Psychology Today Blogs - Twofold

Fraternal Twins--The Hidden Pairs

Nancy L. Segal — Wed, 07 May 2008 15:55:10 -0700

I was on the Today Show today, May 7, 2008. The taped piece focused on studies from two separate laboratories. The first study concerned research on twins’ social relationships, conducted in my lab at California State University, Fullerton. In general, I have found that identical twins show closer, more cooperative behaviors than fraternal twins when working on a common task. The second study concerned new findings that identical twins may show actual DNA differences (what are called copy number variations--CNVs), conducted at the University of Alabama. Twins with DNA differences may help us understand what factors trigger illness or other conditions in one twin, but not the other. However, there were twins in that study who showed DNA differences, but who did not differ in other significant ways. These two studies are related in that DNA differences between identicals could be associated with behavioral differences; these could ultimately affect the twins’ social relationships. The two taped segments were followed by live interviews with two sets of identical twins, one male and one female. The male twins were current and past football greats, Ronde and Tiki Barber. Tiki Barber left the New York Giants last year to join the Today Show as a special correspondent. One of them commented that they do not try to do things the same way, but often end up doing them alike. As examples they cited buying the same item—and of course ,they play/played football. The female twins were my colleague, Dr. Eileen Pearlman, and her twin sister Elaine. Interestingly, Dr. Pearlman noted that as the slightly leaner twin from birth, she was referred to as “skinny”—and when she sees her twin even today she feels compelled to watch her diet to remain in that role. Both pairs also emphasized the importance of separating twins so that they feel prepared for the inevitable separations that occur later in life, e.g., school, work, marriage. I would qualify that, especially with reference to twin type. First, as indicated above, identical twins tend to be closer than fraternals and should, I feel, be allowed to enjoy their relationship. Most identical twins celebrate their twinship, emphasizing the great understanding and comfort it affords. I fully support the state-by-state movement, currently in play, that is developing legislation that would give parents a significant voice in their twins’ classroom placement. Too often, schools demand that twins be separated, when it is not in their best interests. Of course, some periods of separation for twins are needed—but in their own ways, each set will reveal what is appropriate for them. Fraternal twins may naturally gravitate toward their own friends and interests, but even they may suffer the effects of premature separation from one another. The bottom line is that the needs of each set should be handled on a case-by-case basis. This brings me to the final point. Fraternal twins are far more common than identical twins, yet the media focus on the latter. Understandably, their matched appearance makes for great visual effects. But science could not proceed without the presence of fraternal twins, that all-important control group for comparing twin similarity. (Greater resemblance between identicals than fraternals demonstrates genetic influence on the trait in question.) More families are raising fraternals than identicals and are in need of information and support, yet they and their “hidden twins” are overlooked. There are some fascinating varieties of fraternal twins that many people are unaware of—twins with different dads; twins who appear to come from different ethnic groups; and more. We also know a lot about the causes of fraternal twinning, a subject that would make for great viewing. I say this mostly as an investigator--not as a fraternal twin.

