Merging Is Emerging


Til Death Do Us Part

There are very few human beings who receive the truth, complete and staggering, by instant illumination.
Most of them acquire it fragment by fragment, on a small scale, by successive developments, cellularly, like a labourious mosaic.

- Anais Nin

by Helen Pearson

Some people's blood contains cells from a sibling.  Others are two individuals rolled into one.  Yet more carry a distinct mutation in only parts of their bodies.

Eight years ago in Britain, a boy was born who, genetically, was two people.  He was formed when two eggs, fertilised by two different sperm, fused into one embryo inside his mother's womb.  He was an unremarkable baby.  But as a toddler, doctors discovered that he was a hermaphrodite - what was originally diagnosed as an undescended testis turned out to be an ovary, a fallopian tube and part of a uterus.  Further investigation revealed that some parts of his body were genetically female but the rest, which contained a different combination of his parents' genes, was male1.

The boy, who was otherwise healthy, is one of only a handful of known true human chimæras - people carrying tissues that originated in two separate embryos.  More common are mosaics, who have patches of tissue that differ genetically from the rest of their body, thanks to a mutation or chromosomal anomaly that arose early in embryological development.

The frequencies of chimærism and mosaicism are unknown, but doctors might benefit from a better understanding of both conditions.  In recent years, tantalising hints have emerged that pockets of genetically mismatched cells may contribute to conditions as common as infertility, autism and Alzheimer's disease.  "I think mosaicism has been neglected as an underlying cause of disease," says Huntington Potter, who works on the genetics of Alzheimer's at the University of South Florida in Tampa.

And if chimæras and mosaics are more common than we realise, they will complicate future efforts to tailor drug treatments to people's individual genetic constitutions.  Two genetically different tissues in one body might produce an unpredictable response to a drug, speculates Roland Wolf, who studies pharmacogenetics at the University of Dundee, UK.  "It's completely unknown."

Human chimærism first came to light with the advent of blood typing - some people, it emerged, have more than one blood group.  Most are "blood chimæras", non-identical twins who shared a blood supply in the womb.  Those who were not born a twin are thought to be pumping around the remnants of a sibling that died early in gestation and was spontaneously aborted.  One British woman, for instance, was unaware that she once had a twin until routine blood tests during her pregnancy in the early 1980s revealed a population of chromosomally male blood cells2.

Twin embryos often share a blood supply in the placenta, allowing blood stem cells to pass from one embryo and settle in the bone marrow of the other, seeding a lasting source of blood.  As a result, as many as 8% of non-identical twin pairs have chimæric blood3.  And given that most multiple conceptions that result in live births involve the loss of one twin early in pregnancy4, there may also be significant numbers of blood chimæras among single births.

Even more people have "microchimærism", carrying smaller numbers of foreign blood cells that may, for instance, have passed between mother and fœtus across the placenta, or persist from a blood transfusion.  Some researchers argue that the presence of foreign white blood cells might help to explain autoimmune diseases, in which the immune system turns on the body's own tissues5.

True chimæras, in which many tissues are affected, are thought to be very rare, and can form when non-identical twin embryos fuse shortly after fertilisation.  "If you've got two embryos there's the chance of two becoming one," says clinical geneticist David Bonthron, who led the team at the University of Edinburgh, UK, that reported on the British hermaphrodite boy.

Chimærism affecting a variety of tissues can also result from other events.  In 1995, for instance, Bonthron described another boy who was partially parthenogenetic: cells from his blood and certain other tissues contained none of his father's chromosomes; instead, they featured a duplicated set of one half of his mother's6.  Although it is not unknown for an egg to start developing without being fertilised, fully parthenogenetic human embryos cannot develop to term.  Bonthron, now at the University of Leeds, UK, believes that the partially parthenogenetic boy owed his unusual genetic constitution to an egg that spontaneously divided into two cells, one of which was fertilised.  The second cell then copied its maternal chromosomes, allowing the resulting chimæra to form a viable embryo.

True chimæras, including both of those identified by Bonthron's team, generally only come to light if they contain male and female cells, when they can cause hermaphroditism or a mismatch between a person's sexual organs and their chromosomal sex as revealed by a blood test.  So might the condition be more common than we realise?  "I'm convinced that on the streets of London and Hamburg there are many undetected chimæras," says Rudolf Happle, a dermatologist at the University of Marburg, Germany, who has long been fascinated by mosaicism and chimærism.

The rise of in vitro fertilisation (IVF) is almost certainly bringing more chimæras into the world.  To improve success rates, two or more embryos are placed in the uterus, which explains why women undergoing IVF have up to 25% more twin pregnancies than usual.  More twins means more chimæras, says Bonthron, who notes that the British hermaphrodite boy was an IVF baby1.

Mosaicism is more common than chimærism and is also better studied.  Human mosaics arise when a mistake during cell division in the early embryo stops the correct number of chromosomes segregating to each cell, or creates a mutation in a single gene.  If this happens in one of the first few cell divisions after fertilisation, a large proportion of cells will inherit the defect.

Patchy diseases, in which only regions of tissue are affected, might be caused by mosaicism.  Another telltale sign of the condition is a characteristic variation in skin pigmentation that causes patterns called Blaschko's lines, including V-shaped streaks on the back that are sometimes only visible under ultraviolet light.

Mosaicism causes these unusual pigmented
patterns called Blaschko's lines.  © R Hepple

But pinning down the specific mutation in a mosaic disease can prove tricky.  Leslie Biesecker of the National Human Genome Research Institute in Bethesda, Maryland, is attempting to identify the gene that is mutated in Proteus syndrome.  This is the disfiguring condition that the Victorian era "Elephant Man", Joseph Merrick, is thought to have suffered from.  The syndrome's symptoms of patchy tissue overgrowth have led researchers to speculate that it is caused by a mosaic mutation.  Biesecker hopes to compare the genes that are active in diseased patches of tissue with those in unaffected areas using DNA microarrays.  But obtaining tissue samples from the 100 or so sufferers of Proteus syndrome worldwide is difficult, and the genetic differences between tissues may be slight.

Other researchers suspect that mosaicism could be involved in more common diseases.  Wendy Robinson of the University of British Columbia in Vancouver, for instance, is intrigued by the observation that the placenta becomes mosaic in about 2% of pregnancies.  Often, these mosaic placentas contain patches of cells that have an extra chromosome - a condition called trisomy.  Because both fœtus and placenta develop from the same cells, Robinson wonders if many fœtuses contain undetected patches of trisomic tissues that persist into adult life.  "People could have little pockets of trisomic cells sitting around inside them that later lead to disease," she suggests.  Intriguingly, her team has found that some women who experience recurrent miscarriage carry trisomic cells7.

