Two of a Kind

This piece about my twin sister Sarah and I was written for my Viewpoint Journalism class last fall. It's really long and not my favorite, which is why I am posting it first, in hopes that no one will ever get this far back in the archives...




“Can you read each other’s minds?”

“When she gets hurt, do you feel pain?”

“Do you guys have special powers?”

As a twin, I’ve gotten used to these inane questions (the answers are no, no, and what the hell are you talking about?). From as early as I can remember, my fraternal twin sister Sarah and I were inundated with queries and expressions of awe at our twinship. I didn’t question it then, and was happy to revel in the attention. It is only recently that I have thought to more closely examine this phenomenon, to wonder why people seem to view the twin relationship as inherently special, and whether they are right.

In studying how twins are raised, researchers have found that parents tend to fall into one of two categories: “twin-oriented,” those that focus on the similarities of their children, playing up their twin-ness, and “differentiation-oriented,” those that accentuate differences among twins, trying to give each a sense of individuality. My parents definitely fell into the latter category: though baby pictures confirm that it was easy to tell us apart based solely on the size difference of our heads – Sarah’s wispy blond dome could easily be mistaken for a moon of my hulking planet of a noggin – we were always dressed in different colors. Instead of sharing a single cake for our birthday, each year my mother would decorate a layer for each of us, our own unique, if slightly downsized, sugary circle of celebration. Pictures from our first birthday confirm this practice was in place from the beginning, our tiny smiles each lit up by our own set of candles.

Interestingly, studies have shown that the differing parenting approaches are dictated by the twins’ behavior, rather than vice versa. Twins who act alike are more apt to receive twin-oriented parenting, while dissimilar twins will likely be raised in a differentiation-oriented manner. From a young age, Sarah and I were diametric opposites in terms of disposition. A notoriously fastidious baby, I would make a fuss over even a drop of spilled apple juice while next to me Sarah would swim contentedly in her dinner, grinning a wide tomato sauce-stained smile and ignoring the strands of spaghetti that had somehow slithered their way into her hair. Home videos reveal me to be either camera-shy or a baby stoner, gazing silently or retreating from view while Sarah sought out the video camera, babbling incessantly into the lens.

I’m not sure whether my parents’ decision to dress me in blue and Sarah in pink was prescient or the creation of a self-fulfilling prophecy, but our childhood interests were as distant as our hat sizes. The prototypical tomboy, I played every sport I came across, eschewed Barbie dolls in favor of Nerf weapons, and almost made my mother aspirate her iced tea one summer afternoon when I announced that I would be wearing a tuxedo in my wedding. Sarah, on the other hand, loved lace dresses and stuffed animals, knew the first and middle names of every one of her two dozen Cabbage Patch Kids (many generously donated by me, Hater of All Things Girly), and filled her days running a daycare for her little plastic charges. When asked to join in, I would agree only to be the daycare’s secretary, manning a phone that never rang. But our interests weren’t completely mutually exclusive; we both liked to gather Sarah’s plush menagerie and stuff them between the two foam pads that served as our shared mattress, forming a hill of softness on which we would perform various ill-advised acrobatic stunts.

As much as my parents did their best to individualize us, the outside world seemed intent on defining us by our twinship. Courteous enthusiasm upon our introduction as two sisters gave way to a bubbly excitement when it was revealed that we were, in fact, sisters born on the same day. “Ooh, you’re twins?” became such a familiar phrase that it took on the timbre and cadence of a lullaby. Once they discovered our genetic little non-secret, our classmates and their previously uninterested parents suddenly became fascinated by us. They squealed over newly perceived (and often exaggerated) similarities, and adults of perfectly good vision began mixing us up, suddenly unsure who was whom.

I remember even at that age thinking, what’s all the fuss about? Dr. Nancy Segal, a professor of development psychology and director of the Twin Studies Center at California State University, Fullerton – and a fraternal twin herself – says that people are generally interested in twins because they are counterintuitive to our concept of individuality. “Identical twins fascinate people because they are contrary to expectations of individual uniqueness in appearance and behavior – they are separate individuals, but more alike then anyone else,” Segal says. The children who grew up in my generation, one that emphasized self-esteem and celebrated individuality, whose elementary school classrooms were plastered with posters proclaiming “I Am Me!” and whose students’ self-oriented projects were littered with gold stars, may be even more intrigued by the idea that there could be someone else in the world who looked, and even behaved, the same way as them.

As much as we were treated as individuals in our own home, outside of it we were always a set. Our parents strove to make us feel special and unique, so we played sports, joined clubs, or fostered a musical talent to express and define ourselves. Although I played a different sport every season and Sarah was a musical whiz, to others we were still twins first, and Amy and Sarah second. It was a strange and paradoxical thing, to feel defined not by any individual talent or distinction, but rather by my relation to someone else. I was unique because we were the same. I learned early on to accept that as a twin, you stand out from the crowd, but the spotlight never shines on you alone.

