My reading is about half fiction and half non-fiction; among non-fiction books, there are a lot of pop-science books; among the pop-science books, there are a lot of pop-psychology books. Some of the pop-psychology books have made interesting (but rather isolated) statements about twin studies. These statements intrigued me; surely the scientific study of twins deserved to be described in more depth. Finally, I’ve read a whole book about twin studies!
Author Nancy L. Segal is a researcher (and a twin) with an early 2000s-style website and a number of books to her name; this book, Entwined Lives: Twins and What They Tell Us About Human Behavior, isn’t the most recent book she’s published, but seems to be the most general. It may actually be the most accessible, general book on twin studies in existence. So if the topic interests you, read on.
Entwined Lives: Twins and What They Tell Us About Human Behavior
Before reading this book, I knew about the two major types of twins, fraternal and identical, but I didn’t realize there’s more to it than that! For one thing, in the absence of a blood test, families with same-sex twins often don’t really know whether they are identical or fraternal. Fraternal twins can resemble each other closely, and parents can perceive small differences between identical twins as larger than they are. In addition, before birth, twins might or might not share a placenta and/or amniotic sac, which can influence development in important ways, confounding simple notions of twin type.
(Incidentally, another thread of my reading (Innate, by neuroscientist Kevin Mitchell, Nature via Nurture by science writer Matt Ridley) reinforces the idea that individuality results not just from nature and nurture, but also from the genetically driven but partly random processes that build human bodies and, especially, brains. Sometimes this is called epigenetics.)
Segal of course talks about the various types of “natural experiments” that arise in families that adopted separated twins, especially if there are other children in the family, especially if the other children are of similar age. Identical twins (who have the same genes) but were raised in different environments give scientists a way to tease apart genetic and environmental factors relating to personality traits, mental disorders, and behavior in general. But again, the real picture is more complicated than the picture we’re given in brief mentions in pop-psychology books that only mention twins in passing. Segal has helped conduct twin studies at The Minnesota Center for Twin and Family Research, and can describe the design and results of such studies in proper scientific detail.
Segal’s book includes chapters devoted to the specialness of twinship (especially identical twinship), the correspondingly exquisite heartbreak of twin loss, fertility treatments that result in twins, twin athletes, animal twins, famous twins, legal cases involving twins, and conjoined twins.
If the book has a flaw, it’s that it has an academic tone despite being aimed at a more general audience. On the other hand, if this is the only book that even tries to convey the science of twin studies outside academia, then by definition it’s the best, and I’m glad it exists! If I could find another book about the science of twins (not a how-to-parent-your-twins book, of which there seem to be many, or a how-to-do-twin-research textbook, of which there is at least one), I would totally read it, but my searches on Amazon and Google haven’t turned up anything promising.
I did find a book called Twins: And What They Tell Us About Who We Are, but it’s also from 1999. I found another one, called
Fiction-wise, I found a novel titled Twin Studies. There’s also a Ken Follett novel (The Third Twin). Reminds me of the TV series Orphan Black, which is about an international alliance of clones (all played by the same actress). These depictions are proof that twins are inherently fascinating, whether or not they help us understand humanity in general.
When and Why I Read Entwined Lives
FINALLY I'm reading a book that I hope will shed more light on my understanding of the nature/nurture debate from the perspective of twin studies. Once in a while I read a sentence that suggests a surprising amount of similarity between identical twins is innate (twin brothers separated at birth both walk backwards into the sea?), but of course the reality is complex. And maybe after this I can read a book that's more recent than 1999, lol.
Genre: biology
Date started / date finished: 28-Dec-24 to 04-Feb-25
Length: 337 pages
ISBN: 0525944656
Originally published in: 1999
Amazon link: Entwined Lives
