Abstract
On many levels and to many people stories about twins are interesting. Most interesting of these are surely the life stories of extraordinary twins. Nancy Segal brings both sides of her researcher-character to bear in her book: Indivisible by two: Lives of Extraordinary Twins. Segal has spent not only a career researching twins, but is also a twin herself; she takes a participant-observer position and recounts some memorable anecdotes and stories of numerous twins both to highlight some strange coincidences, and also to highlight a number of issues for researchers and politicians to consider.
An easy read as a whole, Segal's book tells some of the more unusual stories about twins, and highlighting those in which, regardless of separation by miles or years or even religious/political ideology, twins share more than they do not. For instance, a set of twins who were separated at birth went on to become not only firemen but also had a penchant for Budweiser and for putting their pinky finger under their beer can while drinking. Or a set of twins who were reared apart who both like science, astronomy, cherries, comic books, board games, and neither of whom were particularly motivated at 16, as most 16 year olds are, to get their licenses to drive. Or the oft-repeated tale of a set of twins reared apart, one in Nazi Germany, one in Jamaica, who both turned out to be very competitive, had the habit of sneezing loudly in elevators, and had controlling personalities. Without saying so, Segal leads the reader to a pressing question involving twins and evolutionary and non-evolutionary research: how many coincidences are needed before you believe the powerful influences of genes and biology on personality and life outcomes?
Two of the twins remarked upon above are worth further comment: The brothers reared apart in Germany and Jamaica. Both brothers were born as Jews but were separated due to family circumstances and were reared apart. The brother in Germany became not only a Catholic but was also a member of the Hitler youth, while the brother in Jamaica was raised a Jew and fought for the allies. As older adults, the brothers had much trouble reconciling their apparent political and religious differences. While they were always uncomfortable with expressing their feelings for each other, mutual letters revealed their emotions. But more importantly for the reader than such a tragic story is that these brothers' story is illustrative on how to deal with cultural, political, and religious confrontations that the world finds itself in today. Without giving it all away, it is about patience, listening, and perseverance.
Segal also addresses other topical issues, but again she does this so subtly that I am not even sure if it was intended. She interlaces various stories of twins' research with a little of the science of behavioral genetics. By doing so, she hedges between the academic community and especially the readership of this journal, who has, as a rule, accepted that the nature-nurture debate is a false dichotomy, and the layperson who may still think that this politicized debate is real. She describes two twins reared apart who liked different types of music. But when the other was introduced to music he disliked, he developed an interest in it. Before this exposure, one might have concluded that difference among these twins is due to differences in their environment. It turns out, however, that it was an exposure issue: they really did have more similar preferences than were apparent. In this and other examples, it is made clear that to pick genes or environment is a fool's errand, but also that genes are more powerful than a culture of rugged individualists might want to admit.
Segal did not write this book as a soapbox for peace and love, or for advocating political positions like stem cell research or cloning (topics she does address in her last chapter). The savvy academic reader will notice that she makes several points with her numerous anecdotes that could be taken as research leads.
For example, much debate has been generated over whether homosexuality and heterosexuality have genetic roots. Segal recounts a story about twins who differ in sexual orientation. Although this topic is surely of interest to the politically minded reader, it is an issue that should also be a calling to researchers. The twins in question shared the same genes and the same environment, yet despite these identical pre-conditions, the sexual orientations of the brothers were not the same. Segal recounts a similar story about how two identical twin sisters did not have the same gender identities. While one twin was content in being a woman, the other twin felt more like a man than a woman. This latter twin went on to get a sex change operation. While, these, like the example to come, may be anomalies, it behooves researchers to find ways to account for such anomalies in their models. This of course is a problem in all of psychology, but is one that may plague evolutionary psychologists the most, since they need to account for within-twins differences as well as similarities. So while these twins shared much, these particular differences loom large and deserve attention.
Another interesting point that warrants being addressed by evolutionary psychologists is Segal's report about two twin couples who met at a twin's convention in Texas, became romantically involved, and eventually married. However, the individual twins were each attracted to a different individual within the twin dyads. Even though these individuals were genetically identical, they were clearly attracted to something other than physical appearance, since physical appearance is a shared characteristic. Although Segal offers some tentative explanations, this should be taken up empirically. Much evolutionary work is focused on the role of physical attractiveness as a major predictor for romantic interest. Yet this story seems to fly in the face of that rather large body of literature.
Segal's anecdotes are not all so positive. Whereas she illustrates the deep emotional and perhaps spiritual connection between twins, as in the case of one twin being the surrogate mother for her infertile twin's baby, she also highlights the difficulties experienced by this rare subset of people. In one case she recounts how two adopted Chinese twins were separated at birth in China, but the individuals who adopted them discovered, by a strange twist of fate, this unfortunate oversight, and raise the girls together as best they can. While this story, on its face, appears to have a happy ending in one regard, these families have a problem. These families, like a number of others, have family members who require the creation of relationship names that we simply do not have. How, for instance, do you address your twin's adoptive mother? Segal also recounts a number of stories of brothers, like the firemen, who after a brief period of time became distant (just like many non-twin brothers I suspect).
Segal recounts these and other stories with an emotional slant, which will surely draw lay-people to this book; at the same time, she remains scientific enough to keep the interest of the academic. In this unique blend of science and story, Segal is able to discuss her work, the lives of these extraordinary twins, and to address some of the more pressing issues in politics and science.