Of course, as a child I didn’t much resist the emphasis on our twinship. Being known as a twin meant attention and notoriety. As just myself, I probably would have made friends at school, but being a twin in elementary school was like being popular in high school – I may not have been liked by everyone, but they all knew who I was. It made me proud. Like a gambler who garners a sense of accomplishment from winning Keno, I found myself taking credit for the genetic randomness of life, and relished the gifts that it brought me as if I had actually earned them.



The enthusiasm of breathless new acquaintances isn’t the only reason that twins are made to feel special in our culture. The study of heritability – the extent to which traits, like intelligence or aggression, are influenced by our genes – is a major part of current genetic research, as scientists try to place everything from eye color to handwriting to alcoholism somewhere on the nature-nuture spectrum. And one of the favored ways to look at heritability is using the classical twin study paradigm. First introduced in 1911, it compares identical twins to fraternal twins. Since identical twins share one hundred percent of their DNA and fraternal twins about fifty percent, comparing the two can give a strong indication of whether a trait is genetically influenced.

For example, if identical twins almost always show the same degree of shyness (both are very shy or both are very outgoing) and fraternal twins vary more, then one can reasonably conclude that genes are a large factor in the trait of shyness. These studies have helped researchers determine that genes play a big role in a wide array of biological traits, from blood pressure to attention-deficit disorder, but have little influence on others, like Parkinson’s Disease. They have also been helpful in determining the heritability of psychological traits. Major personality traits (openness, agreeableness, extraversion, neuroticism, and conscientiousness, known collectively as the Big Five) have been found to have a modest genetic origin from twenty to forty-five percent. Attitudes such as happiness and shyness also have high degrees of heritability, while mate choice has been shown to depend very little on genes.

Intelligence, as measured by IQ, has been the subject of many twin studies. The average correlation of IQ scores (measuring how similar one subject’s IQ score is to another’s; a correlation of 1 indicates a perfect match, while 0 indicates no connection at all) is .86 for identical twins, .60 for fraternal twins, .46 for non-twin siblings, and .15 for cousins. This general pattern follows for most traits: identical twins are more similar than fraternal twins, who are in turn closer than non-twin siblings and more distant relatives. This evidence presents a strong case for a high genetic influence on our individual traits.

One of the most interesting findings from this intelligence research concerns the change of genetic influence with time. Several studies that have found that genes actually play a bigger role over time, accounting for about 60% of similarity in adults, as opposed to approximately 50% in adolescence and 30% in early childhood. This is counterintuitive to our natural assumption that environment would play a greater role as people age and tend to branch off further into their own individual lives. Instead, Dr. Segal says “it appears that with age we acquire greater freedom to fashion our own environments in ways that are more compatible with who we are, and in doing so we become ‘more like ourselves’ every day.” In the case of identical twins, becoming more like one’s self also means becoming more like one’s twin.

This idea is mirrored by a 2006 study in the Journal of Personality and Social Psychology that examined the twin relationship in terms of attachment. The researchers compared feelings of attachment to different “targets” (mother, father, sibling, and romantic partner) over time. Twins and non-twins showed similar patterns of attachment to all the targets except siblings. While non-twins reported feeling less attachment to their siblings over time, twins said they actually felt a stronger attachment to each other as they aged.

Some have objected that such twin studies are flawed because twins are usually raised in the same environment, which makes it impossible to tell if a similarity is due to their similar genes or the household they also share. The Minnesota Study of Twins Reared Apart was started by Dr. Thomas Bouchard in 1979 to look at the rare instances where twins are raised separately. Many of us have heard stories of twins reared apart that upon reuniting discovered eerie similarities. One of the best-known of these cases is that of Jim Springer and Jim Lewis, twins from the Minnesota Study who were separated at infancy, raised apart, and finally reunited after thirty-nine years. The pair, known as “the Jim twins,” revealed some astonishing similarities: both had been married twice to women of the same name (Linda and Betty), had a son with the same name, and had even driven the same model car to the same three-block Florida beach neighborhood for vacation – without ever meeting. These extraordinary similarities highlight the strength of the genetic tie between the two men. Their story also amplifies the mystique of twinship; the congruence between them feels almost supernatural.