Other researchers theorise that a hidden patch of brain cells with an extra copy of chromosome 21 could be what predisposes some people to Alzheimer's disease.  This idea arose from the long-standing observation that people with Down's syndrome, who carry an extra chromosome 21 in all of their cells, develop symptoms of Alzheimer's at an early age.  Recently, two research groups, including the South Florida team led by Potter, have found that many patients with Alzheimer's also have low levels of cells with an extra copy of chromosome 21 cells circulating in their blood8, 9.

Autism is also is being explored for links with mosaicism.  In unpublished research, Susan Folstein of Tufts University School of Medicine in Boston examined autistic children under ultraviolet light and found that as many as 10% of them had pronounced Blaschko's lines.  She suspects that a mosaic patch of brain cells, unable to migrate or communicate with its neighbours, might be what causes some cases of autism.  But until an underlying mutation can be found, the idea remains unproven.

Given the intriguing results that are starting to emerge, researchers who have studied chimærism and mosaicism are keen to spread the word so that more attention is paid to the clinical significance of the conditions.  At present, they say, most doctors and clinical geneticists are simply not looking.


1.  Strain, L; Dean, J C S; Hamilton, M P R and Bonthron, D T - "A True Hermaphrodite Chimera Resulting from Embryo Amalgamation after in vitro Fertilisation", New England Journal of Medicine, 338, 166 - 169, (1998).
2.  Bird, G W - "Another Example of Hæmopoietic (Twin) Chimærism in a Subject Unaware of Being a Twin", Journal of Immunogenetics, 9, 317 - 322, (1982).
3.  van Dijk, B A; Boomsma, D I and de Man, A J M - "Blood Group Chimærism in Human Multiple Births Is Not Rare", American Journal of Medical Genetics, 61, 264 - 268, (1996).
4.  Boklage, C E - "Survival Probability of Human Conceptions from Fertilisation to Term" International Journal of Fertility, 35, 75 - 94, (1990).
5.  Nelson, J L - "Microchimærism: Incidental Byproduct of Pregnancy Or Active Participant in Human Health?", Trends in Molecular Medicine, 8, 109 - 113, (2002).
6.  Strain, L; Warner, J P; Johnston, T and Bonthron, D T in Nature Genetics, 11, 164 - 169, (1995).
7. Sangha, K K; Stephenson, M D; Brown, C J and Robinson, W P - "Extremely Skewed X-Chromosome Inactivation Is Increased in Women with Recurrent Spontaneous Abortion", American Journal of Human Genetics, 65, 913 - 917, (1999).
8.  Migliore, L et al - "Preferential Occurrence of Chromosome 21 Malsegregation in Peripheral Blood Lymphocytes of Alzheimer Disease Patients", Cytogenetics and Cell Genetics, 87, 41 - 46, (1999).
9.  Geller, L N and Potter, H in Neurobiological Diseases, 6, 167 - 179, (1999).

Source: 2 May 2002 © Nature News Service/Macmillan Magazines Limited

-------- Original Message --------
Subject: Request for more information
Date: 27 Nov 2005 05:38:10 -0000

This message was posted via the Feedback form.
Name: Scott

Comments: I would like to know more about mosaiciasm and chimeras - I believe that I might be one or some form of one.  I have a different colour of hair on parts of my body and when I was younger I had a noticeable v line that separated a darker stomach and lighter chest.  It has since disappeared but my chest hair is black on one side and blonde on the other half.  This happens on other places on my body as well.  Feel free to contact me at


Note: The articles on whether or not a brain is really necessary have been moved to their own page further on in this section.

See also:

bulletThink Twice As Hard - A baby with two brains...
bulletIncompatible Mating - Though a few mothers might regard their fœtuses as parasites, natural selection cannot afford to.  So, by a mechanism that is not yet well understood, fœtuses are exempted from the attentions of the maternal immune system.  This exemption appears to carry a price: the immune system that is so gentle with the child often seems to turn on the mother.  As a consequence, women are more vulnerable than men to auto-immune diseases...
bulletFor more on autism, see What Is Autism? (further on in this section) - Researchers have identified structural differences in the brain of people with autism that may explain why they have problems communicating and socialising.  Scientists used computerised imaging techniques to pinpoint differences in the frontal and temporal lobes of the brain.

It is my understanding that molar pregnancies (which are non-viable) are due to an egg being simultaneously fertilised by two different sperm.  Would they qualify as a chimæras?

Clones of Nature

by Jill Niemark

Can genes explain our passions and prejudices, the mates we choose, that mystery we call the self?  New research on twins upsets some of our most cherished notions about how we become who we are - and gives nature and nurture a whole new meaning.

Last April I went down to West 27th Street in Manhattan to sit in the audience of the Maury Povich show, and meet four sets of identical twins who had been separated at birth and adopted into different families.  I wanted to see if the same soul stared out of those matched pairs of eyes, to contemplate the near miracle of DNA - double helix twisting around itself like twin umbilical cords ticking out a perfect code for two copies of a human.  One pair, a Polish nun and a Michigan housewife, had been filmed at the airport by CNN the week before, reunited for the first time in 51 years and weeping in each other's arms, marveling at their instinctive rapport.  Yet how alike were they really, if one spent her days on rescue missions to places like Rwanda, while the other cleaned houses to supplement her husband's income?

Twins are nature's handmade clones, doppelgangers moving in synchrony through circumstances that are often eerily similar, as if they were unwitting dancers choreographed by genes or fate or God, thinking each other's thoughts, wearing each other's clothes, exhibiting the same quirks and odd habits.  They leave us to wonder about our own uniqueness and loneliness, and whether it's possible to inhabit another person's being.  Twins provoke questions about the moment our passions first ignite - for they have been seen on sonogram in the womb, kissing, punching, stroking each other.  They are living fault lines in the ever shifting geography of the nature/nurture debate, and their peculiar puzzle ultimately impacts politics, crime and its punishment, education, and social policy.  It isn't such a short leap from studies of behavioural genetics to books like the infamous The Bell Curve (by Richard Herrnstein and Charles Murray) and a kind of sotto-voce eugenics.  And so everything from homosexuality to IQ, religious affiliation, alcoholism, temperament, mania, depression, height, weight, mortality, and schizophrenia has been studied in identical and fraternal twins and their relatives.