Quadruplet Varieties

Nancy L. Segal — Thu, 24 Apr 2008 13:03:47 -0700

Human interest in higher order multiple births can overwhelm the scientific side of things. In mid-April, a Towson, MD couple delivered an unusual set of quads—identical triplet boys and a fraternal male co-quad. The parents, eager for a child, sought artificial reproductive technology (ART), known to be associated with multiple births. In ART, several embryos are usually implanted in the uterus in the hope that at least one will develop into a fetus. (Current trends are toward limiting the number of embryos to avoid the risks of multiples.) The Towson mother had had only two fertilized eggs implanted, but one split twice, giving rise to identical triplets, and the other fertilized egg developed as well. I envy this family their living laboratory. Their unique foursome yields an informative series of genetically informative kinships: three sets of identical twins and three sets of fraternal twins if all the boys are pairs in every possible combination. Given that the quads share the same rearing environment, it will be fascinating to witness the developing similarities and differences in their behavioral and physical traits. Based on the existing twin literature, we can expect the identical twins/triplet to be more like each other than either is to their non-identical brother. The unfolding social relationships will also be fascinating to observe. Research shows that identical twins enjoy closer social relationships, on average, than fraternal twins. It may be that the fraternal quad will feel left out of the identical triumvirate. On the other hand, he may be an assertive leader, directing inter-quad activities. I was fortunate to be able to observe another young quadruplet set close up. Benny, Nicky, Matt and Mike were born to a Canadian couple, Mandy and Rob, who wished to add one common child to their family. (Each partner had had a daughter in a previous relationship.). The “quad boys,” as they are called, were naturally conceived and include a different intriguing array of brothers. They are composed of two sets of identical twins—Benny and Nicky and Matt and Mike. These four present a somewhat different living laboratory, convincing their parents that nature counts for a great deal in human development. At first Mandy tried to decouple the identical twinships by arranging for the fraternal twins to be roommates. This experiment failed miserably because the behaviors and preferences were matched within identical sets, but at odds within fraternal sets. The social affiliations among these young boys are also revealing. Matt and Mike are joined at the hip. It is likely that Nicky and Benny would be too if not for Nicky’s cerebral palsy. Nicky has a fairly severe case of the condition—still, it is his identical twin brother Benny who is his most constant companion. This is interesting, since the boys know nothing about genetic relatedness and no one pressured Benny more than the other two to look out for his brother. We can learn a lot about what drives human social relationship just by watching these four act naturally. Twin studies have been ongoing for years, yet there are few formal studies of triplets and more. It is likely that this will change, given the new reproductive technologies and improved methods for monitoring multiple birth pregnancies.

Unusual Twins and Sibs—Who Are They?

Nancy L. Segal — Wed, 16 Apr 2008 15:50:10 -0700

When I was eleven or twelve years old my parents enrolled me in a summer camp in upstate New York. One of the regularly scheduled activities was sitting around the evening campfire learning new songs. I loved the words and melodies and sang them often (mostly to myself), even during the weeks and months after camp ended. One song particularly fascinated me--it was “I’m My Own Grandpa,” a fifties’ hit popularized by the great Guy Lombardo. The song tracks the hilarious series of paradoxical relationships that begin when the step-daughter of a newly married young man marries her new father’s father—making him his son’s son-in-law and the daughter (his wife) his son’s mother (as well as his daughter). Five verses and ten genetic calculations later, he realizes--with shock and horror--that “as husband of my grandmother, I am my own grandpa.” Hence, the title of the song.

That little song is more relevant today than it ever was in the fifties. New medical technologies, adoption policies and (re)marriage practices are rapidly changing the faces of families. Ordinary parent-child and brother-sister relationships have become extraordinary and difficult to define. Some mothers are bearing artificially conceived babies who may be related to both parents, one parent or neither parent. Who is the father, and is there more than one? Transplanting an identical twin’s healthy testis (or ovary) into his (or her) infertile co-twin has allowed these siblings to successfully conceive. But are the aunts and uncles of these children still aunts and uncles, or are they mothers and fathers? China’s One-Child Policy led to the abandonment and adoption of thousands of female babies, including twins. Young twins adopted by different families acquire different sets of relatives, so that one twin’s sibling is not her co-twin’s sibling. But what is she? Rare identical twin pairs include one twin who underwent sex reassignment surgery. Are these twins still twins and, if so, are they still identical? Possible human reproductive cloning may offer couples a child-bearing option that would produce children genetically identical to one parent. These parents and children are not twins, but what are they?

Here are my responses to some of the questions posed above; I imagine that some people will have a variety of views on these topics.

1. In my recent book, INDIVISIBLE BY TWO, I described the case of identical twins, Marcy and Tracy. Tracy was unable to conceive, so Marcy delivered two daughters for her sister. She did so by becoming pregnant via artificial insemination using her brother-in-law’s (Tracy’s husband) sperm. The twins were genetically the same, so that the children were as closely related to Tracy as if she had conceived them naturally. A DNA test could not distinguish the mother from the aunt—but Tracy was clearly the mother in this case as she raised the children from birth.