Twin studies have also become extremely important to the new hot topic of epigenetics, which is about the way that chemical alterations of DNA affect how certain genes are expressed. Scientists are learning that in addition to having different genes, different people can have the same gene which manifests itself differently based on how it interacts with other chemicals in the body. Take hair color, for example. Two people may have the same exact gene coding for the same exact brown hair color, but because one person’s DNA is modified differently (a few methyl groups have been added to it, say), the two people can end up being different shades of brunette. Identical twins play a pivotal role in epigenetic research. Since they have the exact same set of DNA, any differences in physical traits that are highly or totally genetically-influenced (like hair color) can be attributed to epigenetic changes in the expression of these genes.

In the end, these studies leave us with a general sense of a strong genetic influence sprinkled with exceptions and qualifications, emphasis on the varying degrees to which environmental factors play a role, and the acknowledgment of natural variability between all individuals. More relevant than the actual results of these studies is the scientific community’s increasing recognition of the value of twins in helping sort out the whole mess. The idea that by studying twins scientists might finally solve some of biology’s most persistent and complex puzzles (for instance, are we genetically predetermined to be anxious/gay/math whizzes? Or is it because we grew up in overindulgent/violent/emotionally repressed households?) gives twinship an air of importance, of necessity. Science needs twins in order to unlock the mysteries of genes that extend deeper than the sequences of DNA which comprise them. This reinforces the notion that twins are special, but not because of any individual distinction or achievement. Only as a pair, as a full set, can they help illuminate any of the shrouded secrets that lurk within the twisting double helices of our genetic makeup.



Some people believe that we tend to view twins as special because they manifest an ideal human relationship: built-in partners who fully understand and empathize with each other. While most people struggle to establish compatible long-term friendships and romantic partnerships, there is a sense that twins are connected with their soulmate from birth. Scientific study of such an intangible concept is difficult, so there is not a lot of evidence to support or refute this idea. But there is some.

In her book, Entwined Lives: Twins and What They Tell Us About Human Behavior, Nancy Segal has a name for the relationship unique to twins: friendship extraordinaire. In her observational research, she has watched twins interact in different cooperative and competitive environments. On cooperative tasks, such as putting together a jigsaw puzzle, identical twins were more likely to complete the task than fraternal twins, who more often acted like other children – shoving each other and hoarding pieces for themselves.

In a study of competitive tasks, twin pairs were asked to complete mathematical and matching tasks both separately and in the same room. Identical twins performed more alike when working in the same room, and identical twins who had performed faster working alone slowed down when in the same room to allow their co-twin to catch up. This phenomenon was absent in fraternal twin pairs. Segal concluded that identical twins showed “a greater restraint of selfishness” than other children. Even at a young – often very self-involved – age, twins make space for their co-twin in their lives. Perhaps this marks a distinct aspect of twinship; while most children have to be explicitly taught social concepts such as sharing and considering others’ feelings, twins adopt these ideas more intuitively, maybe even unconsciously. The difference is like using a natural limb versus an artificial one. We learn to use our hands naturally, through intuition and experience, while learning to operate a prosthetic device is an intense, highly cerebral and deliberate process.



Though we may have an urge to idealize the identical twin relationship as perfectly harmonious, Segal points out that many identical twins view each other as rivals with whom they constantly battle. However, she notes that “even ‘warring’ twins may be inseparable due to mutual understandings.” Though they may be sparring partners, they are partners nonetheless. Segal suggests that “identical twins may, thus, come closer than anyone else to achieving the coordinated, harmonious relations for which we all strive.” Though some dysfunctional couples may disagree, the ability of two people to be at odds with each other without disrupting feelings of intimacy is rarely found outside the confines of identical twin relationships.

Sarah and I were close growing up, but we were also each other’s biggest bully. As possibly the most studious 5th grader ever, Sarah carried around twenty pounds of books in her backpack, and I took great delight in exploiting the weight imbalance the behemoth created. I would seize every opportunity I could to give her a gentle shove or pull, which inevitably would send her stick-thin figure stumbling to the floor. She got her shots in too; like a pro wrestler notorious for a devastating move, Sarah was known (at least by me) for her “clawings:” she would dig her nails into my leg and drag them until she drew blood. Though neither of us has forgotten these memories, they are brought up now with laughs rather than tears, both of us incredulous, and slightly ashamed, of the damage we used to gleefully inflict on one another. But these recollections of our mutual torture lack the sting of pain or guilt that accompanies so many of my other childhood memories. We never officially apologized to each other for anything. We didn’t have to.



Evolutionary psychology, with its basic tenet that animals behave in ways which will allow them the highest possibility of passing on their genes to future generations, can explain many of our collective behaviors. It can also provide insight into twin relationships. For a time, scientists weren’t sure how well this theory fit with the many acts of altruism – helping out someone else at a cost to one’s self – observed in nature. After all, if animals are just driven to reproduce and pass along their genes, why would they take risks for anyone else? In 1964, William Hamilton, a preeminent evolutionary biologist, addressed this problem when he published a range of studies in which he proposed the concept of inclusive fitness. Inclusive fitness is the idea that an animal will help close family members, with whom it shares many genes, in order to ensure that those genes get passed on, even if not through it. It is essentially the “selfishness” of the gene (wanting to be passed on somehow) that manifests itself unconsciously in altruistic behavior. This has been supported by studies which show that animals act more altruistically toward close family, such as siblings or offspring, than toward kin with whom they share fewer genes, such as cousins.