Yet the answers - which these days seem to confirm biology's power - raise unsettling questions.  Twin research is flawed, provocative, and fascinating, and it topples some of our most cherished notions - the legacies of Freud and Skinner included - such as our beliefs that parenting style makes an irrevocable difference, that we can mold our children, that we are free agents piecing together our destinies.

Today, we've gone twin-mad.  Ninety thousand people gather yearly at the International Twins Day Festival in Twinsburg, Ohio.  We're facing a near epidemic of twins.  One in 50 babies born this year will have a fraternal or identical double; the number of such births rose 33% in 1994 alone, peaking at over 97,000 - largely due to women delaying childbirth (which skewers the odds in favour of twins) and to the fertility industry, which relies on drugs that superovulate would-be mothers.  Recently, a stunning scientific feat enabled an ordinary sheep to give up a few cells and produce a delayed identical twin a - clone named Dolly, who was born with her donor's 6-year-old nucleus in every cell of her body.  The international furor this Scottish lamb engendered has at its heart some of the same wonder and fear that every twin birth evokes.  Twins are a break, a rift in the customary order, and they call into question our own sense of self.  Just how special and unique are we?

The history of twins is rich with stories that seem to reveal them as 2 halves of the same self - twins adopted into different families falling down stairs at the same age, marrying and miscarrying in the same year, identical twins inventing secret languages, "telepathic" twins seemingly connected across thousands of miles, "evil" twins committing arson or murder together, conjoined twins sharing a single body, so that when one coughs the other reflexively raises a hand to cover the first one's mouth.  And yet the lives of twins are full of just as many instances of discordance, differences, disaffection.  Consider the 22-year-old Korean twins, Sunny and Jeen Young Han of San Diego County; Jeen hired two teenagers to murder her sister, hoping to assume her identity.

So what is truly other, what is self?  As the living embodiment of that question, twins are not just the mirrors of each other, they are a mirror for us all.

The woman seated alone onstage at the opening of the Maury Povich show was already famous in the twin literature: Barbara Herbert, a plump 58-year-old with a broad, pretty face and short, silver hair, found her lost twin, Daphne Goodship, 18 years ago.  Both had been adopted as babies into separate British families after their Finnish single mother killed herself.  The concordances in their lives send a shiver up the spine: both women grew up in towns outside of London, left school at 14, fell down stairs at 15 and weakened their ankles, went to work in local government, met their future husbands at age 16 at the Town Hall dance, miscarried in the same month, then gave birth to two boys and a girl.  Both tinted their hair auburn when young, were squeamish about blood and heights, and drank their coffee cold.  When they met, both were wearing cream-colored dresses and brown velvet jackets.  Both had the same crooked little fingers, a habit of pushing up their nose with the palm of their hand - which both had nicknamed "squidging" - and a way of bursting into laughter that soon had people referring to them as the Giggle Twins.  The two have been studied for years now at the University of Minnesota's Center for Twin and Adoption Research, founded by Thomas J Bouchard, Phd.  It is the largest, ongoing study of separated twins in the world, with nearly 100 pairs registered, and they are poked, probed, and prodded by psychologists, psychiatrists, cardiologists, dentists, ophthalmologists, pathologists, and geneticists, testing everything from blood pressure to dental caries.

At the centre, it was discovered that the two women had the same heart murmurs, thyroid problems, and allergies, as well as IQ's a point apart.  The 2 showed remarkably similar personalities on psychological tests.  So do the other sets of twins in the study - in fact, the genetic influence is pervasive across most domains tested.  Another set of twins had been reunited in a hotel room when they were young adults, and as they unpacked found that they used the same brand of shaving lotion (Canoe), hair tonic (Vitalis), and toothpaste (Vademecum).  They both smoked Lucky Strikes, and after they met they returned to their separate cities and mailed each other identical birthday presents.  Other pairs have discovered they like to read magazines from back to front, store rubber bands on their wrists, or enter the ocean backwards and only up to their knees.  Candid photos of every pair of twins in the study show virtually all the identicals posed the same way; while fraternal twins positioned hands and arms differently.

Bouchard - a big, balding, dynamic Midwesterner who can't help but convey his irrepressible passion about this research - recalls the time he reunited a pair of twins in their mid-30s at the Minneapolis airport.  "I was following them down the ramp to baggage claim and they started talking to each other.  One would stop and a nanosecond later the other would start, and when she stopped a nanosecond later the other would start.  They never once interrupted each other.  I said to myself, `This is incredible, I can't carry on a conversation like that with my wife and we've been married for 36 years.  No psychologist would believe this is happening.  When we finally got to baggage claim they turned around and said, `It's like we've known each other all our lives."'

Just Puppets Dancing To Music of the Genes?

I asked Bouchard if the results of his research puncture our myth that we consciously shape who we are.  "You're not a believer in free will, are you?" he laughed, a little too heartily.  "What's free will, some magical process in the brain?"

Yet I am a believer (a mystical bent and fierce independence actually run in my family, as if my genes have remote controlled a beguiling but misbegotten sense of freedom and transcendence).  I was mesmerised and disturbed by the specificity of the twins' concordances.  Dr David Teplica, a Chicago plastic surgeon who for the last 10 years has been photographing more than 100 pairs of twins, has found the same number of crow's feet at the comers of twins' eyes, the same skin cancer developing behind twins' ears in the same year.  Says Teplica, "It's almost beyond comprehension that one egg and one sperm could predict that."

I could imagine, I told Bouchard, that since genes regulate hormones and neurochemicals, and thus impact sexual attraction and behavior, DNA might influence the shaving lotion twins liked or the hue they tinted their hair.  But the same esoteric brand of toothpaste?  Walking into the sea backwards?  This implies an influence so far-reaching it's unnerving.

"Nobody has the vaguest idea how that happens," he admitted, unfazed.  "We're studying a set of triplets now, two identical females and a brother, and all three have Tourette's syndrome.  How can the genes get so specific?  I was talking yesterday in Houston to a bunch of neuroscientists and I said, `This is the kind of thing you guys have to figure out.'  There is tons of stuff to work on here, it's all open territory."  He paused to marvel over the tremendous shift in our understanding of human behaviour.  "When we began studying twins at the university in 1979, there was great debate on the power of genetics.  I remember arguing in one graduate school class that the major psychoses were largely genetic in origin.  Everyone in the classroom just clobbered me.  It was the era of the domination of behaviorism, and although there's nothing wrong with Skinner's work, it had been generalised to explain everything under the sun.  Nothing explains everything.  Even genetics influences us, on the average, about 50%."

