness or depression.

Similar results emerged from a study of nuns done by Deborah Danner and others at the University of Kentucky. They looked at the diaries of 180 Catholic nuns, written when they had entered their nunneries in the 1930s.

They then rigorously scored these diaries for optimistic or pessimistic outlook. Nuns who live in a closed community are a good group to study because they live in the same environment for most of their lives, eating the same foods and having similar experiences.

When the researchers traced what had happened to the nuns they discovered that those who expressed the most positive emotions about life when they were in their early 20s lived up to 10 years longer than those who expressed the least.

As for me, after seven weeks of doing mindfulness meditation and CBM I felt much calmer and returned to Prof Fox’s lab for more tests. The results were extremely encouraging.

It seems that even later in life you can change your outlook. Even for the pessimists, that should be worth celebrating.

Source: BBC