Based on this idea, it would follow that identical twins, who share all of their genes, should be equally as concerned with their twin’s prosperity as with their own. Identical twins are completely unique in this equal degree of self-interest and interest in another. This is not to say that a twin necessarily sees his co-twin’s life as equally important to his own (we all have a self-preservation instinct), but the similarity is much closer than that of any other human relationship. As Segal writes, “I do not believe there is a special process for responding to one’s identical twin. Instead, increased closeness between twins may be an extension of the general principle of directing increased altruism toward close relatives.”

Twins are also sometimes seen as two sides of the same coin, yin and yang. While I certainly don’t think of myself as a bad person, if the good twin-evil twin dichotomy really holds true, Sarah would be the one dressed in gauzy white. She is too nice to take shopping (I blame her for a closet’s worth of bad ideas, including ill-fitting Bono-esque sunglasses and a pair of overalls that she said looked “um, really cute!” on me) and has trouble being hostile even when she tries. In college, she used to complain about one of her music theory professors, an unpleasant woman who arbitrarily failed half her students each semester. Once Sarah proudly told me how she had banged on her professor’s office door late one night to vent her frustration. “I just knocked on her door,” she said, “but I would have rather knocked on her face!” It was one of the meanest things I have ever heard her say.

In the seven-plus months that she was unemployed after college, she never missed a single one of her monthly donations to the ASPCA. In contrast to her roommates who hung pictures of drunk friends and racy images of a shirtless Justin Timberlake or Ralph Lauren model, her college dorm room was decorated with a shrine-like photo collection of our beloved black lab/daschund mix Pete and a single poster of a fully-clothed LL Cool J (“just look at those lips!” she’d say). It’s this special brand of pure-hearted, unintentional hilarity that earned her the nickname “Dory,” Ellen DeGeneres’s character in Finding Nemo.

If she were just my sister rather than my twin, I’d probably find Sarah’s angelic persona annoying. I imagine I’d be faced with the “why can’t you be more like her?” question, to which I have no good answer. But it turns out that there are upsides to sharing the spotlight. As her twin, I can claim partial ownership instead of obligation. Rather than a pair of contrasting images, our portrait is shared, so I get to bask in the diffused light of her halo.



The finding discussed earlier that twins become more attached to their co-twin as they age is of particular interest to me now as I move into adulthood. Sarah and I have both changed a great deal since getting our first tastes of twin celebrity. She teaches music in a New Jersey elementary school, while I stare into a microscope for a living in D.C. My Ninja Turtle action figures are long gone, and she uses pasta for sustenance rather than accessorizing.

We talk and see each other regularly, but our contact is much less frequent than it used to be. Though she may take up a smaller part in my life, her role has become more important. As I experience the natural paring down of significant relationships that often occurs in young adulthood, I rely on her more for the emotional support that used to come from my parents, mentors, and the comfort of a stable childhood. She is the only person in my life who remembers all the funny stories from my childhood, and a glimpse at of our Facebook walls reveals a back-and-forth of inside jokes years – and in some cases decades – old. She is the only keeper of my deepest secrets, and the care package she sent me in the wake of my first big breakup did as much for my spirits as a dozen cathartic boy-bashing sessions with my friends. Reading the endearing loops of her child-like handwriting, I could hear her voice assuring me that “breakups are the fucking worst, but I swear it gets better.” It was the first time I actually believed I would be okay.

If the research on twin relationships has come to any kind of coherent conclusion about the special-ness of twins, the verdict is limited to identical twins. Fraternal twins like me are often viewed as the control group, having as much DNA in common as non-twin siblings. But studies have also shown a consistently higher degree of similarity in fraternal twins than other siblings.

So, since science gives me only vague and inconclusive evidence about the distinctiveness of my twin relationship, I look to my heart for a more fulfilling answer. Even as I encounter fewer people who are aware that I’m a twin, and so feel less externally defined by my twinship, my perception of our connection as special persists. Observing and experiencing other relationships has reinforced my thought that ours is unique, though I can’t quite put my finger on what exactly sets it apart. I have been guided by great parents, reveled in the intimacy of close friends, and been warmed by the fire of romantic relationships. But Sarah is different. We are different. I can’t explain why, and I don’t fully understand it myself, but it is true. And it is special.