Yet that 50% seems omnipresent.  It impacts everything from extroversion to IQ to religious and social attitudes - and drops only in the influence on homosexuality and death.  Though some researchers have criticised Minnesota's twin sample for being too small and perhaps self-selected (how many separated twins out there don't participate or don't even know they're twins?), it generally confirms the results of larger studies of twins reared together - studies that have taken place around the world.  Twin studies allow us to double blind our nature / nurture research in a unique way.  Identical twins share 100% of their genes, while fraternals share 50%.  But usually they grow up together, sharing a similar environment in the womb and the world.  When separated, they give us a clue about the strength of genetic influence in the face of sometimes radically different environments.  Soon Bouchard and his colleagues will study siblings in families that have adopted a twin, thus testing environmental influences when no genes are shared.  Like a prism yielding different bands of light, twin studies are rich and multifaceted.  Here are some of the major findings on nature and nurture thus far:

bulletPolitical and social attitudes, ranging from divorce to the death penalty, were found to have a strong genetic influence in one Australian study.  A Swedish study found genes significantly influenced two of the so-called "big five" personality traits - "openness to experience" and "conscientiousness" - while environment had little impact.  In contrast, environment influenced "agreeableness" more than genes did.  (The two other traits are "neuroticism" and "extroversion.")  Another study, at the University of Texas at Austin, found that personality in identicals correlated 50%, in fraternals about 25%.
bulletBody fat is under genetic influence.  Identical twins reared together will have the same amount of body fat 75% of the time; for those reared apart it's 61%, showing a heavy genetic and mild environmental influence, according to a 1991 study.
bulletBoth optimism and pessimism are heavily influenced by genes, but shared environment influences only optimism, not pessimism, according to a study of 522 pairs of middle-aged identical and fraternal twins.  Thus family life and genes can be equal contributors to an optimistic outlook, which influences both mental and physical health.  But pessimism seems largely controlled by genes.
bulletReligiosity is influenced by genes.  Identical and fraternal twins, raised together and apart, demonstrate that 50% of religiosity (demonstrated by religious conviction and church attendance) can be attributed to genes.
bulletSexual orientation is under genetic influence, though not solely, according to studies by Michael Bailey, Phd, associate professor of psychology at Northwestern University.  In one study he found that if one identical twin is gay, the other is also gay 50% of the time.  However, when Bailey analysed a sample of 5,000 twins from the Australian twin registry, the genetic impact was less.  In identical male twins, if one was gay the likelihood of his twin being gay was 20%; in fraternal twins the likelihood was almost zero.  In women, there was little evidence of heritability for homosexuality.
bulletWhen substance abuse was studied in 295 identical and fraternal twin pairs, year of birth was the most powerful predictor of drug use.  Younger twins were most likely to have abused drugs, reflecting widespread drug use in the culture at large.  Alcoholism, however, has a significant genetic component, according to Andrew Heath, Phd, at the Virginia Institute for Psychiatric and Behavioral Genetics at Virginia Commonwealth University School of Medicine.
bulletAttention deficit disorder may be influenced by genes 70% of the time, according to Dr Lindon Eaves, director of the Virginia Institute for Psychiatric and Behavioral Genetics.  Eaves and colleagues studied 1,400 families of twins and found genetic influence on "all the juvenile behaviour disorders," usually in the range of 30 to 50%.
bulletTwins tend to start dating, to marry, and to start having children at about the same time.  David Lykken, Phd, and Matthew McGue, Phd, at the University of Minnesota, found that if an identical twin had divorced, there was a 45% chance the other had also.  For fraternals, the chance was 30%.  The researchers think this is due to inherited personality traits.
bulletSchizophrenia occurs more often in identical twins, and if one twin suffers from the disorder, the children of the healthy identical sibling are also at greater risk, according to psychiatrist Dr Irving Gottesman of the University of Virginia.  The risk is about twice as high for the children of a twin whose identical counterpart is ill, as it is for the children of a twin whose fraternal counterpart is ill.

Hidden Differences between Twins

A few fascinating kinks in the biology of twin research have recently turned up, weaving an even more complex pattern for us to study and learn from.  It turns out that not all identical twins are truly identical, or share all their genetic traits.  In one tragic instance, one twin was healthy and a gymnast, while the other suffered from severe muscular dystrophy, a genetic disorder, and was dead by age 16.  Yet the twins were identical.

One way twins can differ is in the sex chromosomes that turn them into a male or female, and which contain other genes as well, such as those that code for muscular dystrophy or color blindness.  All girls inherit two X chromosomes, one from each parent, while boys inherit an X and a Y.  Girls automatically shut off one X in every cell - sometimes some of the mother's and some of the father's, in other cases all the mother's or all the father's.  A girl may not shut off her extra set of X chromosomes in the same pattern as her identical twin does.

Identical twins may not be exposed to the same world in the womb, either. It depends on the time their mother's fertilised egg splits - and that timing may explain why some identical twins seem more eerily alike than others.  At Lutheran University, researchers have looked at the placentas of some 10,000 twin births.  They've found that an egg that separates in the first 4 days of pregnancy develops not only into separate twins, but results in separate placentas, chorionic casings, and amniotic sacs.  These twins are like 2 singletons in the womb and have the best chance of survival.  Twins who separate between the 5th and 8th days share a single placenta and chorion, but still have the benefit of two amniotic sacs.  Here, one twin can have a distinct advantage over the other.  The umbilical cord may be positioned centrally on one sac, while the other is on the margin, receiving fewer nutrients.  Studies of these twins show that with a nurturing environment, the weaker twin will catch up in the first few years of life.  However, it's possible that viruses may penetrate separate sacs at different rates or in different ways - perhaps increasing the risk for schizophrenia or other illnesses later in life.

Twins who split between the 8th and 12th days share their amniotic sac, and often their cords get entangled.  One cord may be squeezed until no blood flows through it, and that twin dies.  Finally, twins who split after the 12th day become conjoined - and even though they share organs and limbs, anecdotal evidence suggests that they often have distinctly different temperaments, habits, and food cravings.

In one hotly debated hypothesis, pædiatrician and geneticist Judith Hall, of the University of British Columbia in Vancouver, speculates that twinning occurs because of genetic differences within in an embryo.  Perhaps mutations occur at a very early stage in some cells, which then are sensed as different, and expelled from the embryo.  Those cells may survive and grow into a twin.  Hall suggests this could account for the higher incidence of birth defects among twins.

