Fraternal Twins: The Hidden Pairs

I was on the Today Show today, May 7, 2008. The taped session 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 (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, 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.