August 25, 2011

How often do fraternal twins wrongly believe themselves identical?

Here's a good article in Slate's Twins Week by writer Barry Harbaugh about getting a genetic test to see if he and his twin brother Russ, a filmmaker, are identical twins (as they've always believed) or if they might be fraternal. 

The theme of the article is something I wrote about for Taki's Magazine last year: that identical twins are more likely to incorrectly call themselves fraternal than fraternal twins are to incorrectly call themselves identical. What Freud called the narcissism of small differences operates on twins. In 2010, I concluded: "While movie twins look alike but act wildly different, real-life twins often see themselves as less similar, both in looks and personality, than they appear to strangers."

Barry Harbaugh writes:
And yet: We are not strictly identical. We have our petty discordances, which in their accumulation conspire against us. Suspicion is lured by doubt. In a giant senior-class photo of Russell and me that hangs framed in my old bedroom, we might as well be cousins. I am perched at his left shoulder, looking like my head is balancing on a drinking straw, while his own neck threatens to split his collar. We had long ago compared our fingerprints in vain. He was an All-State high-school quarterback (and an All-American in college), while I sat on the bench for a beleaguered basketball team that couldn't win even five games.

Russ was a small college All-American at Wabash. (At first, I guessed that they are related to Jim Harbaugh, a former NFL quarterback now an NFL head coach, whose brother John is also an NFL head coach. But I can't find any proof for that. Still, I wouldn't be surprised if they are all part of an extended family. All these Harbaughs come from the same part of the country -- Indiana, Ohio, Michigan -- and are all motivated and talented.)
Though we've both escaped the primordial sludge of the Ohio River Valley for New York City, no one confuses us anymore. For two years, I've spent $80 a month on a pharmaceutical that will keep me from going bald. We've noticed that I'm slightly taller. That our noses have a slightly different bent. Our penmanship is at odds and his hair is falling out. ... 
We brought this upon ourselves. Russell and I tried very hard to cultivate individual interests and attitudes. Without surveying the various parenting fashions of twins in history, I might point out the school of thought that demands parents dress their identical children in matching outfits, parting their hair on opposite sides (like a mirror's reflection!), and just as well the school filled with parenting books advising the opposite.
However we came to it—whether through a mother's growing devotion to those books, or some innate desire on our part to complement each other—Russell and I have long attached ourselves to different things, and driven each other crazy with a manic desire to report in detail whatever the other missed. 

This tendency to differentiate can be fairly inevitable, especially among very ambitious twins like the Harbaughs, who are the sons of college professors. If you are named Harbaugh, the top position in sports is quarterback, and only one of you can be the starting quarterback, assuming you don't go to different high schools. If you are named, say, Barber, you can go to the NFL as a cornerback and as a running back and be roughly equally successful. But if you are named Harbaugh, well, there's quarterback, and then there's placekicker, punter, tight end, fullback, center, placekick holder, wedge-breaker-upper, waterboy, and various other football jobs that aren't anywhere near as good as being quarterback. So, it makes sense for one identical twin to break the logjam for both of them by saying, "I don't want to be quarterback. Being quarterback is stupid. I don't care about being quarterback. I want to be [something very opposite of being quarterback, like being a writer.]"

That's fairly important to grasp for thinking about twin studies of nature and nurture that compare identical and fraternal twins. Yes, it is true that other people treat identical twins more identically, on average, than fraternal twins. But identical twins have subtle stresses pushing them apart that fraternal twins are less prone to. If one fraternal twin is built like a quarterback, the odds are that the other one isn't. But if one identical twin is built like a quarterback, then the other one is pretty similar. So, they have to generate their own differentiating forces.