While identical twins can be more distinct than we imagine, fraternal twins might come from the same egg, according to behavioural geneticist Dr Charles Boklage of the East Carolina University School of Medicine.  Boklage proposes that occasionally an older egg may actually split before it is fertilised by two of the father's sperm.  With advances in gene mapping and blood testing, he says, we may find that one-egg fraternal twins occur as often as do two-egg fraternals.  We may be mistaking some same sex fraternal twins for identical twins.

Twins Who Vanish, Twins Who Merge

Whatever the cause of twinning, once it begins, mysterious and unsettling events can occur.  Some twins disappear or even merge together into one person.  Ultrasound equipment has revealed twin pregnancies that later turn into singletons.  One of the twins is absorbed into the body, absorbed by the other twin, or shed and noticed by the mother only as some extra vaginal bleeding.

Only one in 80 twin conceptions makes it to term as two living people," notes Boklage.  "For every one that results in a twin birth, about 12 make it to term as a sole survivor.  And those people never know they were twins."  Because twins tend to be left-handed more often than singletons, Boklage speculates that many left-handers could be the survivors of a twin pregnancy.  And a few of those twin pregnancies may lead to what Boklage terms a "chimæras," based on the Greek monster with the tail of a serpent, body of a goat, and head of lion - a mosaic of separate beings.  "We find people entirely by accident who have two different blood types or several different versions of a single gene.  Those people look perfectly normal, but I believe they come from two different cell lines."

It's as if fantastical, primitive acts of love, death, merging, and emerging occur from the very moment life ignites, even as the first strands of DNA knit themselves into the human beings we will later become - carrying on those same acts in the world at large, acts that define us, and that we still are not certain we can call our own.

When Twins Die, Kill, Hate, and Burn

Though it doesn't happen often, occasionally in history a set of mythic twins seem to burst into our awareness, more wedded and bonded than any couple, even darkly so.  Some twins live with a passion the rest of us experience only in the almost unbearably intense first flush of romantic love.  England's Gibbons twins are one such pair.  Jennifer and June Gibbons were born 35 years ago, the youngest children of Aubrey Gibbons, a West Indian technician for the British Royal Air Force.  The girls communicated with each other in a self-made dialect and were elective mutes with the rest of the world.  By the time they were 11, they refused to sit in the same room with their parents or siblings.  Their mother delivered their meals on a tray and slipped mail under the door.  They taught themselves to read, and eventually locked themselves in their bedroom, writing literally millions of words in diaries.

Later they lost their virginity to the same boy within a week of each other, triggering jealous rage.  Jennifer tried to strangle June with a cord, and June tried to crown Jennifer in a river.  When publishers rejected their work, they went on a spree of arson and theft, and were committed to Broadmoor, England's most notorious institution for the criminally insane.  "Nobody suffers the way I do," June wrote in her diary.  "This sister of mine, a dark shadow robbing me of sunlight, is my one and only torment."  In another passage, Jennifer described June lying in the bunk bed above her: "Her perception was sharper than steel, it sliced through to my own perception...  I read her mind, I knew all about her mood...  My perception.  Her perception ... clashing, knowing, cunning, sly."

After more than a decade of confinement, they were set free.  That same afternoon, Jennifer was rushed to the hospital with viral myocarditis, an inflammation of the heart, and that night she died.  The pathologist who saw her heart seemed to be speaking poetically of their lethal passion when he described Jennifer's illness as "a fulminating, roaring inflammation with the heart muscle completely destroyed."  June, the survivor, has said that she was "born in captivity, trapped in twinship."  Eventually, June claims, they began to accept that one must die so the other could be free.  Today, June lives in Wales.

Another set of twins, 22-year-old Jeen Young Han (nicknamed Gina) and her sister Sunny, have been dubbed the "evil" and "good" twins by the media, after one tried to murder the other.  Although the twins were both valedictorians at their small country high school in San Diego County and got along well, after they graduated they began to battle one another.  Both sisters were involved in petty crime, but when Gina stole Sunny's BMW and credit cards, Sunny had her jailed.  She escaped, but in November 1996 Sunny and her roommate were attacked and Gina was arrested for conspiracy to commit murder.  She'd planned to have Sunny killed at her Irvine condominium, and then assume her identity.

For twin researcher and obstetrician Dr Louis Keith of Northwestern University Medical School, the idea of killing a twin is practically unthinkable.  "I'm an identical twin, and yesterday I attended the funeral of another identical twin.  I kept trying to imagine what my life would be like without my twin.  My brother and I have had telepathic experiences.  I was in East Germany, being driven on a secluded highway with evening snow falling, and suddenly felt intense heat over the entire front of my body and knew it could only mean one thing, that my brother was sending intense signals to me to call him.  When one of the Communist telephone operators agreed to put the call through, I found out that my aunt had died and my twin wanted me to come to the funeral.  The twin bond is greater than the spousal bond, absolutely."

Raymond Brandt, publisher of Twins World magazine, agrees. "I'm 67, and my identical twin died when we were 20.  I love my wife and sons in a very special way, but my twin was one half of me, he was my first love.  Living without my twin for 47 years has been a hell of an existence."

These remarkable stories seem to indicate an extra dimension to the twin bond, as if they truly shared a common, noncorporeal soul.  What little study has been done on paranormal phenomena and twins, however, indicates that - once again - genes may be responsible.  A study by British parapsychologist Susan Blackmore found that when twins were separated in different rooms and asked to draw whatever came into their minds, they often drew the same things.  When one was asked to draw an object and transmit that to the other twin, who then was asked to draw what she telepathically received, the results were disappointing.  Blackmore concluded that when twins seem to be clairvoyant, it's simply because their thought patterns are so similar.

Is There No Nurture?

Over a century ago, in 1875, British anthropologist Francis Galton first compared a small group of identical and fraternal twins and concluded that "nature prevails enormously over nurture."  Time and research seem to have proved him right.  "It's no accident that we are what we are," contends Nancy Segal, Phd, professor of developmental psychology at California State University at Fullerton and director of the Twin Studies Center there.  "We are born with biological propensities that steer us in one direction or another."

Yet critics of twin studies scoff.  Richard Rose, Phd, professor of psychology and medical genetics at Indiana University in Bloomington, has studied personality in more than 7,000 pairs of identical twins and concluded that environment, both shared and unshared, has nearly twice the influence of genes.