2. I discovered a fascinating case of identical male twins, one of whom was infertile due to anorchia, the absence of testes as birth. However, a testicle transplant from his identical twin enabled him to have children. The recipient twin was the biological father of his children as he was responsible for the conception--even though a DNA test could not distinguish the father from the uncle.

3. I am conducting a study of young Chinese twins, adopted separately as an indirect result of China’s One-Child Policy. This policy restricts child-bearing to one child in urban areas and to two children in rural areas. The society favors male children, so females are often abandoned, leading to separation and foreign adoption of some twin pairs, mostly female. This situation generates an array of relationships for which we lack names. For example, if one twin has another sibling, this sibling becomes more like a cousin to the twin sister because they are not reared together. This situation is highly unusual because twins typically have the same siblings!

4. There are rare pairs of identical female twins, one of whom undergoes sex reassignment surgery, believing that they were born as the wrong sex. In my view, these twins are still twins. I have witnessed wonderfully warm and supportive relationships between a number of such sets. I also work with twins whose twin have passed away, and continue to regard these “twinless twins” as twins. Being born a twin is central to one’s identity.

5. Human reproductive cloning became a possibility with the 1996 birth of Dolly, the cloned lamb. Many people have speculated as to the nature and consequences of relationships between adults who might raise cloned children. It is indeed unfortunate that references to such individuals have included terms such as “genetic twin” or “delayed twin.” In fact, they would not be twins at all! Elsewhere, I have set forth some criteria for what constitutes twinship. The main features include being conceived at the same time, being gestated in the same intrauterine environment, being born at the same time and being a member of a common cohort. None of these features would apply to cloned parents and children; thus, they cannot be twins.

I will end with a curious story of an older twin who contacted me over the Internet. It seems that his mother (who already had several children when he and his identical twin brother were born) was ill, so she decided to give one twin away for a while. This twin ended up being cared for by his aunt. The aunts also had a son, so the twin was raised with his cousin as though his cousin were a brother. The families met occasionally and when they did he had opportunities to send time with his identical twin—who now seemed more like a cousin!

It appears that whenever twins are involved, relationships take on a novel twist. At the same time, a scientific eye can discern important information from these unusual kinships.

For example, these separated twins were never studied, but based on published research, it is likely that the twins were more behaviorally alike than were the one twin and his biological cousin—despite the fact that they were raised apart. This underlines the fact that genes contribute to all phases of human behavioral development.

Sports-Minded Twin Pairs

Nancy L. Segal — Tue, 25 Mar 2008 15:03:15 -0700

Now, in the midst of March Madness and the upcoming Beijing Olympics it is hard to ignore the many elite athletes who come packaged as identical twins. These elite sets combine the best of human interest and great science. First, it is difficult to imagine two people so closely matched for rare talent. Second, just by acting naturally, these twins can tell us a great deal about the origins of athletic performance and sports interest. I came across a recent twin case that might truly make Olympic history. In early March 2008, one of the Molina twins from Commerce, California (Oscar) was in competition in Part-au-Spain, Trinidad, hoping to secure a place on Mexico’s Olympic boxing team. He did not qualify based on that event, after losing to a Cuban competitor; however, he can try again next month in the final regional qualifying boxing competition in Guatemala. Interestingly. Oscar has a twin brother, Javier.

It is difficult to know if they are identical or fraternal twins—pictures show them looking a lot alike, but just different enough so that they could be similar-looking fraternals, as well as slightly different-looking identicals. Javier will represent the United States at the 2008 Olympics. The bottom line is that if both twins succeed, this will be the first time that twin brothers will represent different nations in the same Olympic event.