All twins were beheld under the same banner: unusual, unexplained, and undifferentiated.
The confusion was bound with our ignorance of knowing exactly what was happening in utero. It wasn't until the latter decades of the 19th century that embryologists figured out the basic twinning process: Either two sperm fertilize two eggs, or one egg splits in two. (An earlier notion held that twins arose from two sperm that fertilized an ovum in separate places; obviously a red herring.) In 1875, the statistician Francis Galton interviewed 100 pairs of same-age, same-sex siblings, along with their close relatives, and concluded, "Twins is a vague expression." Though not quite a zygotic eureka, he found that extreme similarity among twins was just as common as a moderate resemblance, or hardly any resemblance at all. Even through the embryonic fog, it was clear something elemental divided at least the extremely similar from all the rest. By 1911, the usage of fraternal, as it relates to twins, had entered English usage, and the lexicography of mono- and dizygotic followed five years later. 
Galton's work led to the establishment of the twin method, which proved the foundation for investigations into those dubious sciences called behavioral and eugenic. It also corroborated something that would have been apparent to the era's midwives and cowboys: Not every pair of twins comes into the world trailing the same debris. If you're witness to enough twin births—among humans or cattle—you're likely to notice certain differences from one to the next; that some pairs are born with a single placenta, that others have two placentas fused together, and still more spring from the womb with one placenta each. ...

In 2002, we went off to Wabash College together, a fine all-male school devoted to forging "gentlemen" in upstate Indiana, and one that I stomached for a year before transferring home. The decision was unilateral and it stung. So too: a trip I took that summer to Europe, alone. By sheer coincidence, his football team traveled to Vienna in July, to play an exhibition, and Russell got a tattoo on his left shoulder blade from a man he met in a bar, while I watched. An R whose leg has been cleaved in half so that with a bottom curl it also conveys a B, it proved an unreciprocated mark.

I wouldn't be surprised if there were a big difference between the two twins, one that turns up more often than you'd think among identical twins, one that may have motivated their getting a genetic test to see if they really are identical. (Or I might just be reading slightly more into the various self-dramatizing accounts by the Harbaugh twins than is really there.)

Barry Harbaugh did a lot more research on this question than I did, and came to an even stronger conclusion:
Fraternal twins rarely, if ever, think themselves as alike as two peas. Far more often, misdiagnosis occurs when identical twins think themselves unalike—"of a family likeness only." (In other words, fraternal twins don't question their zygosity; it's the identical ones who get confused). You may have heard that Mary Kate and Ashley Olsen—twins so alike that they have shared professional lives since they were 6 months old, most notably by pretending to be each other without any of their millions fans noticing—have long declared themselves fraternal. What can one say other than: Bahooey. 
As I waited for my own results to come through, I contacted every lab I could find that does this sort of commercial twin testing. I wanted to find stories of identical pairs who had thought themselves fraternal, or of twins that had no idea either way. The search turned up one pair of girls who had grown up with a triplet brother, and couldn't believe the identical result they received: "I never did feel like I was looking at a reflection," one of the sisters wrote. "When the truth finally came out my mom was shocked. She was the mother, how could she get it wrong?" 
But when I asked for help finding a pair that had thought themselves identical, only to discover otherwise—and I shook the bushes for two weeks, badgering labs all over the country—I was met each and every time with silence. Affiliated Genetics, which has been testing for zygosity since 1994, didn't have a single adult twin on record who received a heterozygous result. Not one pair (remotely around my age) had ever tested as fraternal. It seemed nothing short of astonishing. Not one? Where are all the dizygotic wannabes, vainly dressing in matching overalls?

More broadly, something I've discovered over the years that applies to more than just twins is that people seldom appreciate having you point out to them that they look like some famous person. (Sure, 18-year-old girls like to be compared to 21-year-old Victoria's Secret models, but that's about as far as it goes.)

Maybe somebody could put up with being told he looks like the great quarterback Tom Brady, but if you told a guy who looks like the great quarterback Peyton Manning that he looks kind of like Peyton Manning, he'd figure you were making fun of him. Moreover, it would never have occurred to him that he looks like Peyton Manning.

For example, I doubt if Karl Rove would like having it pointed out to him that he looks like a skinnier Lou Pearlman, the now-imprisoned boy band impresario, gay molester, and Ponzi Scheme runner. 

But, Lou would probably also hate having you mention to him that he looks like Karl. If you told Lou Pearlman through the bullet proof glass of the visiting room at his penitentiary that he kind of reminds you of Karl Rove, it would likely be the worst thing that happened to him all day.

Everybody is a special snowflake in their own minds.

32 comments:

Anonymous said...

Very interesting. My twin daughters appear similar but easily distinguishable. Most people look at me like I'm crazy when I tell them they are "identical". Then I usually have to explain the precise meaning of that term.

SeanS

Paul Mendez said...

Everybody is a special snowflake in their own minds.