However, both the nature and nurture camps may be looking at the same data and interpreting it differently.  According to Lindon Eaves, unshared environment may actually be "chosen', by the genes, selected because of biological preferences.  Scientists dub this the "nature of nurture."  Genetically influenced personality traits in a child may cause parents to respond in specific ways.  So how can we ever tease out the truth?  Nature and nurture interact in a never-ending Mobius strip that can't be traced hack to a single starting point.  Yet if genes are a powerful and a priori given, they nonetheless have a range of activity that is calibrated in the womb by nutrition and later in life by the world.   "Remember," says Eaves, "only 50% of who you are is influenced by genes.  The other 50% includes the slings and arrows of outrageous fortune, accidents of development, sheer chaos, small and cumulative changes both within and without."

Environment, it turns out, may be most powerful when it limits - through trauma, deprivation, malnutrition.  Studies by Sandra Scarr, Phd, professor of psychology at the University of Virginia, show that IQ scores for white twins at the bottom of the socioeconomic ladder, and for all black twins, are heavily influenced by environment.  Social and economic deprivation keep scores artificially lower than twins' genetic potential.  Otherwise, Scarr postulates, genes bias you in a certain direction, causing you to select what you are already genetically programmed to enjoy.  Children may be tiny gene powerhouses, shaping their parents' behaviour as much as parents shape their children.

"Where does this leave us?" concludes Bouchard.  "Your job as a parent is really to maximise the environment so that you and your children can manifest your full genetic potential."  Under the best of environmental circumstances, our genes might be free to play the entire symphony of self.

And yet what of Irina, the Michigan housewife, and her twin, Yanina, the Polish nun?  I sat with them over lunch, newly united twins who couldn't stop smiling at each other, clasping each other's hand.  Their luminous hazel eyes were virtual replicas, but the two women couldn't have appeared more different otherwise: Irina bejeweled and blonde, Yanina in a combat-green nun's habit, a few tufts of brown hair peeping out, skin weathered.  She described rescuing bloodied children from the arms of mothers who'd been shot to death and rising at dawn in the convent to pray silently for hours; her American counterpart portrayed a life filled with errands, cleaning homes, and caring for family.  "Rushing, rushing, rushing, to get everything done" was Irina's summary of her life.  "Teaching love, the kind of love that will make you happy," was her sister's.  Listening to them speak, one in slow, gentle Midwestern cadences, the other in the rolled drumbeat of a Slavic tongue enriched by laughter and hand gestures, it was hard to believe they carried the same genetic imprint.

To me, their differences are so striking they seem to defy the last 20 years of twin research.  "Right now we understand a little bit about human behaviour and its biological and cultural roots," says Eaves.  "But our lived understanding is far richer than any of that.  People are yielding the ground too easily to genetics."

As I mused over the intricate turnings of twin research, I could only conclude the findings were as complex as the self we hope to illuminate with these studies.  Fascinating, tantalising, yes, but twin research, like any great scientific endeavour, ultimately points us to toward the ineffable, inexplicable.  As Charles Boklage notes: "The development of the self is chaotic, nonlinear, and dynamic.  Very small variations in conditions can lead to huge changes.  Different twin studies give different answers.  And whenever the mind tries to understand something, it has to be bigger than the subject it compasses. You cannot bite your own teeth."

"In the end," says Eaves, "I don't give a damn whether you call it God or natural selection, we're trying to find words that instill reverence for the mysterious stuff from which we are made."  God, fate, genes, luck, a random event like a move to America or Poland, or perhaps something stubbornly individual and free about us all, something that can never be quantified but can only be live... The play of self goes on, and whatever hand or eye has orchestrated us, who in the end, twin or not, can know the dancer from the dance?

My Twin Marriage

A few years ago, I was playing the messages back on my answering machine just as my husband, Jeff, was coming into the apartment.  He heard a familiar voice and ran for the answering machine.  "It's Phil!" he yelled, shrugging out of his coat.  "Pick up the phone.  Phil's calling."  Only it wasn't Phil.  It was Phil's identical twin brother, Jeff.  "Oh, it's me," my husband said sheepishly.  Sheepish in the sense of Dolly, the cloned sheep.

When I was first dating Jeff, the prospect of marrying an identical twin seemed magical.  Jeff spoke of his brother as if he were talking about himself, almost as if he could bi-locate and live two contrasting yet mutually enriching lives.  Jeff worked at a literary agency in Manhattan and loved boy fiction, thrillers, and horror novels, while Phil was overtly spiritual, editing a journal dedicated to the study of myth and tradition.  When they were together they seemed to merge into one complex yet cohesive personality.  They talked like hyper-bright little boys, each of them bringing equal heat and erudition to Stephen King and esoteric teachings, baseball, and the possibility of spiritual transformation.  They argued - and still argue - like Trotsky and Lenin, desperate to define themselves as individuals, yet they define themselves against each other.  Jeff and Phil love their wives and children, but they obey the orders they get from the mothership of their identical DNA.

My husband and his twin brother live by E M Forster's admonition, "Only connect."  The pair e-mail each other at their respective offices 2, 4, even more times a day.  A few weeks ago, Phil wrote Jeff that he was trying to decide his favourite 10 films of all time.  He listed Journey to the Center of the Earth, Star Wars, seven other boy classics, and asked for Jeff's help thinking up a 10th.  "Phil and I decided that Jurassic Park is our favourite movie of all time," announced Jeff the other evening at dinner.  In the course of dozens of soothing little dispatches, Phil's movie list and Jeff's movie list had become one.

My marriage to Jeff has locked me into a triangle.  The bond between these twins amazes and amuses me, yet it fills me with an unappeasable longing.  After all, unlike Phil's wife, Carol, who is an only child, I was conditioned even before I was born to be with a twin.  I am a fraternal twin, a girl born 10 minutes after a boy.  "What do you get out of being a twin?', I asked my husband the first day we had lunch.  "What insight does it give you that's harder for single people to understand?"

"Trust," said my husband.  "That pure physical trust that comes when you know someone loves and accepts you completely because they are just like you are."

I knew the primordial closeness he was talking about.  As tiny premature babies, my brother Steve and I used to cuddle in the same crib holding hands.  My earliest memory is of being lifted up high and feeling incredible joy as I gazed into my mother's vast, radiant face.  I was put back down on a big bed.  I remember sensing another baby lying next to me, my twin.  His presence felt deeply familiar, and I know I had sensed him before we were born.  For me, in the beginning there was the light but there was also the son.  In addition to the vertical relationship I had with Mommy, I also had a lateral relationship, a constant pre-verbal reassurance that I had a peer.  I was in it with somebody else.  This feeling of extending in two directions, horizontal and vertical, made up the cross of my emotional life.