How did this all happen? The twins’ family does not believe in competition between family members. Consequently, at the Olympic trials, the slightly heavier twin (Oscar) entered a higher weight class, lost by a point and was dropped. However, Oscar can play for Mexico because his parents were born there; Olympic rules allow children to compete for the country of their parents’ birth. Should the Molina twins participate in the 2008 Olympics, they would enter into different weight classes so would not be competing against each other. (Note: A larger piece on these twins, and additional references from which the information was drawn will appear in a forthcoming issue of the journal, Twin Research and Human Genetics.) Natural twin experiments in athletic skill are going on all the time, in neighborhoods, in recreational centers and on college campuses. I have discovered six identical twin sets on my campus, two in wrestling, two in soccer, one in gymnastics and one in track. How do these college twins explain their matched abilities? They say that they excel because they have had a “24-hour practice partner,” whereas their friends have not. I was not surprised to hear this because it is easy to link performance to practice. Practice and training are essential to excellence in sports, but they are only partly responsible. The other part of the story concerns the genetically influenced traits that athletes bring to their pursuits—muscle strength, running speed, reaction time--as well as the intellect to strategize and the motivation to succeed. However, neither behavioral nor physical traits alone make a great athlete. It may be that tiny disparities in training or in stamina--or in one’s sense of timing--make the difference between first and second place.

Performance differences between identical twins are actually more interesting to researchers than their similarities because they tell us what—and to what extent-- non-genetic factors (e.g., practice and training) are important for the rest of us. Coaches working with teams say that the rapport among the members is crucial for success. Five great basketball players may fail to accomplish what five less talented players can do if the latter are more sensitive to their teammates’ abilities, personalities and decision-making skills. Coaches who have worked with identical twins are impressed with the unspoken understandings that the twins display both on and off the field. Twins themselves say that their intimate knowledge of one another lets them easily anticipate what their co-twin is doing and thinking and, ultimately, whether he or she will pass the ball or attempt a shot. I have heard this from many twins, most recently from a California State University student who, along with his twin brother plays on the school’s soccer team.

Identical twins also have a unique sense of competition with one other--if one gets ahead, he or she eggs his sibling on (“If I can do it you can do it”), until they reach the same level. Identical twins are also surprisingly generous with their pride and happiness if one wins at a competition. When skiier Phil Mahre appeared to capture the Olympic gold medal on the slopes in 1984, he told his twin brother Steve, “Here’s what you have to do to beat me.” Maybe coaches and trainers should pay closer attention to what twins are doing in order to lift team spirit. (See Chapter 11:” Two-Base Hits and Triple Toe Loops: Physical Growth and Athletic Prowess”, in my recent book Entwined Lives for additional information and references on this topic.)

Twin Types—What Type Are You?