I dated a twin. She and her sister looked identical (except for the, ahem, plastic surgery part). Same mannerisms, both lefties. Once, they independently went shopping for a dress to wear to a special family occasion and purchased almost identical items.

However, if you ever dared to point out these similarities or, God forbid, buy them matching gifts, they would screech, "I'm NOTHING like my sister!"

Black Death said...

The zygosity of twins is easily determined by the examination of their placentas, which should be performed in all cases of same-sex twins.

Anonymous said...

The rule is that you can tell someone they look like someone who is unambiguously extremely attractive. Otherwise keep it to yourself. An ex-friend once told me I looked like Carl Rove (I was heavier at the time). It stung.

George Terrell said...

Some years ago,a student of mine who had studied the genetics of the day asserted that since females have two X chromosomes, one, randomly chosen, is "silent". Therefore, about half of all female identical twin pairs are significantly more different than are male identical twin pairs. I have never seen this authoritatively verified. if it were true though, it might explain some things.

Anonymous said...

...people seldom appreciate having you point out to them that they look like some famous person.

This has been going on for years. Once or twice a month some random stranger will walk up to me and ask if anyone has ever told me I look like Richard Dreyfuss. I'm a good natured guy, so it doesn't tick me off as much as it might, but I swear, I look in the mirror, and I see only the vaguest generic resemblance.

However I truly cherish the time it came out this way: "You know, you look like that actor, Richard something, you know, Richard... Richard ... PRYOR!"

not a hacker said...

Ionce met a 33-ish lawyer who got upset when I told her she looked like Rosanna Arquette.

jody said...

are researchers still finding that twins (of any kind) score like 2 points lower on intelligence tests on average than other people of the same group?

wonder what the effect is in the womb of competing children. and does it accelerate for triplets and so forth. triplets even more likely to score slightly lower on intelligence tests, quadruplets even more?

wonder what the brainpower drain was for octomom's kids.

jody said...

my dad's sister has twins. they were very identical. they looked exactly the same and played the same sports too. they both picked soccer as their main sport in high school and played all the way through college. i could not tell them apart until they were in their late 20s and had diverged a good amount.

today one guy is a PHD in spanish and portuguese languages and is looking to become a university professor (i guess this makes him a doctor now, gonna have to start calling him Doctor Smith!)

the other guy is a gym teacher.

they got in a car crash 5 years ago and the guy who is a gym teacher now, his face went through the windshield and he got a huge cut vertically down his face that plastic surgeons tried to fix. made us all able to instantly tell them apart though.

Allison said...

Twin studies show twins raised separately have higher correlated scores on personality tests than twins raised together. Without the other one there to actively differentiate from, they act on their natural and therefore genetic tendencies.

Ray Sawhill said...

I was on a plane flight once and my eye was caught by this one guy ... As far as I could tell, he looked EXACTLY like me. I kept sneaking glances at him to make sure I wasn't being completely deluded. There were a few differences, but really we looked awfully similar. I finally couldn't help myself, and approached him and introduced myself, and ventured that I'd been struck by how much alike we looked. He responded with an expression of utter horror and disbelief.

Which one of us was more mistaken? I have no idea.

Anonymous said...

One thing for sure, all swipples might as well be multiple twins since they all think alike.

Anonymous said...

What about triplets, quaduplets, and quinteplets? What is the 'politics' among the kids? Among triplets, is it like two side against the one?

poultry inspector said...

@Ray Sawhill
Nabokov's novel Despair is a brilliant treatment of this theme of perceived likeness.

poultry inspector said...

I've often wondered if the Kray twins were really identical, as claimed. They were both homicidal gangsters and possibly psychopaths, but Ronnie differed from Reggie in being schizophrenic and homosexual. He looked considerably different from his twin in later years, but this could have been the effects of anti-psychotic medication.

Pouffiassei said...

@blackdeath

Common error. Most, but certainly not all, ident twins share a placenta, so examining the placenta will get you some idents incorrectly labeled as frats. I would bet anything that the Olsen twins are one of these cases, in interviews they always point out that they aren't ident twins but that seems like something a genotype-phentotype-ignorant ob/gyn told them based on his or her placental exam at their births. Looking at them it's hard to believe they aren't idents.

ricpic said...