At the age of 3, I remember standing in the grass on a hot, bright day in El Paso, Texas, aware as never before that my brother was different from me, not just because he was smaller then and a boy, but because he was different inside.  I loved him and felt protective towards him, as I would throughout my childhood, but I also felt the first stirrings of rebellion, of wanting to go vertical in my identity, to make it clear to my parents and everybody else that I was not the same as Steve.  I began to relish the idea of not being completely knowable.  I developed a serious underground life.  At 8, I twinned myself with an invisible black panther I called Striker.  At 10, I became a spy I made cryptic notes in a notebook.  I had sinister passport photos taken.  I had a plastic revolver I carried in a plastic attaché case.  You may call me one of the twins, I thought to myself, but I come from a foreign country that has malevolent designs on your own.

No one ever calls me and Steve "the twins" anymore, except as an artifact of childhood.  I tend to think of my birth twin, who is now a Porsche mechanic and a big, outdoorsy guy who lives with his wife and two kids in a small town outside of Boston, as the brother who was with me when I was born, who shared space with me in the womb.  I feel close to him not because we are exactly the same, but because I still have bedrock sensation and empathy for his life.

Jeff claimed that his knowledge of trust from being an identical let him know that I was the person he wanted to marry.  He felt twinship towards me right from the start he said, and I wasn't surprised.  Accustomed to being twins, my husband and I fell right into acting like twins.  We co-authored a book and both edit at Publisher's Weekly, yet we sometimes argue over who gets to use the little study in our apartment as if our identities were at stake.  Lately, I've noticed that when I feel dominated by Jeff I tend to yearn for a "real" twin, a twin who mirrors me so lovingly and acceptingly that I can let go and be myself without fear or explanation.  A single person might escape by daydreaming about a perfect lover, but my fantasies of romantic enmeshment have always incorporated the twin.

Years ago in Manhattan I was invited to attend a ceremony for the Santeria religion's god of thunder, Shango, because Shango loves twins.  On the way, a revered old Cuban santera told me that twins were sacred in Santeria and in the African mother religion of Yoruba because they reflect the intersection of spirit and matter.  Girl and boy twins were especially fascinating, according to the santera.  Most girls were killed by the boy energy, they believed.  A girl had to be very strong to survive.  The moment I heard that I realised that being a twin has heightened the drama of my life.  Human beings are twin double, pulled between the desire to merge with another yet emerge as an authentic self.  Twins fascinate, I believe, because we are an externalised representation of an internal struggle everybody lives with all their lives.  We cast the illusion of solving the unsolvable, though we're no closer than anyone else.

Beyond Nature and Nurture: Twins and Quantum Physics

I've been interested in identical twins ever since I was old enough to realise I am one.  When my brother and I were young we were close but nonetheless epitomised the struggle of twins to achieve individual identities.  Now in our 50s' we have both noticed a real convergence of our intellectual, spiritual and philosophical views.

Are the strikingly similar thoughts and behaviours of twins, even those reared apart, due to nature or nurture - or to a 3rd factor?  What if what I call the "non-local" nature of the mind is involved?  Non-local mind is a term I introduced in 1989 to account for some of the ways consciousness manifests, ways suggesting that it is not completely confined or localised to specific points in space or time.  Nobel physicist Erwin Schrödinger believed that mind by its very nature is singular and one, that consciousness is not confined to separate, individual brains, that it is ultimately a unified field.  David Chalmers, a mathematician and cognitive scientist from the University of California at Santa Cruz, has suggested that consciousness is fundamental in the universe, perhaps on a par with matter and energy, and that it is not derived from, nor reducible to, anything else.  Nobel physicist Brian Josephson, of Cambridge University's Cavendish Laboratory, has proposed that non-local events at the subatomic level - for example, the fact that there are correlations between the spin of subatomic particles, even after they are separated - can be amplified and may emerge in our everyday experience.

In other words, macrocosm reflects microcosm.  Systems theorist Erwin Laszlo has suggested that non-local mind may mediate events such as intercessory prayer, telepathy, precognition, and clairvoyance.  If consciousness is unbounded and unitary, strikingly similar thoughts and behaviours of identical twins' even separated twins, would not be surprising.  Genes do determine how individual brains function, how we each process information, and non-local mind could be easier to access if two brains were almost identical in their functioning.  Indeed, some people see analogies between the behaviour of separated, identical twins and separated' identical subatomic particles.

According to the late Irish physicist John S Bell, if two subatomic particles once in contact are separated to some arbitrary distance, a change in one is correlated with a change in the other - instantly and to the same degree.  There is no travel time for any known form of energy to flow between them.  Yet experiments have shown these changes do occur, instantaneously.  Neither can these non-local effects be blocked or shielded - one of the hallmarks of non-locality.  Perhaps distant twins are mysteriously linked, like distant particles - or, to quote Ecclesiastes, "All things go in pairs, one the counterpart of the other."

Source: Psychology Today July - August, 1997 © 1997 Sussex Publishers

A Singular Pain: When Death Cuts the Bond of Twins

by Neela Banerjee

After her identical twin, Cara, died last year of a drug overdose, life stopped for her, too, Christa Parravani said.  She stopped eating.  Work served as a bitter, inadequate refuge.  For the first time in her life, Ms Parravani, a photographer, was alone.  "I feel guilty for being alive, like it’s a curious and exceptional thing," she said.  Yet when Ms Parravani stood up before a group of strangers at a Midtown Manhattan restaurant last December and told them of losing Cara, she felt a sense of kinship.  They were all people whose twin siblings had died, and they had come together in a bereavement group called Twinless Twins.  One young woman spoke of losing her sister to breast cancer in their early 30s.  Another’s brother died of AIDS.

"There’s this sort of void left when one’s twin dies," Ms Parravani, 29, said of Cara’s death.  "In the claustrophobia of the relationship, there comes a comfort in some way.  It seems unusual to breathe now."

Those who come into the world with another person may not think about the possibility that their twin might die apart from them.  But almost always, one twin dies before another.  From that moment, twins say, the uniqueness of life as a twin carries over into the grief they feel.  People who turn to groups like Twinless Twins by definition had close, though often difficult, relationships with their twin siblings.  Intimacy may be greater between identical twins than fraternal ones, but both kinds of twins said in one study that the loss of their twin hurts longer, and more intensely, than the loss of nearly anyone else.  When their twin dies, the remaining ones often experience profound survivors’ guilt.  They have problems with other intimate relationships.  Birthdays bring on mourning, said Dr Nancy L Segal, professor of psychology at California State University, Fullerton, and director of the Twin Studies Center.