Nancy L. Segal — Sat, 15 Mar 2008 15:37:57 -0700

Many twins and their families are uncertain about what type of twins they are or have – identical or fraternal. Recently, I have had some rather fascinating experiences with twins along these lines. I was contacted by one member from a fifty-four-year-old female twin pair—I will call her Sally. Sally and her twin sister, Susan, had always believed that they were fraternal twins. This is what they had always been told; after all, the delivering physician had confirmed the presence of two sacs. However, about eight years ago, someone asked Sally why she was so sure that she was a fraternal twin. This person, an identical twin himself, was part of an opposite-handed pair and he noted that Sally was, as well. (Note that approximately 25% of identical twins show such mirror-imaging effects, often due to delayed splitting of the fertilized egg. At the same time, fraternal twins can also differ in hand preference, associated with inheriting different sets of genes form the parents. Therefore, differing in this trait is not conclusive with respect to twin type, or what scientists term zygosity.) The twins birthday is in February 2008, and Susan gave Sally a DNA test kit as a gift. The twins had considered DNA testing prior to this, but the cost was prohibitive; now testing can be done through the mail with the help of many genetic laboratories for about $125.00 per pair, simply by providing a saliva sample. The twins sent in their sample, waited several weeks, then called the lab. Susan was calm, while Sally paced back and forth. She was certain that she and Susan were fraternal twins--being fraternal felt normal--but she worried that they might be identical because then she could not tell her mother who was deceased. This would make her feel “privy to information that was not mine.” The news was that the twins were identical. Sally looks at Susan differently now. She claims that she has never felt closer to her sister, despite their life style differences (one twin is married and the other travels the world.) “I did not think it was possible to feel any closer—because we were so close before.” Susan and Sally reminded me of another twin pair, my high school friends, Barbara and Judy. I sat next to them in many classes because our last names were close alphabetically. I always believed that they were identical twins, yet they had also been told that they were fraternal and stuck to that. But they were very similar behaviorally and physically, and very close to one another. I lost touch with them for many years, but we found each other again through various contacts. I mention their wonderful episode in my recent book, Indivisible by Two: Lives of Extraordinary Twins. They noticed some unusual similarities in their children (who would be equivalent to half-siblings if the twins were identical; I will write more about that in a later blog) and began to wonder if they might not be identical. I arranged to have their DNA tested, and my high school suspicions were confirmed. Upon learning that she was identical, Barbara wrote, “It’s a nice profound feeling.” Research shows that identical twins are socially close than fraternal twins, on average. It may be their similarities in intelligence, personality and temperament and/or their perceptions of their similarities that drive their relationships. In both these cases the twins believed for a good part of their lives that they were fraternal—yet they acted otherwise. I want to describe another revealing pair that I recently studied as part of an ongoing project in my laboratory at Cal State Fullerton—a study of behavioral similarities, differences and adjustment in young Chinese twins adopted apart, young Chinese twins adopted together, and young virtual twins (same-age unrelated siblings reared together). One parent was certain that her twins were fraternal, yet my scoring scheme did not yield a definitive answer. Inspecting the girl’s pictures suggested that they were identical, but the poses were slightly different and one girl was wearing glasses. I suggested having their DNA tested and the family agreed. Several weeks later the results came back, showing that the twins were, in fact, identical. This bit of information was surprising to their mother, but it made sense to me in light of the data I had gathered on them. I tell parents that they are not good judges of twin type because they are sensitive to subtle differences between the twins. I, on the other hand, meeting twins for the first time or looking at their photographs, am usually a better judge. It is strange, but true, that someone who does not know the twins can know so much about them. I am also asked why it may be important to know one’s twin type—because I believe that it is. In the event that one twin develops an illness or disorder it would be important to know the chance that the other twin might show the same symptoms. Being identical or fraternal might mean a lot in such cases—although while identical twins show greater match than fraternal twins on most measures, they do not show perfect similarity. In fact, recent work has shown that even identical twins can show DNA differences, in what are called copy number variations (when a genes exists in more than one copy). Studying such twins promises to tell us a great deal about the roots of normal and abnormal behaviors. In closing, I will mention one more curious case that bears on the issue of twin type. My study of Chinese twins reared apart requires DNA testing to confirm that the children are identical or fraternal twins. Note that many of these twins are reunited because they look alike. However, a problem for the non-identical twins is that without biological parent information, it is not possible to know for sure that the two children are related; it is only possible to assign a full-sib or half-sib index. I had the pleasure of working with the families of two little girls who bore a striking resemblance to one another—yet the laboratory indicated that they were not related at all. Disappointment and regret followed, testimony to the special qualities of being or having twins.

Why Identical Twins Fascinate Us – and the Case for Fraternals

Nancy L. Segal — Sat, 08 Mar 2008 14:20:07 -0800

Identical twins are intriguing, but most people cannot tell you why this is so. I have thought a great deal about this over the years that I have studied twins in my lab, interviewed them in their home or met them on the street. I think I may have one answer: We live in a world that appreciates and expects individual differences in appearance and in behavior. So when we encounter two highly matched individuals, this experience challenges our beliefs about the way that the world works. The likenesses of identical twins trigger a variety of reactions, both positive and negative, yet everyone is drawn in. Some people may even feel jealous of the social closeness most identical twins experience and celebrate. Of course, identical twins are never exactly alike, and some differ in profound ways, such as in disease susceptibility or in gender identity. These cases are truly extraordinary. I also want to make a case for fraternals who are often overlooked by the media, yet are warmly welcomed in scientific laboratories. There are many variations among fraternal twins—some have different fathers, some are conceived weeks apart and some look like they come from different ethnicities. We can learn a great deal about human behavior and development by taking a closer look at these multiples. Many topics can be explored in the singular world of twins. And they are not just interesting or entertaining (they are!), but they also offer a take on who we are and how we got there. I look forward to sharing my thoughts and experiences with twins, now and in the future.