Has there ever been a twin who became a recognized artist in any medium? My guess would be no. And the reason is because twins are the only humans who are not lonely in the existential sense. The need to breakthrough the otherness of the world by expressing ones separate isolate self doesn't exist for a twin, who goes through life with another inner self out there, in the world.

Dahlia said...

The most depressed I ever saw my step-mother get was when she was told she looked like Roseanne Barr... which she was told a lot during the show's reign.
Her: I love that show, she's so funny!
Them: (misconstruing this meaning and taking a gambit that it's safe) Yeah, me, too. You know, you look just like her!

I was in Kindergarten when "Annie" came out. My mother and other relatives loved that there was this hit movie about a little redheaded girl since I was a little redheaded girl. They told me how much I looked like her and wanted to buy the merchandise for me.

I loathed her and thought she was ugly; I especially resented being told I looked like her. As an adult, I can see she was quite pretty, but I just saw a mass of kinky, frizzy orange hair shaped into a ball.

I remember being about the only girl in my class who didn't have an "Annie" lunch box which the teacher asked me about!

Thinking about it now, I feel kind of bad for denying my mom that opportunity to indulge in some pride.

BTW, I just think that is so peculiar and human that only identical twins are ever wrong about their own twin's relatedness to them.

rob said...

George Terrell said...
Some years ago,a student of mine who had studied the genetics of the day asserted that since females have two X chromosomes, one, randomly chosen, is "silent". Therefore, about half of all female identical twin pairs are significantly more different than are male identical twin pairs...


The student was close to right. Fairly early in development, every cell with 2 X chromosomes 'randomly' inactivates one or the other. At each cell division inactivation is inherited, a real example of epigenetic inheritance. Female identical twins are much more likely to have biased X-inactivation than normal.

Luke Lea said...

I'm a fraternal twin. My twin brother and I have always been opposites: his eyes are brown, mine blue; his hair curly, mine straight; his lips were thin, mine thick; he could tan, I couldn't. In other words he had all the attributes I desired.

Looking back it is clear there was sibling rivalry for our mother's affection. He always won because (a) he was cuter, and (b) I was stronger and more physically aggressive. Childhood photos always show him with a smile on his face and a frown upon mine. :(

Still I remember my childhood growing up in the South as easily the happiest period in my life. We were absolutely care free, constantly together, and had liberty to go where, and as far, as we pleased. The only rule was be home by supper.

Which reminds me of one particular fight that ended in a draw. We were locked up in a clinch on the ground two blocks from home when Mother called for supper. We had to verbally agree not to attack before either would let the other go, after which we got up and walked home together side by side. .

Another time when we were about ten a boy in the neighborhood who was a couple of years older and quite a bit bigger picked a fight in the park across the street. He could have beat either of us up in a minute, he knew it, and we knew it. So without speaking a word -- I remember exchanging glances-- we knew our only hope was to attack him simultaneously. That we did and it turned out well. Another lesson learned, another bonding memory.

I love my twin brother to this day, and he is certainly devoted to me. We are still different, with different opinions, living very different lives in different parts of the country, but united by memories of a shared childhood that was filled with adventure and seemed to go on forever.

We get together on holidays and thank our lucky stars for the parents we had.

Anonymous said...

Have there been fraternal twins where one turned out mostly white and the other mostly black?

How did they turn out in life in terms of income? It would make an interesting study in blackonomics.

Londoner said...

Are maternal twins a disproportionately white phenomenon? I'm drawing a complete blank on prominent nonwhite twins, and don't recall having ever met any in real life. I guess white women do tend to have kids later, which I believe makes twins more likely.

I know a large family which included triplets - identical twin girls and (an obviously non-identical) brother. No one (them included) thinks of them as triplets - just as a pair of twins and a brother with no particular link to them. Which I suppose is not surprising really.

Also know twin sisters who maintain they are frats but are obviously mats - they look more alike than many confirmed mats do. The only question in my mind is over the fact that one is right-handed and one a leftie - is this atypical among identical twins or common?

Anonymous said...

I can't comment at MIglesias' site without signing on to a cult I don't necessarily want to join. But boy, what a bunch of pompous ignoramuses. Science is now come to this:
'If the glove don't fit, you must acquit.'
Gilbert P.

Anonymous said...