The number of multiple births has risen steadily over the last 40 years, according to the Centers for Disease Control and Prevention, which means the particular grief experienced by twins will spread through the lives of many more.  In 2004, according to the centers, 3.2% of live births were twins, compared with 1.9% in 1984.

Those who aren’t twins seem largely unable to appreciate the depth and complexity of twin bereavement, therapists and twins themselves said.  "Twins need to reach out to twins who have the same experience so that they can end their isolation," said Mary R Morgan, a therapist in New York and an expert in twin bereavement.  "What struck me is that although it takes awhile for any group to trust one another, when twinless twins get together in a group, they seem to sense and trust each other immediately, enabling them to move forward in the healing process."

Research involving twins rarely looks at the relationships between them, Dr Segal said.  Rather, scientists use twins to explore the roles nature and nurture play in a range of health and behavioural phenomena.  Dr Segal, author of Entwined Lives: Twins and What They Tell Us About Human Behavior, studied identical and fraternal twin children at the University of Chicago and found that identical twins tended to cooperate more with each other and were gentler with each other than fraternal twins were.  Her research into bereavement after the loss of a twin, compared with the loss of other relatives, with the exception of children, indicated that identical twins felt a more powerful and persistent grief than fraternal twins, but that both kinds of twins felt that the loss of their sibling was more severe than any other loss.

Twinless Twins was founded in 1986 by Dr Raymond W Brandt, a therapist from Fort Wayne, Indiana, who had lost his identical twin decades earlier.  (Dr Brandt died in 2001.)  The group has 10 chapters around the country and four in Australia, the United Kingdom and Canada.  The group has 400 paid members and 350 registered users of its website.  They hold regional meetings and an annual national convention where people talk about their twins and their loss.  At the national meeting, there are also workshops for spouses and parents of twins.

Telling a roomful of strangers about losing your twin is like going off the high dive, said Michael Caruso, a 58-year-old physical therapist in Highland, Maryland.  In the summer of 1970, a hit-and-run driver killed Mr Caruso’s identical twin, Lee, as he walked a motorcycle with a flat tire down a two-lane road on the Jersey Shore.  Two years before that, Lee had tried to kill himself.  Mr Caruso still cannot distinguish himself from his brother in some childhood pictures.  He was profoundly disturbed by his brother’s suicidal behaviour, and his early death meant they never got to talk about it.  Their family urged him to "suck it up and move on," Mr Caruso said.  He entered romantic relationships looking for a woman to be as close to him as Lee had been, a common reaction to the yearning for intimacy among those who have lost their twins.  After two marriages that failed, therapy and a career helping others in chronic pain, Mr Caruso went to his first Twinless Twins meeting.  Over time, he learned to accept his brother’s loss and that he could not have stopped him from attempting suicide or his eventual death.  He met his current wife, Susan Gray, after starting the meetings, and he says that for the first time, he was not needy in a relationship.  "I let go of the fact that I can’t heal someone," Mr Caruso said.  "I can only offer help."

When Joshua Fleck looks at the grown-ups in Twinless Twins, he sees his own life some day.  He is 11 years old and the only child of Caitlin and Ken Fleck of Horsham, Pennsylvania.  Five years ago, his identical twin, Shayne, died of an inoperable brain tumour.  The boys had the same blue blankets.  After his brother died, Joshua asked that a piece of Shayne’s blanket be stitched into his and a piece from his sewn into his brother’s and placed in his coffin with him.  He still sleeps with that blanket.  A year after his brother’s death, Joshua told his mother that a "big piece of his heart went with Shayne," Ms Fleck said.  She told him about Twinless Twins.  Joshua said he worried about what adults there would think of him, but he found friends at the local chapter and the national meeting.  "When I look at Twinless Twins, they all lost their twins but they’re great people," Joshua said.  "They haven’t gotten over it, because you never really get over it.  But they have lived their lives to the fullest while still remembering their twin."

Carolyn Shane, 56, has finally persuaded her family to take her 9-year-old grandniece to Twinless Twins.  The little girl lost her twin within days of their birth and Ms Shane noticed a reticence and sadness for years.  Ms Shane is the little girl’s special aunt because she lost her twin, too, in different ways, several times.  Ms Shane’s twin brother, Cary Schuman, was born severely brain damaged in their native Illinois.  Ms Shane, who lives in Maplewood, New Jersey, said she always felt a need to protect her brother.  But their parents placed him in an institution when he was 5.  From age 10 - 21, Ms Shane was not taken at all to see her brother.  Her father could not cope with his son’s disability, so Cary was never mentioned at home.  Cary died of cancer 9 years ago.  "I always knew I was an ‘us’, but everyone treated me as a ‘me,’ as just one," Ms Shane said.  Her grief upon her brother’s death was so great, she said, that she felt she was going insane.  That feeling abated once she began meeting with others at Twinless Twins.  "It’s like we have an unbreakable bond of immediate understanding and empathy," she said.

Ms Parravani is now wending her way through the landscape that other twins have traveled.  She and Cara went to college together.  Cara was the writer, she the photographer.  But their shared life was torn apart when Cara was raped, 5 years before her death.  Cara was deeply troubled that her sister could not fully understand what she had been through, Ms Parravani said.  Ms Parravani left graduate school for a time to look after Cara, as Cara’s marriage and her emotional health fell apart.  She could coax her sister outside only to pose for a series of photographs Christa was assembling of twins in different landscapes.  Her sister began to use heroin, Ms Parravani said, and she died of an accidental fentanyl overdose.  "The hardest part is relearning who I am in the world without her," she said, sitting in her gallery in Brooklyn, surrounded by pictures of the two of them.  "Without her, it’s a long road for me."

Source: 1 March 2007 photo credit Christa Parravani/Courtesy of 31GRAND

See also:

bulletTwins in Black and White (in the section on Oddities) - for information on some unusual pairs of twins, including the first known "semi-identical" pair...
bulletReunions Set off Sex Urges (in the section on Relationships) - When meeting their lost relative for the first time the respondents all experienced "an overwhelming and complicated rush of emotions" and an "almost irresistible sense of falling in love."  They all said they had a need to discover an unusual form of closeness and intimacy with their relative, who had felt the same way.
bulletIQ Is Inherited Suggests Twin Study (in the section of Men) - The researchers found that certain regions of the brain were highly heritable.  These included language areas, known as Broca's and Wernicke's areas, and the frontal region, which, among other things, plays a huge role in cognition.

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