My identical twin father seems pretty happy to be an identical twin. I'd guess the snowflake business is primarily a female psychosis.

As an aside, the reasons for their slightly different voices, mannerisms and looks (noticable only to close relatives) have always been a curiosity to me. After close scrutiny I'm even able to tell who's who in childhood pictures so whatever it is that set them ever so slightly was probably pre-natal.

Maya said...

" Among triplets, is it like two side against the one?"

I've known 2 sets of triplets. One set, I knew as a child. They were 3 girls: 2 looked identical and the third one was much taller and looked obviously different. The identical-looking pair usually played together, and the third one played alone or with school friends.
The second set of triplets were my students in Europe, and their mother also hired me to come tutor them in math and English in their house. They were two boys and one girl. There, the division was by gender, obviously. The girl was more interested in shopping and dance, and the boys played soccer and did martial arts. I saw the boys out often without the girl. Here's what I often wondered... The boys were very different too. One had a regular semitic look to him (they were Arabs)-hooked nose, puffy lips, outer corners of his eyes were pointing slightly downward and he was short. The other boy could have been a movie star- tall, lean and broad shouldered with a beautifully sculpted face. The tall boy was a lot more confident, smiled more and did better in school. So I couldn't help but ask myself, does it completely such to be the shorter boy triplet? Is being constantly compared to a better looking, more successful sibling a lot worse when you go through the comparable experiences at the exact same time?

Maya said...

"Have there been fraternal twins where one turned out mostly white and the other mostly black?

How did they turn out in life in terms of income? It would make an interesting study in blackonomics."

Would it? These twins would obviously be of mixed heritage, so it would be impossible to know whether their success (or lack there of) is due to their phenotype or the invisible traits the gene lottery granted them. Looks can be very deceiving.

Andrew Gilbert said...

"Has there ever been a twin who became a recognized artist in any medium?"

I can only speak for jazz, my area of interest, but there are numerous examples of identical twins who are stellar musicians. Off the top of my head there’s percussionist Alex and guitarist Nels Cline (now with Wilco), saxophonist Marcus and drummer E.J. Strickland, pianist Pascal and saxophonist Remy Le Boeuf, and trombonist Alan and drummer Mark Ferber…

rob said...

Londoner said...
Are maternal twins a disproportionately white phenomenon? I'm drawing a complete blank on prominent nonwhite twins, and don't recall having ever met any in real life. I guess white women do tend to have kids later, which I believe makes twins more likely.


I assume you mean identical twins, unless that's a Britishism. I think identical twinning rates are close to even across races, unlike fraternal twins. Blacks have more fraternal twins, then whites, then Asians. Pretty much what one would expect from parental investment.

As for prominence, twins (both sorts) are dimmer than normals. Like 5 points flat out. They controlled for prematurity and birth weight and then the difference was 4 points at age 9. So it's not just cuz their born earlier and smaller, there're probably effects of sharing a womb. After all, there are reasons people don't have litters. The study was on old data from Scotland, so I doubt race influenced it. Now that IVF-induced multiple births are getting pretty usual, and IVF mothers are smarter(on average: not Octomom) there are probably lots of twins punching below their genetic capacity.

If I were a liberal creationist, I would seize on that against twin studies: their developmental environment is deprived, so generalizing from them to everyone else is pretty iffy.

Anonymous said...

OT. Effects of Fukushima radiation far worse than previously thought.

Anonymous said...

Peyton Manning? Huh? Steve, you think Manning is bad looking?

I mean, when he speaks, he sounds as if he has a perpetual sinus infection, probably the result of several broken noses and a deviated septum, but he's not a bad looking guy at all, I don't think.

Actually, I think a lot of guys might enjoy being told they look like Manning--he's wholesome looking, very tall, an has an aura of success about him due to ....well, his success.

David said...

>The rule is that you can tell someone they look like someone who is unambiguously extremely attractive. Otherwise keep it to yourself.<

It does sting. I don't know how many times blacks have told me they mistake me for some other non-famous non-extremely-attractive white guy they know. "I thought you was x!" (followed by screaming laughter). We all look alike, apparently.

Steve F said...

I went to school with those guys. Actually, I only remember the QB, since I was an athlete. Maybe I saw the other one and mistook him for his brother, though.

Another Wabash College grad made it to the big time. :)